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Oxidative Dissolution of Metals in Organic Solvents

Xiaohua Li
Xiaohua Li
KU Leuven, Department of Chemistry, Celestijnenlaan 200F, P.O. Box 2404, B-3001 Leuven, Belgium
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http://orcid.org/0000-0003-4555-8705
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Koen Binnemans*
Koen Binnemans
KU Leuven, Department of Chemistry, Celestijnenlaan 200F, P.O. Box 2404, B-3001 Leuven, Belgium
*Phone: +3216327446. Email: [email protected]
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Cite this: Chem. Rev. 2021, 121, 8, 4506–4530

Publication Date (Web):March 16, 2021

https://doi.org/10.1021/acs.chemrev.0c00917

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Abstract

Dissolution of metals in organic solvents is relevant to various application fields, such as metal extraction from ores or secondary resources, surface etching or polishing of metals, direct synthesis of organometallic compounds, and separation of metals from other compounds. Organic solvents for dissolution of metals can offer a solution when aqueous systems fail, such as separation of metals from metal oxides, because both the metal and metal oxide could codissolve in aqueous acidic solutions. This review critically discusses organic media (conventional molecular organic solvents, ionic liquids, deep-eutectic solvents and supercritical carbon dioxide) for oxidative dissolution of metals in different application areas. The reaction mechanisms of dissolution processes are discussed for various lixiviant systems which generally consist of oxidizing agents, chelating agents, and solvents. Different oxidizing agents for dissolution of metals are reviewed such as halogens, halogenated organics, donor–acceptor electron-transfer systems, polyhalide ionic liquids, and others. Both chemical and electrochemical processes are included. The review can guide researchers to develop more efficient, economic, and environmentally friendly processes for dissolution of metals in their elemental state.

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1. Introduction

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In contrast to many metals salts, metals in their elemental state cannot be dissolved in conventional solvents. Their dissolution must necessarily involve simultaneously an oxidation step, so that the dissolution of metals can be described as oxidative dissolution. In case only part of the solid is dissolved, oxidative dissolution of metals can be described as a leaching process. The solution used for leaching is called a leaching system, leaching agent, or lixiviant. For oxidative dissolution of metals, the lixiviant must contain at least one oxidizing agent (to oxidize the metal), often a solvent (water or a nonaqueous solvent) to dissolve the oxidizing agent, and sometimes a complexing agent to adjust the redox potential of the metals and/or the solubility of the produced metal compounds. Oxidative dissolution of metallic elements happens in various applications such as extraction of gold from gold-bearing ores, separation of metals from other compounds, chemical etching in the microelectronics industry, surface polishing of metals or alloys, and direct synthesis of organometallic compounds from metals. (1−4) Moreover, oxidative dissolution of metals could be relevant for recycling of valuable metals from secondary resources such as preconsumer production scrap and end-of-life products. (5,6) Many metals and alloys are essential for the production of components in high-tech devices, such as neodymium–iron–boron (NdFeB) permanent magnets used in electric motors and wind turbines and platinum-group metals (PGMs) used in car exhaust catalysts. Rare-earth elements (REEs), together with PGMs, are on the lists of critical raw materials of the European Commission and the United States of America, because of their high economic importance and high supply risk. (7,8) Recycling of metals is essential in a circular economy.

Conventional methods for dissolution of metals are water-based and the metals are oxidized in aqueous solutions by, for example, strong mineral acids such as hydrochloric acid and sulfuric acid with evolution of hydrogen gas. However, these nonoxidizing mineral acids are not able to dissolve noble metals such as gold, silver, and platinum. Current technologies for dissolution of noble metals involve the use of aqua regia or sodium cyanide (in the presence of oxygen gas), which cause serious safety and environmental concerns. (9,10) Their use will probably be restricted in the near future. Therefore, the development of new efficient, economic, and environmentally benign leaching systems for metal dissolutions is a very relevant research activity.

Dissolution of metals by oxidizing agents in organic solvents is an alternative approach. The organic solvents can be conventional molecular organic solvents, ionic liquids (ILs), deep-eutectic solvents (DESs), or supercritical carbon dioxide (scCO₂). Metal processing in organic solvents or mixed with small amounts of water (<50 vol %) is termed “solvometallurgy”, which is an emerging branch of extractive metallurgy and complementary to hydrometallurgy and pyrometallurgy. (11) Examples of solvometallurgy are solvo-leaching, nonaqueous solvent extraction, nonaqueous precipitation and electrodeposition. (12−16) When ionic solvents such as ionic liquids (ILs) or deep-eutectic solvents (DESs) are involved, the term “ionometallurgy” could be used. (17) Dissolution of metals in organic solvents offer several advantages compared to aqueous solvents. Organic solvent systems usually generate smaller volumes of aqueous waste streams and are often more selective than aqueous systems. One of the earliest studies on the dissolution of metals in organic solvents dates from more than 70 years ago and is about the dissolution of uranium using elemental halogens as oxidizing agents. (18) The number of papers published on the topic of oxidative dissolutions of metals in organic solvents grew very slowly in the beginning, but increased rapidly after the year 2000 (Figure 1), due to the search for new, efficient, and environmentally friendly processes for the extraction of metals from metal ores and secondary resources. At present, the total number of publications on oxidative dissolution of metals in their elemental state in organic solvents is still less than 200.

Figure 1. Number of publications on dissolution of metals in organic solvents.

This review describes the different strategies for the oxidative dissolution of metals in organic solvents and possible applications of this approach. The review covers the literature from the 1950s until December 2020. Only research of oxidative dissolution of metals in their metallic state (oxidation state zero) is presented in this review, so that research on dissolution of other metal compounds such as metal oxides and sulfides has been omitted. Special attention has been paid to ionic liquids and deep-eutectic solvents, because their use for oxidative dissolution of metals is emerging. The various oxidizing systems show different mechanisms for the oxidative dissolution. To better understand the reaction mechanism in the different reaction media, this review is organized according to the different types of oxidizing agents. ILs and DESs are all combined in one section, irrespective of whether they have been used as oxidizing agent or as solvents, in order to highlight their application in oxidative dissolution of metals. The different types of organic leaching systems, together with the studied oxidative dissolution of metals in the corresponding systems, are summarized in Figure 2. The aim of this review is to give an overview of the emerging research field of oxidative dissolution of metals in organic solvents. By highlighting the oxidation reaction mechanisms, this review can be helpful for the development of new efficient, environmentally benign, and economic processes for dissolution of metals in their elemental state for various applications.

Figure 2. Overview of the organic leaching systems and the metals that have been studied for oxidative dissolution in the corresponding leaching systems.

2. Solutions of Halogens in Polar Organic Solvents

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Many studies on the oxidizing dissolution of metals in organic solvents use halogens, because they are strong oxidizing agents. Various metals can be dissolved directly in solutions of halogens in polar organic solvents, such as bromine in ethyl acetate (EtOAc) or methanol (MeOH) or chlorine in N,N-dimethylformamide (DMF). Addition of suitable ligands can enhance the dissolution of noble metals such as gold and platinum. These ligands can be simply halide compounds (e.g., tetraethylammonium iodide) or organic compounds such as dithio-oxamide. The subsections in section 2 are defined on the basis of the types of ligands in the leaching system. Subsection 2.1 describes halogen leaching systems without added ligands, and subsection 2.2 covers halogen leaching systems with halide anions as ligands, whereas subsection 2.3 is about organic compounds that can form adducts with halogens.

2.1. Halogens in Organic Solvents

The simplest organic lixiviants for the dissolution of elemental metals are solutions of halogens in an organic solvent. The halogens act as oxidizing agents to oxidize the metal from oxidation state zero to a higher oxidation state, which can be dissolved in the organic solvent. Examples of commonly used organic solvents are ethanol (EtOH), methyl acetate (MeOAc), butyl acetate (BuOAc), ethylene glycol (EG), acetonitrile (ACN), and tri-n-butylphosphate (TBP). A major application of organic solvent–halogen mixtures is the quantitative analysis of nonmetallic phase impurities in metals and alloys, because the metals in their elemental state are oxidatively dissolved, but metallic compounds (e.g., oxides and borides) and nonmetallic components (e.g., boron) are not soluble. (19−23) Other applications are the dissolution of metals or metal alloys, the chlorination of metals, and the chemical etching and polishing of semiconductors. (3,24−30) Leaching systems containing halogens and organic solvents used for dissolution of metals in various application fields are summarized in Table 1. Due to the large variety of combinations of halogens with organic solvents, this subsection is further divided into three subsections based on the type of halogens.

Table 1. Leaching Systems Using Halogens as Oxidizing Agents in Organic Solvents for Dissolution of Metals in Various Application Fields

Solvent system	Metals studied	Application	References
Br₂-EtOAc	U, Nd, Sm, Ce, Pr, La, Y, Ga, Zr	Separation of metals and metal oxides	(2,18,31)
Br₂-MeOH	Be, Zr, Th, U	Phase analysis (B content in metals)	(19)
	GaAs, GaP	Polishing or etching of semiconductors	(3,24,25)
	Fe	Determination of iron content in rusted iron sponge	(32)
	Ni	Phase analysis (TiC-Ni cermets)	(33)
X₂ (Cl₂, Br₂, I₂, ICl, Cl₃^–) -organic solvents (MeOH, MeOAc, BuOAc, ACN)	Al, Cr, Co, Cu, Fe, Pb, Mn, FeMo, Ni, FeNi, P, FeSi, S, Sn, Ti, FeW, V,	Phase analysis	(20−23)
Cl₂-DMF	Mo	Chlorination	(26)
Cl₂-DMF-H₂O	Re, W, Mo	Chlorination	(27)
Cl₂-DMF-HCl	Re, Pt	Chlorination	(28)
Cl₂-DMF-FeCl₃	Zr	Chlorination	(29)
Cl₂-tetrachloroethylene (TCE)-TBP	U	Chlorination	(30)
Br₂-organic solvent (EtOH, DMF, EG, EtOAc, MeOAc)	Ni, Cu	Remove coatings from SmCo magnets	(34)
Br₂-EtOH	Au, Ag, Pt	extracting noble metals from solid residues after mineral acid leaching of raw materials	(35)

2.1.1. Bromine in Organic Solvents

Bromine is the most used halogen in organic solvents for oxidative dissolution of elemental metals, because of its moderate oxidizing power, which allows bromine to oxidize metals but not aggressively react with organic solvents. Various organic solvents (e.g., EtOAc, MeOAc, ACN, MeOH, EtOH) mixed with bromine have been studied for dissolution of metals in various applications. The reaction of bromine with metals can be described in eq 1:

(1)

where M represents a metallic element and x is the oxidation state of the metal. Solutions of bromine in ethyl acetate (Br₂-EtOAc) have been investigated mostly for dissolution of uranium metal for nuclear applications. Elemental uranium is very reactive and can be dissolved rapidly in common mineral acids, such as nitric acid or hydrochloric acid. However, for the dissolution of uranium alloys with refractory alloying metals such as zirconium, aggressive reagents such as hydrofluoric acid, with or without extra added fluoride salts, have to be used to ensure complete dissolution of the uranium–zirconium alloy. (18) Dissolution of such alloys in organic solvents is useful when fluoride ions must be absent for the subsequent analysis or for avoiding aggressive reagents. Bromine in ethyl acetate (Br₂-EtOAc) reacts rapidly with both uranium and zirconium metal to form UBr₄ and ZrBr₄. (18) Organic solvents other than ethyl acetate have been tested as solvents for bromine to dissolve uranium metal, but these solvents did not perform as well as ethyl acetate. (18) Br₂-EtOAc was successfully used for separation of metals from their oxides, including metallic uranium, magnesium, aluminum, and zinc. By using a solution of Br₂-EtOAc to selectively separate uranium and rare-earth metals from their oxides, the yield of electrochemical reduction of the simulated oxide spent nuclear fuel in the molten salt mixture LiCl-Li₂O was estimated. (31) However, Br₂-EtOAc is not reactive enough for dissolution of noble metals and their alloys.

Solutions of bromine in alcohols are one of the most studied leaching systems in the category of bromine in organic solvents. Bromine in EtOH can be used for extracting noble metals such as gold, silver, and platinum from raw materials. (35) The raw materials containing noble metals were first leached in a mineral acid at temperatures 95–100 °C to leave the noble metals in a solid residue that was then treated with bromine in organic solvents twice. The recovery efficiency of noble metals could reach >95%. Recently, bromine in organic solvents has shown potential for removal of the metallic nickel–copper–nickel protective coatings of rare-earth permanent magnets (Nd–Fe–B and Sm–Co magnets), prior to recycling of the rare-earth elements. (34) Among five solvents tested, namely 1 vol % of bromine in EtOH, DMF, EG, EtOAc, and MeOAc, the first two solutions could selectively dissolve nickel and copper without leaching the magnet alloy (Figure 3). Dissolution of metals in Br₂-EG was slow due to the high viscosity of EG which is 1 order of magnitude higher than that of ethanol or DMF. The slow dissolution rate of metals in the MeOAc and EtOAc mixtures was attributed to the low solubility of the formed metal salts in these solvents. This solvometallurgical process performed better than an aqueous 2 M HNO₃ solution, which could dissolve nickel but not copper.

Figure 3. Screening dissolution test for the SmCo₅ (top) and Sm₂Co₁₇ (bottom) permanent magnets at 20 min in 1 vol % Br₂ in EG, DMF, EtOH, MeOAc, and EtOAc. The recovery yields, η (%), were the ratio of the concentration of a metal in solution after leaching for 20 min to the concentration of the same metal if all the content of the coating would be dissolved in solution. Reprinted from ref (34). Copyright 2019 Royal Society of Chemistry under [CC BY-NC 3.0] [https://creativecommons.org/licenses/by-nc/3.0/].

Bromine in methanol (Br₂-MeOH) is another example of a bromine-alcohol mixture. It has been tested for the determination of boron in metals such as beryllium, zirconium, thorium, and uranium, by selective dissolution of the metal, followed by distillation of the formed boron methyl ester. (19) With the anhydrous reaction mixture, traces of boron could be completely recovered by distillation. Another application of Br₂-MeOH is for phase analysis, to quantify the composition of the titanium carbide-nickel cermets, more specifically to determine the amount of titanium present in a metallic nickel binder. Br₂-MeOH was used as solvent at a low temperature (−20 °C) to dissolve the metallic phase without affecting the titanium carbide. (33) Br₂-MeOH has also been used for processing of semiconductors, for instance for chemical polishing of gallium arsenide and for etching of gallium phosphide. (3,24,25) The etching behaviors of GaP in Br₂-MeOH and in aqueous solutions of Br₂ were similar, so that it seems preferable to use the aqueous solution for etching, considering the toxicity of Br₂-MeOH. However, the advantages of Br₂-MeOH solutions must be taken into account as well. For example, the reproducibility of the measurements in Br₂-MeOH solutions was higher than that in the aqueous Br₂ solutions. Moreover, Br₂ has a higher solubility in methanol than in water. The metallic iron content in a rusted iron sponge was determined by using a solution of Br₂-MeOH to selectively dissolve iron metal, leaving behind the iron oxides. (32)

Although Br₂-MeOH can oxidatively dissolve metals, this system must be used with much caution. First, it must be stressed that it can be dangerous to prepare solutions of bromine in alcohol solvents, especially when the concentration of bromine is above 10 vol %. It was reported that by mixing a 50 vol % Br₂-MeOH solution in a 250 mL volumetric flask, within seconds the solution was violently expelled from the flask. (36) This is due to a strongly exothermic reaction between bromine and alcohol. Moreover, the vigorous reaction of bromine with methanol may generate gaseous products which could also eject the solution from the flask. Therefore, leaching of the metal with Br₂-MeOH should be performed at room temperature, to avoid the rapid reaction between Br₂ and MeOH at elevated temperatures. Second, the reaction of Br₂ with MeOH could produce HBr and water. These products dissolve oxides so that the selectivity of metal dissolution decreases when metal oxides are present. Therefore, magnesium oxide is sometimes used to neutralize the formed acids to prevent the dissolution of oxides. Third, the reaction should be performed under anhydrous conditions, since water can react with Br₂ forming HBr as well. For example, the use of a nonaqueous solution is mandatory in the application of quantification of titanium in titanium carbide-nickel cermets, because the HBr formed by hydrolysis of bromine can react with the carbide, resulting in errors in the phase analysis. (33)

2.1.2. Chlorine in Organic Solvents

Chlorination of refractive metals such as molybdenum, tungsten, uranium, zirconium, rhenium, and platinum has been studied by using chlorine in organic solvents, among which chlorine in DMF was the often used leaching system. (26−29) It is known that halogens can react with organic solvents, (18,36) but the influence of these side reactions on the dissolution of metals has been studied only occasionally. Drobot et al. studied the oxidative dissolution of molybdenum by chlorine gas dissolved in DMF. (26) The IR and EPR spectra of the solutions obtained after chlorination of molybdenum suggested that the formed complexes are the diamagnetic Mo(VI) and paramagnetic Mo(V) complexes of composition R₂[MoOCl₅], where R is [(CH₃)₂NCOH₂]⁺ and [(CH₃)₂NH₂]⁺. Moreover, the complex [(CH₃)₂NH₂][MoOCl₅] is not stable upon prolonged storage and decomposes to form [(CH₃)₂NH₂]Cl, indicating that the DMF solvent participates in the chlorination reaction. Therefore, DMF not only acts as solvent for chlorine but also enhances the chlorination reaction due to the formation and destruction of the formed molybdenum complex. The mechanism of chlorination of molybdenum could be described by the reactions given in Scheme 1. (26)

Scheme 1. Chlorination of Molybdenum by Chlorine in DMF

Addition of water can enhance the oxidative dissolution of metals in chlorine-DMF. (27) For example, when chlorine in DMF was used as a leaching system, only small amounts of rhenium and tungsten (<5%) could be oxidatively dissolved. However, an increase in the water content in the leaching system resulted in a higher amount of metals dissolved in the solution. Further increase in the water content resulted in a decrease of the dissolution of molybdenum and tungsten (Figure 4). Quantitative dissolution of rhenium was attained by adding 30 to 40% water with respect to the volume of DMF.

Figure 4. Effect of water on dissolution of metals in solutions of chlorine in DMF. (Data were extracted from ref (27).)

Chlorination of refractory metals in DMF–H₂O mixtures is much more efficient than that in the neat organic solvent. This is due to the fact that mixing of water and DMF can rupture some hydrogen bonds between water molecules and form new hydrogen bonds between the carbonyl oxygen atoms of DMF and water molecules. This new arrangement facilitates the molecular interaction between DMF and other molecules in the system. On the other hand, in the presence of chlorine gas, addition of water induces the formation of HCl and HClO. The new complex [(CH₃)₂N–CH═OH]⁺Cl^– is formed with a hydrogen bond between the carbonyl oxygen atom of DMF and HCl (see Scheme 2). This protonated DMF molecule can further react with the chlorine-containing anion, e.g. [MOCl₅]^2–, to form an adduct, and this enhances the dissolution of metals.

Scheme 2. Complex Formed between DMF and HCl

Similarly, addition of HCl in Cl₂-DMF can enhance the oxidative dissolution of metals as well. Chlorine in DMF with addition of water or HCl solutions was applied to recover rhenium and platinum from end-of-life platinum–rhenium catalyst on an aluminum support. (28) The influence of HCl on the dissolution efficiency was similar to that of water. One leaching step at 25–60 °C could dissolve 80 to 90% of rhenium, while less than 50% of platinum was dissolved, due to the modified (coked) state of platinum in the spent catalyst. After a decarbonization process (to burn off carbon at about 500 °C), a second chlorination leaching step was conducted, resulting in 70–94% of platinum recovery and 91–96% of rhenium recovery. (28) No heating was required for the leaching step, and this is a cheap leaching system.

The presence of the Lewis acid FeCl₃ in Cl₂-DMF can influence the kinetics of dissolution of zirconium as well. (29) The dissolution rate of zirconium metal increased appreciably relative to the FeCl₃-free system. A maximum in the dissolution rate was observed at 1.5 g/L of FeCl₃, and further increase of the FeCl₃ content resulted in a rapid decrease of the dissolution rate. The dissolution of zirconium and the catalytic effect of FeCl₃ could be described by eqs 2–5:

(2)

(3)

(4)

(5)

Besides DMF, tetrachloroethylene (TCE) was used as solvent, in combination with TBP (complexing agent) and chlorine as oxidizing agent for low-temperature chlorination of uranium metal. (30) Uranium reacted with chlorine to form UCl₄, which further complexed with TBP to form UCl₄·2TBP (eq 6):

(6)

The dissolution rate increased with increasing concentrations of chlorine and TBP. Similar to the DMF-Cl₂ leaching system, addition of water (0.2–0.6 vol%) did increase the dissolution rate significantly. The dissolution rate decreased with a further increase in water content. A maximum in dissolution rate was observed for a water content of 0.2–0.6 vol%. The function of TCE was not specifically mentioned in the paper, but it can be supposed to act as a diluent. The reason for the positive effect of water addition is probably the formation of HCl that can complex with TBP and enhance the metal dissolution. (11)

Chlorine can be used as a strong oxidizing agent for metals, but the fact that it can react with organic solvents as well makes the recycling of the organic solvent difficult. In some cases the strong reactivity of chlorine toward organic solvents with formation of chlorinated organic compounds has a negative effect on the dissolution of metals. For example, bromine in EtOAc was preferred over chlorine in EtOAc for dissolution of uranium metal. (18)

2.1.3. Other Halogens in Organic Solvents

One of the main applications of solutions of halogens in organic solvents is phase analysis of metals or alloys, to determine the concentration of impurities such as metallic compounds (e.g., oxides, sulfides) and nonmetallic compounds (e.g., boron, carbon) in metal alloys by selectively dissolution of metals. Pioneering work was performed by Beeghly, who used bromine-methyl acetate (Br₂-MeOAc) solvent for the quantitative isolation of aluminum nitride from steel alloys. (20) All nitrogen was recovered as insoluble aluminum nitride after dissolution of steel samples in the lixiviant. Inspired by this work, Headridge and co-workers investigated the feasibility of quantitative separation of carbide, nitride, oxide, and sulfide inclusions from metals by using solutions of halogens in organic solvents. (21−23) For useful phase analysis, it is necessary that only the metals in their elemental state oxidatively dissolve in the leaching system, and other compounds such as oxides and nitrides that are present in metal alloys do not. Therefore, the reactivity of various metals in the elemental state and of metal compounds (oxides, nitrides, sulfides, carbides) with bromine in organic solvents MeOAc, BuOAc, and ACN was investigated. Additionally, the solubilities of the corresponding metal bromides formed by the reactions and of the metal compounds (oxides, nitrides, sulfides, carbides) in the leaching systems were reported. All the studied elements or alloys were found to react with bromine: aluminum, chromium, cobalt, copper, iron, lead, manganese, ferromolybdenum, nickel, ferroniobium, phosphorus, ferrosilicon, sulfur, tin, titanium, ferrotungsten, and vanadium. The study of the solubility showed that most of the metal bromides can dissolve in the organic solvent–bromine mixtures, but some metal bromides were poorly soluble, such as the bromides of lead, molybdenum, silicon, and tungsten. (21) The poor solubility of metal bromides could limit the oxidative dissolution of these metals in the leaching systems. Most studied carbides, nitrides, and oxides of metals have low reactivity and solubility in Br₂-ACN and Br₂-MeOAc, whereas most sulfides have a significant solubility and some sulfides can react with the leaching agents violently. Therefore, organic solvent–bromine mixtures can be used for isolation of most carbides, nitrides, and oxides but not sulfides from metals. (23)

Subsequently, more organic solvent–halogen mixtures were used to study the solubilities of manganese silicon nitride, metals and their nitrides, carbides, oxides, and sulfides. The studied organic solvents were MeOH and MeOAc, and the halogens were Cl₂, Br₂, I₂, ICl, and ICl₃. (22) Based on the reactivity and solubility of the metals and metal compounds in the leaching systems, a method was proposed to determine in steel the contents of total nitrogen, of mobile nitrogen, of nitrogen as manganese silicon nitride, and of nitrogen as aluminum nitride. A mixture of I₂-MeOAc can be used in the first step to isolate manganese silicon nitride and aluminum nitrides while dissolving metals; subsequently, ICl₃-MeOAc can be used to isolate aluminum nitride, while dissolving manganese silicon nitride. (22) Therefore, organic solvent–halogen mixtures can be used to quantify nonmetallic phases in metals. Moreover, the organic solvent has a slight influence on the solubility of the metal bromide. For example, acetonitrile with its higher dielectric constant (ε = 36.5 at 25 °C) is a better coordinating solvent for ions and is thus a better solvent for divalent metal bromides than methyl acetate and butyl acetate with dielectric constants of ε = 6.7 (25 °C) and ε = 5.0 (20 °C), respectively. (21)

2.2. Halogens + Halide Ligands + Organic Solvents

The dissolution efficiency of metals largely depends on the solubility of the reaction products (metal halide salts) in the organic solvents. Increasing the solubility of the salts formed could suppress formation of a passivating layer and hence increase the dissolution efficiency. Moreover, addition of complexing agents to the organic solvent could change the redox potential of metals and hence the dissolution behavior of the metals. In the 1990s, Nakao and co-workers carried out a series of studies on the dissolution of metals with an organic lixiviant consisting of an elemental halogen, a halide salt, and a common organic solvent. (4,37−43) They used the halogens chlorine, bromine, and iodine. Most of the used halide salts were quaternary ammonium halide, but metal halides such as KI, KBr, and NaI were tested as well. A variety of organic solvents including hydrocarbons, organic halides, alcohols, ketones, esters, and nitro compounds was investigated. Bromine–cetylpyridinium bromide (CPB)–benzene and iodine–cetylpyridinium iodide (CPI)–benzene were found to be effective for the dissolution of various metals, such as Fe, Ni, Cu, Zn, Au, Ag, Pd, Cr, Mn, Co, Ga, Ge, Se, Cd, In, Sb, Hg, and Pb. (37) The metals were dissolved in the form of metal complex anions, such as [AgBr₂]⁻, [AuBr₄]⁻, [NiBr₄]^2–, [ZnBr₄]^2–, and [PdBr₄]^2–. In the dissolution process, the halogens acted as oxidizing agents and the halide compounds as complexing agents to allow the products to be soluble in the leaching systems. Besides tests on pure metal wires, gold and silver were efficiently extracted from quartzite ore (containing 13.1 ppm of gold and 389.2 ppm of silver) with the same lixiviant. (41) Organic solvents can react with halogens, but in the presence of CPB or CPI, the reactivity of halogens is largely reduced, due to the formation of tribromide or triiodide anions by reaction between the halogens and the halide salts. These trihalide anions are still active to metals, but less active toward the organic solvents than elemental bromine and iodine. However, in most cases, elemental chlorine could not be used, because the trichloride anion is quite reactive toward organic solvents. On the other hand, it was observed that acetonitrile is very resistant toward chlorine at low temperatures. Thus a mixture of chlorine with chloride salts in acetonitrile can be used for oxidative dissolution of metals. Several lixiviants in acetonitrile comprising chlorine and different organic halide salts such as tetraethylammonium chloride, trimethylamine hydrogen chloride (Me₃NHCl), and tetraethylammonium bromide were compared with lixiviants using inorganic halide salts such as I₂–NaI–acetone, Br₂–KBr–methanol, and I₂–KI–methanol for dissolution of noble metals. (38) All these systems could dissolve palladium, gold, and silver, except that silver could not be dissolved in the methanol systems, because of the formation of a passivating layer of silver halide on the silver metal surface. It was observed that chlorine reacted faster than bromine and iodine. Moreover, it was found that the system Cl₂–Me₃NHCl–acetonitrile did dissolve gold more rapidly than aqua regia at 30 °C.

An interesting phenomenon was observed in the I₂–I^– organic solvent system: when the molar ratio I₂/I^– was larger than 0.5, gold dissolved on heating as [AuI₂]⁻ and, upon cooling, part of the gold was deposited from the pregnant solution via formation of [AuI₄]⁻ and Au by a disproportionation reaction. When a new piece of gold was added to the resulting solution under reflux, an amount of gold equal to that deposited before was redissolved and upon cooling was redeposited. This process could be repeated several times. Such reversible dissolution/deposition behavior was not observed for any other metals, nor in Cl₂–Cl^–-organic solvent and Br₂–Br^–-organic solvent systems, in which gold dissolved exclusively in the form of very stable [AuX₄]⁻ complexes. (40) However, upon addition of methanol, the reversible dissolution/deposition processes can be induced in all systems of X₂-X^––organic solvent (X = Cl, Br, and I). (39)

Organometallic complexes can be synthesized in one step by dissolving the corresponding metals in the above-mentioned organic solutions. (4) This direct synthesis method can avoid the handling of hygroscopic metal halides as reagents. Lower valence metal compounds (for instance ferrous or cuprous compounds) can be obtained by selecting an appropriate molar ratio of X₂/metal.

2.3. Dihalogen or Interhalogen Adducts

Halogen adducts are formed by the interaction between a σ-donor with a relatively high-lying HOMO and a dihalogen as an acceptor with a relatively low-energy LUMO (σ*). It has been found that these dihalogen adducts are capable of oxidizing elemental metals, including noble metals. The reactions between metals and diiodine and dibromine adducts with phosphine, arsine, and antimony donors have been studied. (44−49) Examples of such adducts are diiodotrimethylarsine (Me₃AsI₂), diiodotriphenylantimony (Ph₃SbI₂), and dibromotrimethylphosphorus (Me₃PBr₂). These adducts can react with metals (e.g., Mn, Zn, Co, Ni, and Au) to form complexes with various structures. The nature of the formed metal complexes is strongly dependent on both the organic group and the halogen. Gold reacts with Me₃AsI₂ to form the square-planar complex [AuI₃(AsMe₃)], whereas the same metal reacts with Me₃PI₂ to form the trigonal-bipyramidal complex [AuI₃(PMe₃)₂]. (49) Besides new perspectives in the field of inorganic chemistry, these results open the door to new applications of dihalogen adducts for recovery of noble metals from secondary resources or for metal refining. Unfortunately, the adducts with phosphine and arsine donors are very toxic and they require strictly anhydrous, anaerobic conditions and long reaction times.

A series of new oxidation reagents of dihalogen adducts bearing S,S-donors or adducts on the basis of thioamide have been reported for dissolution of metals such as noble metals, cadmium, and mercury (Table 2 and Scheme 3). (50−61) These adducts were prepared by simply mixing dihalogen or interhalogen with the donors in organic solvents such as CHCl₃ or THF at room temperature. The resulting compounds have been claimed to be safe, inexpensive, easy to handle, and noncytotoxic. Proper choice of polyfunctional donors that favors the preferred geometry required by the metal undergoing oxidation is believed to enhance the oxidation reaction. Most of the synthesized adducts were applied for dissolution of noble metals such as gold, palladium, and platinum. The softness of the donor atoms, as well as the chelating properties of the two vicinal thiones stabilize the oxidized noble metals in the d⁸ configuration.

Table 2. Names and Abbreviations of Organic Ligands to Form Halogen Adducts

Name	Abbreviation
N,N’-dimethylperhydrodiazepine-2,3-dithione	Me₂dazdt
N,N’-dimethylpiperazinium-2,3-dithione	Me₂Pipdt
tetraethylthiuram disulfide	Et₄TDS
3-methyl-benzothiazole-2-thione	mbtt
1-methyl-1H-benzimidazole-2(3H)-thione	mbit
N,N’-diphenyl dithiomalonamide	(PhHN)₂DTM
dimorpholyldithiomalonamide	Mo₂DTM

Scheme 3. Structures and Abbreviations of the Reported Organic Ligands to Form Halogen Adducts

The most extensively studied compound is the bis-diiodine adduct of N,N’-dimethylperhydrodiazepine-2,3-dithione (Me₂dazdt·2I₂) which can oxidatively dissolve gold and palladium under mild conditions in organic solvents. (50,61) The oxidation reactions are shown in Scheme 4. The reaction product after dissolution of gold was identified as the square-planar [AuI₂(Me₂dazdt)]I₃, where gold(III) is coordinated with two iodide ligands and one S,S-chelating ligand Me₂dazdt. However, the reaction product after palladium dissolution was identified as [Pd(Me₂dazdt)₂](I₃)₂, wherein the first coordination sphere of palladium(II) comprises two bidentate Me₂dazdt ligands. The reagent Me₂dazdt·2I₂ was tested for practical applications, for example the recovery of gold from waste inkjet printer cartridges and SIM cards. (57) It was used for failure analysis on end-of-life microelectronic devices by selectively removing the upper layer of gold from the multilayer system such as Ti/Pt/Au in GaAs-based devices, without destroying the electrical contacts. (52) The reagent allowed for quantitative recovery of palladium from a spent car exhaust catalyst (0.5–3.0 wt % Pd supported on Al₂O₃ and CeO₂–ZrO₂/Al₂O₃). (61) The adduct Me₂dazdt·2I₂ cannot dissolve platinum or rhodium metal, either at room temperature or in refluxing THF or CH₃CN. Therefore, palladium can be selectively recovered when platinum or rhodium is also present in the spent car catalyst. Moreover, it was found to be much more efficient than the aqueous lixiviant I₂/I^–, which could recover only 11% of the palladium from the same sample of spent car exhaust catalyst under the same conditions. Metallic palladium could easily be obtained by heating the formed complex [Pd(Me₂dazdt)₂](I₃)₂ at 600 °C for a few minutes. However, the ligand is destroyed during the thermal treatment of the complex to recover metallic palladium. This lowers the economic, environmental, and elemental sustainability of the recovery process. Therefore, the obtained complexes [Pd(Me₂dazdt)₂](I₃)₂ and [PdI₂(Me₂dazdt)] have been valorized themselves rather than recovering palladium metal from them, for instance as catalysts in the regio- and chemoselective C–H functionalization of benzo[h]quinoline to 10-alkoxybenzo[h]quinoline and 8-methylquinoline to 8-(methoxymethyl)quinoline in the presence of the oxidant PhI(OAc)₂. (59) Palladium powder can also be oxidized by a diiodine tellurium adduct (2-PyTe)₂···I₂ at room temperature with formation of a square planar geometry complex [PdI(TePy-2)(I₂TePy-2)₂] (Scheme 5). (62)

Scheme 4. Oxidative Dissolution of Gold and Palladium with Me₂dazdt·2I₂ in Organic Solvent at Room Temperature

Scheme 5. Synthesis of a Palladium Complex from a Diiodine Tellurium Adduct

Various dihalogens or interhalogens can form adducts with dithio-oxamide donors such as IBr, ICl, Br₂, or I₂. (54) The oxidation power of the adducts can be tuned by varying the halogens. The adducts of Me₂dazdt·2IBr have been tested for dissolution of gold. The square-planar complex [Au(Me₂dazdt)Br₂]IBr₂, with a structure similar to that of the complex [AuI₂(Me₂dazdt)]I₃, was formed by reaction between gold and Me₂dazdt·2I₂. The ligands act as an S,S-chelating ligand, and two halide ligands complete the first coordination sphere of gold(III). The effectiveness of these adducts in THF solutions for gold dissolution was compared with conventional I₂/KI aqueous lixiviants, and the following trend was found: Me₂dazdt·2I₂ > Me₂dazdt·2IBr > I₂/KI. Besides a faster dissolution rate, the adducts also showed better etching behavior than I₂/KI solutions. It was observed that gold etching by adducts was uniform, while the I₂/KI-etched gold surface appeared porous and its color changed to red. This color was attributed to gold nanoparticles. A comparison of the cyclic voltammograms of the Me₂dazdt·2IBr and Me₂dazdt·I₂ adducts with that of IBr and I₂ in anhydrous CH₂Cl₂ suggests that the halogens are the only electroactive species in the oxidative dissolution process.

The adduct N,N’-dimethylpiperazinium-2,3-dithione triiodide, [Me₂Pipdt]I₃, is of interest because it can act as a powerful oxidation agent toward metallic platinum, with formation of the square-planar complex [Pt(Me₂pipdt)₂](I₃)₂ (Scheme 6). (51) In contrast to the neutral adduct Me₂dazdt·2I₂, the adduct [Me₂Pipdt]I₃ is a salt, in which the cation is formed by the protonated ligand and the anion is a triiodide. Similarly to Me₂dazdt·2I₂, the adduct [Me₂Pipdt]I₃ can also react with other metals such as copper, silver, gold, and platinum. However, only [Me₂Pipdt]I₃ reacts with platinum, whereas Me₂dazdt·2I₂ does not. This difference in reactivity is most likely due to differences in the geometry of the ligand: Me₂dazdt has a seven-ring structure, while Me₂Pipdt has a six-ring structure. The six-ring structure probably favors the required geometry of the formed platinum complex. The adduct [Me₂Pipdt]I₃ can also quantitatively dissolve the hazardous elements cadmium and mercury in a one-step reaction. (53) The formed complex [CdI(Me₂pipdt)₂]I₃ has a coordination geometry intermediate between square-pyramidal and trigonal-bipyramidal, while the complex [HgI₂(Me₂pipdt)] shows a distorted tetrahedral geometry (Figure 5).

Figure 5. Molecular structure of (a) [CdI(Me₂pipdt)₂]I₃ and (b) [HgI₂(Me₂pipdt)], with thermal ellipsoids depicted at the 30% probability level. Symmetry code = −x; y; ¹/₂ – z. Reprinted with permission from ref (53). Copyright 2014 Elsevier B.V.

Scheme 6. Oxidative Dissolution Reaction of Platinum by [Me₂Pipdt]I₃ in Acetonitrile (Reflux for 4 days)

The donors of dihalogen adducts have been extended to other types, such as tetraethylthiuram disulfide (Et₄TDS), 3-methyl-benzothiazole-2-thione (mbtt), and 1-methyl-1H-benzimidazole-2(3H)-thione (mbit). (56,58) Their structures are shown in Scheme 3. The mixture of Et₄TDS and I₂ in acetone solutions can dissolve metallic gold powders and can etch a thin layer of gold from photonic devices with Si/SiO₂/Ti/Au multilayer structures. By changing the molar ratio of Et₄TDS to I₂, a variety of gold complexes can be formed, such as [Au(Et₂dtc)₂][AuI₂], [Au(Et₂dtc)I₂], [Au(Et₂dtc)₂]I, and [Au(Et₂dtc)₂]I₃ (Et₂dtc = N,N-diethyldithiocarbamate). The examples of formation of different complexes are shown in Scheme 7. The mixture of Et₄TDS and I₂ was also applied for gold recovery from real Waste Electrical and Electronic Equipment (WEEE) materials. (60)

Scheme 7. Oxidative Dissolution of Gold by Et₄TDS/I₂ in Acetone at Room Temperature with the Formation of Four Complexes by Varying the Molar Ratio of Et₄TDS to I₂^a

Two thioamide donors 3-methyl-benzothiazole-2-thione (mbtt) and 1-methyl-1H-benzimidazole-2(3H)-thione (mbit) were exploited to form dihalogen adducts. (56) Despite the similar structures of mbtt and mbit, their reactivities toward gold are totally different. The adduct mbtt·I₂ quantitatively dissolved gold powder at a molar ratio of gold to mbtt·I₂ of 1:2 at 25 °C within 3 days in anhydrous diethyl ether, whereas only 45% of gold was dissolved by mbit I₂ under the same conditions. Moreover, gold was oxidized to the +1 oxidation state by mbtt I₂ but to the +3 oxidation state by mbit I₂. The cationic gold complex [Au(mbtt)₂]I₃ was formed with mbtt, whereas with mbit, the anionic gold complex [(mtbiH)₂](AuI₄)I₃ was formed, which was not bound to any cationic 2-methylthiobenzimidazolium (mtbiH) unit but rather to iodides to form the square-planar [AuI₄]⁻ anion. The structures of mbtt, mbit, and mtbiH are shown in Scheme 3. The difference in reactivity of mbtt and mbit toward gold was attributed to the presence of the imido group that can form an intramolecular hydrogen bond with the S-bonded iodine atom (I_b) in the form of N–H···I_b. This new moiety might modify its reactivity with the gold surface.

The organic molecules dithiomalonamides (PhHN)₂DTM and Mo₂DTM (see Scheme 3) can react with iodine in organic solvent to form organic triiodides (OrgI₃), namely 3,5-bis(phenylamino)-1,2-dithiolylium triiodide ([(PhHN)₂DTL]I₃) and 3,5-bis(morpholino)-1,2-dithiolylium triiodide [Mo₂DTL]I₃. (55) These were applied for leaching of palladium from metal powders and model spent car exhaust catalysts at room temperature. Two more triiodides with tetrabutylammonium (N₄₄₄₄) and tetraphenylphosphonium (Ph₄P) cations were formed directly from the corresponding iodide salt with iodine, and they were studied for leaching of palladium as well. Actually, these two triiodides are trihalide ionic liquids, but due to their high melting point, they are solid at room temperature, so that they can only be used when dissolved in organic solvents. Therefore, we include them in this section rather than in section 5. The crystals obtained after dissolution of palladium metal were characterized by single-crystal X-ray diffraction and showed that the formed complex had the formula Org₂[Pd₂I₆] (Figure 6). The palladium recovery yields from spent car exhaust catalyst showed the trend following: [(PhHN)₂)DTL]I₃ > [Ph₄P]I₃ ≥ [N₄₄₄₄]I₃ ≫ KI₃. The aqueous KI₃ solution gave the lowest recovery yield, due to the formation of a passivation layer of PdI₂ on the palladium metal surface. The higher leaching yields of OrgI₃ compounds than KI₃ were ascribed to the formation of the Org₂[Pd₂I₆] complex which prevents formation of a passivation layer and facilitates its extraction in organic solvent. Note that [(PhHN)₂)DTL]I₃ gave a similar leaching yield as the most often studied adduct Me₂dazdt·2I₂ under the same experimental conditions (98 vs 99%). Gold can be oxidized by [(PhHN)₂)DTL]I₃ and [Mo₂DTL]I₃ as well, and the formed complexes have the stoichiometry Org[AuI₂]. Unlike for dissolution of palladium, the aqueous solutions of KI/I₂ have comparable efficiency as OrgI₃ solutions for dissolution of gold, because no occurrence of passivation was observed during the reaction.

Figure 6. Leaching of palladium from spent catalyst by organic triiodides in methylethylketone (MEK) under reflux for 7 days. Reprinted with permission from ref (55). Copyright 2017 American Chemical Society.

Organic iodide salts which provide both oxidative power and a coordinating ligand could dissolve gold with formation of organo-gold compounds. The iodide salts were iodocarbenium iodides (N,N-dimethyliodomethyleneiminium iodide) and bis-donor-substituted iodocarbenium iodide (bis(N,N’-dimethylamino)iodomethylene iodide and 2-iodo-1,3-dimethylimidazolium iodide) (Scheme 8). (63) Gold powder could be oxidized by iodocarbenium iodides in organic solvents (dichloromethane or acetonitrile) to form the gold(III)–carbene complex triiodo[(dimethylamino)methylene]gold(III) which was in equilibrium with gold(I) species iodo(dimethylamino)methylenegold(I) or [AuI₂(CHNMe₂)₂]⁺[AuI₂]⁻ (Scheme 8). The yield of gold(III) complexes was low and could be increased by addition of iodine, whereas bis-donor-substituted iodocarbenium iodide could also react with gold to form complexes with no need of addition of iodine. The mono- and bis-carbene-gold(III) complexes were produced (Figure 7). These reactions provide the routes for preparation of carbene complexes directly from metals.

Scheme 8. Structures of Iodocarbene Iodide and Gold Complexes Formed by Reaction between Compound (a) and Gold^a

Figure 7. Crystal structures of carbene complexes: the urea-derived complexes 10-mono (top, left, d_Au–C = 2.041(7) Å) and 10-bis (bottom, left, d_Au–C = 2.085(4) Å) and the corresponding NHC-complexes 11-mono (top, right, d_Au–C = 2.074(15) Å) and 11-bis (bottom, right, d_Au–C = 2.021(7) Å). Thermal ellipsoids at 50% probability. Reprinted with permission from ref (63). Copyright 2017 Wiley-VCH Verlag GmbH & Co. KGaA.

It can be concluded from this subsection that dihalogen adducts bearing S,S-donors or adducts on the basis of thioamide in organic solvents can oxidatively dissolve metals such as noble metals, cadmium, and mercury. The structure and the chelating properties of the organic adducts play an important role in the oxidation reactions. The same adducts can form different crystal structures after oxidation reaction with different metals as shown in Figure 5. In addition, by slightly adjusting the structure of the organic adducts, their oxidizing capability could be changed. For example, [Me₂Pipdt]I₃ can oxidize platinum, whereas Me₂dazdt·2I₂ cannot. The dihalogen adducts also provide the possibility to form organo-gold compounds directly from metals as shown in Figure 7. Moreover, the organic lixiviants are sometimes more efficient than the aqueous lixiviant for oxidative dissolution of metals. (55) Dihalogen adducts are claimed to be safe, cheap, easy to handle, and noncytotoxic. However, most of the organic compounds are destroyed in order to recover the metals after dissolution, so that these organic compounds cannot be reused. Therefore, economic analysis should be performed prior to large scale applications.

3. Halocarbons as Oxidizing Agent

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Organic halides (halocarbons) can act as oxidizing agents in polar organic solvents and have been used for dissolution of metals with the aim of direct synthesis of metal complexes. Tezuka et al. studied the oxidative dissolution of copper by halocarbons in dimethyl sulfoxide (DSMO) with the formation of the complex CuCl₂(DMSO). (64)

Both the halocarbon and the polar solvent played an important role in the dissolution process. The most studied halocarbon was carbon tetrachloride (CCl₄), but other halocarbons could be used as oxidizing agents as well, such as diphenyldichloromethane, dichloroacetic acid, or trichloroacetic acid esters and bromoalkanes (e.g., carbon tetrabromide). DMSO could not be replaced by other polar organic solvents, such as methanol, tetrahydrofuran, benzene, chloroform, acetonitrile, or pyridine. The dissolution mechanism is described by eqs 7–9. First, copper is oxidized by CCl₄-DMSO with the formation of CuCl₂(DMSO)₂ and dichlorocarbene (:CCl₂). The dichlorocarbene instantaneously reacts with DMSO to produce dimethyl sulfide and phosgene. Phosgene directly reacts further with copper to form CuCl₂(DMSO)₂ and carbon monoxide.

(7)

(8)

(9)

Dimethylacetamide (DMAA) could replace DMSO for copper dissolution by CCl₄ as oxidizing agent. The difference compared to the CCl₄-DMSO system is that copper is oxidized to copper(I) by CCl₄ in DMAA with the formation of C₂Cl₆. The formed copper(I) complexes are slowly oxidized by CCl₄-DMAA or air to copper(II) complexes. (65) Similar as in the CCl₄-DMSO system, copper is dissolved in CCl₄-DMAA via a radical mechanism, but the formed radical is CCl₃ rather than :CCl₂. The results showed that the oxidation of copper is a surface chemical reaction, with the interaction of the adsorbed organic compounds with the metal surface as the rate-limiting step.

A similar radical mechanism of oxidative dissolution of titanium was observed by Egorov et al. for the use of benzyl bromide as oxidizing agent in the presence of the polar solvent DMF. (66) Analysis of the reaction products in the presence of radical scavengers dicyclohexyldeuterophosphine and in their absence suggested that the reaction occurs via the benzyl radical (·CH₂–C₆H₅). Under oxygen-free conditions, the dissolution of titanium occurs by a one-electron transfer mechanism, with formation of 1,2-diphenylethane and titanium(IV) complexes. The complex [TiBr(DMF)₂]Br₂ is initially formed but slowly reacts further with benzyl bromide and DMF to yield the complex [TiBr(DMF)₅]Br₃. Note that titanium is not oxidized by benzyl bromide in DMF in the presence of oxygen, probably because of the formation of a passivating oxide film on the metal surface, which prevents contact between the metal surface and the oxidizing agent.

CCl₄ in ammonia solutions can dissolve copper under very mild conditions with formation of [Cu(NH₃)_m]Cl₂·nH₂O. (67) At the same time, CCl₄ is decomposed to CH₂Cl₂. The reaction is believed to have the same radical mechanism as in DMSO, with the formation of intermediate :CCl₂. Eight additional halogenated compounds were tested for copper dissolution in the presence of ammonia solution: CHCl₃, CHBr₂CHBr₂, CH₂Br₂, CH₃CCl₃, CHCl₂CHCl₂, CH₂ClCHCl₂, CCl₂CCl₂, and CH₂ClCH₂Cl. More copper could be dissolved in ammonia solutions upon addition of the first four compounds and CCl₄, whereas less was dissolved by adding the last four halogenated compounds. Among the nine halogenated compounds and NH₃(aq), CCl₄ is the best compound to solubilize copper. Although without CCl₄, ammonium solution can dissolve copper as well, addition of CCl₄ can speed up the reaction by a factor of 150. This system CCl₄–NH_3(aq) has different oxidizing power toward different metals. For example, zinc can be dissolved with an efficiency of 60% relative to copper. Less than 0.5% of silver and tin can be dissolved, but lead and iron do not react. This difference might be due to the different coordinating behaviors of metals with ammine ligands.

Halocarbons in organic solvents can even dissolve noble metals. (68) The studied leaching systems contain halocarbon compounds used as oxidizing agents including CCl₄, CBr₄, CPh₂Cl₂, CPhCl₃, and C(CN)₂Cl₂, and coordinating organic solvents including DMSO, DMF, and DMAA. The results for dissolution of various noble metals by different leaching systems are summarized in Table 3. Different combinations of oxidizing agents and solvents gave different behavior for metal dissolutions. It was proposed that the reaction proceeds through a carbene intermediate, similarly to the reaction between copper and CCl₄–DMSO. Moreover, dissolution of the oxides, sulfides, tellurides, and selenides of noble metals (e.g., PdO, PtO₂, PtS₂, Ag₂S, Ag₂Se, and Ag₂Te) was studied as well by this type of leaching system. (68)

Table 3. Dissolution of Noble Metals in Mixtures of Halocarbons with Organic Solvent (68)

Metal	Lixiviant	Temp (°C)	Reaction product
Ag	CCl₄–DMSO	80	AgCl₂^–
	CBr₄–DMSO	80	AgBr₂^–
	CPh₂Cl₂–DMAA	110	AgCl₂^–
Au	CBr₄–DMSO	^a	AuBr₄^–
Pd	CCl₄–DMSO	^a	PdCl₂·2DMSO
	CBr₄–DMF	^a	PdBr₂·2DMF
	CPh₂Cl₂–DMAA	110	PdCl₂·2DMAA
	CPh₂Cl₂–thiophene	^a	PdCl₂·2(C₄H₄S)
Pt	CPh₂Cl₂–DMAA	110	PtCl₂·2DMAA
	C(CN)₂Cl₂–DMF	100	PtCl₂·2DMF
Rh	CPh₂Cl₂–DMAA	110	RhCl₃·3DMAA
	C(CN)₂Cl₂–DMF	100	RhCl₃·3DMF
Ru	No studied system could dissolve Ru

^{^a}

Temperature was not reported.

An aqueous mixture of the halocarbon N-bromosuccinimide (NBS) and the coordinating solvent pyridine (Py) could dissolve gold. (1) The leaching yield of gold with NBS/Py was higher than that with the classic cyanide method, with thiourea, and with solutions of KI/I₂. NBS/Py also had good leaching selectivity for gold over other metals coexisting in the gold ore such as Fe, Al, Mg, Cu, and Zn (Figure 8). The oxidation by NBS involved mainly the release of a molecular bromine intermediate that oxidizes gold to form the anion complex [AuBr₄]⁻, which subsequently reacted with a pyridine molecule to form PyAuBr₃. The metal coordination with a pyridine-like unit decreased the redox potential for oxidation of metallic gold by NBS. Due to the exothermic reaction, the dissolution of gold proceeds better at lower temperatures, as indicated by the fact that the leaching yields of gold at 70 and 50 °C were much lower than the yield at 25 °C.

Figure 8. Gold leaching from ores by N-bromosuccinimide/pyridine (NBS/Py). (a) Scanning electron microscopy (SEM) image of the gold ore; (b) corresponding metal contents in the raw gold ore; (c) effect of pH on the leaching yield of gold by different methods; (d) effect of pH on the leaching yields for the collective metals contained in the gold ores. The NBS and pyridine concentrations were 10 and 100 mm, respectively. Reprinted with permission from ref (1). Copyright 2017 Wiley-VCH Verlag GmbH & Co. KGaA.

Stabilized bromine compounds such as 1-chloro-3-bromo-5,5-dimethylhydrantoin (GEOBROM 3114) and 1,3-dibromo-5,5-dimethylhydantoin (GEOBROM 5500) (Scheme 9), which have lower vapor pressures than bromine, can dissolve gold as well. (69) During the leaching of gold in GEOBROM 5500 media, gold is oxidized anodically to the auric state, while GEOBROM 5500 is cathodically reduced to the very effective oxidizing agent hypobromous acid. Subsequently, gold goes into solution as the tetrabromoaurate(III) complex, [AuBr₄]⁻, which has a very high formation constant (10³²) in aqueous solutions. Different metals and minerals can either decrease or increase the dissolution rate of gold in bromine media by galvanic interactions. (69) For example, copper, iron, and galena decrease the dissolution rate of gold, due to the galvanic interaction between the two substances. Sphalerite can enhance the dissolution rate of gold significantly. This can probably be attributed to the action of dissolved Zn(II) ions on the surface of gold and the formation of a film (probably a zinc complex) on a gold surface which can increase its conductivity.

Scheme 9. Chemical Structures of GEOBROM 3114 (left) and GEOBROM 5500 (right)

It is shown in this section that various halocarbons could be used as solvent in leaching systems for dissolution of metals. However, most halocarbons are toxic, especially CCl₄. Due to the suspected carcinogenicity of CCl₄, the use of this solvent has been banned in many countries. Therefore, alternative green leaching systems should be developed for future use.

4. Donor–Acceptor Electron-Transfer Systems

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In a donor–acceptor electron-transfer system, neither the donor nor the acceptor alone directly reacts with metals, but their mixtures do, because new species capable of oxidizing metals are generated by the interaction between the donor and the acceptor. Examples are mixtures of DMSO and ammonium halides (NH₄X), DMSO and HX (X = Cl, Br, and I), and DMSO and SO₂ and a mixture of thionyl chloride (SOCl₂) and pyridine (organic aqua regia).

4.1. DMSO with Halide Acids or Salts

The DMSO–halide acids (HX, X = Cl, Br, I) in both aqueous and organic systems have been studied for oxidative dissolution of metals such as copper, silver, gold, palladium, and platinum. (70−73) The final products of the reaction between DMSO and HX are mainly dimethyl sulfide (Me₂S), dihalogens, and water, together with some byproducts such as CO and CS₂. The intermediate products Me₂S(OH)X, Me₂S·X₂, and X₂ are most likely responsible for the oxidation of metals. The sequence of reactions between DMSO and HBr is presented in Scheme 10:

Scheme 10. Sequence of Reactions between DMSO and HBr

Various metal complexes can be synthesized by dissolution of the corresponding metals in DMSO–HX solutions. For example, after adding palladium to the mixture of DMSO and HBr, the solid product Me₂SPdBr₂ was isolated. The liquid phase is most likely a mixture of several complexes, depending on the ratio of the components. By dissolving silver in the system of DMSO–HBr, several silver complexes, e.g. AgBr, [Me₃S]AgBr₂, and [Me₃S]Ag₂Br₃, were formed. Whereas in the system of DMSO–HX–ketone (X = Br, I; ketone = acetone, acetylacetone, or acetophenone), the complexes formed were [Me₂S⁺CH₂COR]AgX₂^– (R = Me, Ph; X = Br, I). The composition of the complexes depended on various factors, including the DMSO-to-HX molar ratio, the nature of HX, and the methods used to isolate the solid products from the solution. It is noteworthy that silver does not dissolve in the DMSO–HF system and that it dissolves only very slowly in the DMSO–HCl system. This is probably due to the stronger reactivity of the formed complex with bounded molecular fluorine or chlorine toward organic molecules than to metals. The reactions between DMSO and HCl are shown in Scheme 11.

Scheme 11. Reactions between DMSO and HCl

The dissolution of copper was investigated in the system of DMSO–HX (X = Br, Cl). HX was dissolved in water or organic solvents: acetonitrile (MeCN) and nitrobenzene (PhNO₂). (73) The dissolution rates of copper metal in nonaqueous media are 1 order of magnitude higher than in aqueous media, following the sequence: H₂O < MeCN < PhNO₂. This difference in reactivity was attributed to a change in the adsorbability of the reagents on the metal surface. The low reactivity of the aqueous system is caused by the strong adsorption of water on the metal surface, which competes with the oxidizing species for contacting with the metal surface. A distinctive feature of metal dissolution in the DMSO-HBr_aq system is the presence of two or three maxima in the plot of the metal dissolution rate as a function of the molar fraction of HBr, indicating that several species that can oxidize metals are formed upon the interaction of DMSO and HBr. Besides bromine-containing compounds, oxygen-containing compounds (H₂O₂, HXO) are formed as well, due to the interaction between DMSO and HX in aqueous solutions. (72) DMSO-HX_aq dissolves both transition metals (Cu) and noble metals (Au, Ag, and Pt), whereas gold is insoluble in the nonaqueous system DMSO–HCl_solv. Therefore, the latter system can be used for selective dissolution of copper in the presence of gold.

The alternative system DMSO–NH₄X_aq can dissolve copper as well. (74) The mechanism for the formation of intermediates active for metal dissolution shown in Scheme 12 is similar to that for the system DMSO–-HX.

Scheme 12. Reactions between DMSO and NH₄X

Moreover, the dissolution rate of copper in air is faster than that in argon, indicating that molecular oxygen probably can react with the intermediate species to form a new species that can oxidize the metal. In the DMSO–HX system, nonaqueous solutions are more reactive toward metals than aqueous solutions. However, copper dissolves faster in NH₄I_aq-O₂ containing no DMSO than in DMSO–NH₄X_aq. This was explained by the formation of the stronger oxidizing agent IO₃^– in the former system.

4.2. DMSO with SO₂

The mixed nonaqueous system DMSO–SO₂ has shown to have good potential for dissolution of metals. (75−82) The metals Mg, Sr, Ba, V, Mn, Fe, Co, Ni, Cu, Zn, Al, In, Pb, and Yb dissolve in DMSO–SO₂ to form metal disulfates (M_x(S₂O₇)_y·zMe₂SO), and the metals Sr, Ba, and Pb react as well with formation of metal sulfates which form a passive layer on the metal surface. Chromium is completely inert in the mixed solvent. Other metals, Na, Be, Ca, Ce, Pr, Eu, Dy, Ga, TI, Sn, Sb, Bi, I, and Cd, also react, but the reaction products have not been characterized yet. These metals dissolve neither in DMSO nor in SO₂ separately, but they do dissolve in the mixture of DMSO and SO₂. Adducts with compositions 2SO₂·DMSO, SO₂·DMSO, and SO₂·2DMSO have been identified by Raman spectroscopy and phase study (i.e., by measuring the eutectic point for mixtures of SO₂ with DMSO to obtain the structure of adducts). (81,83) These adducts are considered as active intermediates for metal oxidation. Dimethyl sulfide is one of the reaction products, and the existence of the radical ion [SO₂]^•– and an ion pair containing a metal ion and [SO₂]^•– have been demonstrated. (79) The adduct 2SO₂·DMSO provides a starting point for the formation of a radical ion containing the S–O–S group, [DMSO·OS·O·SO₂]^•–. By stepwise reaction with DMSO, the disulfate anions are formed via a series of successive radical anions.

Besides DMSO, other solvents containing SO₂ have been tested for dissolving metals such as Li, Na, Mg, Ca, Fe, and Zn. The solvents DMAA, DMF, formamide, ethanol, water, trimethyl phosphate, and tris(dimethylamino)phosphine oxide react with metals, whereas the solvents tetrahydrothiophen-1,1-dioxide, nitrobenzene, nitromethane, ethyl acetate, acetonitrile, diethyl ether, 1,4-dioxane, tetrahydrofuran, pyridine, and acetone do not. The solvent must have a high dielectric constant (ε > 20), as well as a high Gutmann donor number (DN > 20) for spontaneous dissolution of metals to occur. A solvent with a high dielectric constant is required for the formation of the sulfoxylate radical ion. A solvent with a high donor number is required for the solvation of metal ions with inhibition of recombination of metal ion and [SO₂]^•– to form metal and SO₂. The reaction product after metal dissolution is a metal dithionite rather than a sulfate or disulfate. (81) The dithionite anion is formed by direct dimerization of the radical ion [SO₂]^•–.

4.3. Organic Aqua Regia

“Organic aqua regia” was first reported by Lin and co-workers in 2010, and it can dissolve gold and palladium with a high dissolution rate at room temperature. (84) It is a mixture of SOCl₂ and a polar organic solvent such as pyridine (Py), DMF, or imidazole. It was named as “organic aqua regia”, because of its similarity to aqua regia: (1) it can dissolve noble metals; (2) noble metals cannot dissolve in either of the components, and only their mixtures are strongly oxidizing. The mixture SOCl₂–Py can dissolve gold at a rate of 0.3 mol m^–2 h^–1 at room temperature, which is faster than the dissolution of gold in conventional cyanide leaching agents (<0.004 mol m^–2 h^–1) and iodide solutions (<0.16 mol m^–2 h^–1). The enhanced reactivity of organic aqua regia is ascribed to the formation of the adduct SOCl₂·Py, resulting from the charge-transfer interaction between SOCl₂ and Py. The sulfur atom in SOCl₂ acts as an electron acceptor, and the nitrogen atom in pyridine acts as an electron donor. Gold dissolves in the solution in the form of [AuCl₄]⁻ rather than AuCl₃ or its complex with pyridine.

Organic aqua regia can be formed not only with pyridine but also with other polar organic solvents. (85) The following solvents or organic compounds have been found to be able to effectively dissolve gold in the presence of SOCl₂: pyrrole, pyrrolidine, pyrrolidone, isoxazole, isothiazole, pyrazole, imidazole, thiazole, oxazole, pyrazolone, bipyrazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, indole, quinoline, purine, pteridine, phthalocyanine, N,N’-dicyclohexylcarbodiimide, DMF, N,N’-dimethylbenzylamine, dodecyltrimethylammonium bromide, trip-tolyl-phosphine, etc. However, effective dissolution of gold in a mixture of SOCl₂ with any of the following chemicals has not been observed: maleimide, azobis(isobutyronitrile), aniline, polyaniline, phenanthroline, methylbenzyl cyanide, 2-acetyl-1-methylpyrrole, and benzyltriethylammonium tetrafluoroborate.

A qualitative study has shown that copper, iron, nickel, tin, indium, silver, and palladium dissolve in the SOCl₂–Py mixture, whereas platinum, titanium, tungsten, tantalum, and chromium do not. (85) The fact that some metals cannot be dissolved in SOCl₂–Py is probably due to surface passivation.

By varying the composition of organic aqua regia, selective dissolution of noble metals can be achieved. For example, by replacing pyridine with DMF, the mixture SOCl₂–DMF can dissolve gold but not palladium or platinum. A mixture of SOCl₂–pyridine (3:1) can dissolve gold, silver, and palladium at room temperature, while platinum is completely inert, even at 70 °C (reflux) for 1 week. Therefore, selective dissolution of gold, palladium, and platinum on a silicon substrate could be achieved by first dissolving gold in SOCl₂–DMF, followed by dissolution of palladium in the SOCl₂–pyridine mixture (Figure 9). It is assumed that selective dissolution is caused by differences in interaction between SOCl₂ and the organic solvent.

Figure 9. Illustration of selective dissolution of gold, palladium, and platinum in *organic aqua regia*. A silicon substrate was metallized with a Pd/Au/Pt layer (250 nm thick each by electron-beam evaporation or direct current sputtering, with chromium used as the adhesion layer). The top row of images shows the photographs of the Pd/Au/Pt metallization layer on a silicon substrate during the process of selective dissolution. Reprinted with permission from ref (84). Copyright 2010 WILEY-VCH Verlag GmbH & Co. KGaA.

Besides the application in the recovery of noble metals, organic aqua regia can be applied in the microelectronic industry, for instance for “vapor” etching of gold metallization on a circuit board by vaporized organic aqua regia. (84) Etching of copper from the fabrication of printed circuit boards has been studied by using the SOCl₂–CH₃CN solutions as etchant at room temperature. The etching rate was found to be much faster than any currently used etchant for copper. (85) Subsequently, this solvent was successfully applied for the separation of platinum from a mixture of gold and platinum nanoparticles and from a Au/Pt core–shell nanoparticle catalyst, with the purity of the recovered platinum above 95%. (86) This organic aqua regia was also applied in organic synthesis, for activation of gold/activated-carbon catalysts for hydrochlorination of acetylene. (87) Activation of gold/activated-carbon catalyst in organic aqua regia improves the activity and stability of the catalyst compared to the activation procedure in conventional aqua regia.

Organic aqua regia can oxidize noble metals under mild conditions, but the employed reagents are hazardous, which makes this reagent less attractive from an environmental point of view, and this leads to a further search for safer alternatives for aqua regia.

5. Ionic Liquids and Deep Eutectic Solvents

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5.1. Ionic Liquids

Ionic liquids (ILs) are solvents that are composed entirely of ions, and some of them can be considered as environmentally friendly solvents. They have been applied as alternatives for molecular organic solvents in various fields, due to their unique properties such as a negligible vapor pressure, a wide liquid range, high thermal and chemical stability, a wide electrochemical window, and poor flammability. (88−93) The properties of ILs can be tuned by changing the structure of organic cations and inorganic or organic anions. For example, ILs with oxidizing power can be synthesized by adding molecular halogens to halide ILs so that tri- or polyhalide or interhalide ILs can be formed, such as [Cl₃]⁻, [Br₃]⁻, [I₃]⁻, [ClBr₂]⁻, [BrCl₂]⁻, and [BrI₂]⁻. (94−98) The polyhalide ILs are most often used as reagents for halogenation of organic compounds, such as aromatics, alkenes, and alkynes, (99−101) but they can be used for oxidative dissolution of metals or alloys as well. (15,94,95,102,103) These polyhalide ILs can be used in pure form or as mixtures with halide ILs for dissolution of metals.

5.1.1. ILs as Oxidizing Agents

Trihalide ILs can be prepared by simply mixing equal molar amounts of halogens and halide ionic liquids. They can safely store halogens and in the meantime have oxidizing properties. Various metals can be dissolved in trihalide ionic liquids under mild conditions. The mixtures of trihalide and halide ILs work as well. In this case, halide ILs act as solvent and trihalide ILs as oxidizing agent. A series of trichloride ILs that are liquid form at room temperature was synthesized by Li et al. (94) The cationic cores used were phosphonium, ammonium, pyridinium, pyrrolidinium, and imidazolium (Scheme 13), and the full names and abbreviations of the cations are shown in Table 4. It was confirmed by NMR spectroscopy that all the studied cations are stable in the presence of chlorine, except imidazolium cations. The trichloride ILs have a lower viscosity and melting point than the corresponding chloride ILs, due to the more extended charge delocalization in the trichloride anions compared to the chloride anion, and thus weaker electrostatic interactions between cations and anions. A total of 12 metals and two metal alloys have been tested for dissolution in the representative trichloride IL [P_444,14][Cl₃]: Fe, Cu, In, Zn, Ga, Sb, Au, Pt, Ge, Ta, Sm, Dy, GaAs, and InAs. (94) All metals and alloys, except Sm (5 mm pieces), Dy (5 mm pieces), Ta (powder), and Pt (wires) could be dissolved in this trichloride IL at room temperature. Thus, trichloride ILs can selectively dissolve some metals and, for example, allow the separation of the highly valuable gold and platinum. The fact that samarium metal did not dissolve in the trichloride ILs was unexpected, because rare-earth metals are in general very reactive. In follow-up experiments using freshly milled samarium powder instead of samarium metal pieces, different results were obtained: samarium powder could indeed be oxidatively dissolved in trichloride ILs. (15) This result showed that samarium metal pieces are difficult to dissolve in trichloride ILs because of the presence of a protective oxide layer on the samarium metal surface which prevents contact between the oxidizing trichloride anion and the metal.

Scheme 13. Structure of Cations of Trichloride ILs^a

Table 4. Full Names and Abbreviations of the Cations of Trichloride ILs

Name of IL cation	Abbreviation
Trihexyl(tetradecyl)phosphonium	P_666,14
Tetrabutylphosphonium	P₄₄₄₄
Tributyl(tetradecyl)phosphonium	P_444,14
1-Butylpyridinium	BPy
Methyltrioctylammonium	N₁₈₈₈
1-Butyl-1-methylpyrrolidinium	BMPyrr
1-Butyl-2-methylpyridinium	2-MBPy
1-Butyl-1-methylpiperidinium	BMPip
1-Butyl-4-methylpyridinium	4-MBPy
1-Hexylpyridinium	HPy
1-Butyl-3-methylimidazolium	Bmim
1-Decyl-3-methylimidazolium	Dmim

Metal recovery from spent samarium–cobalt (Sm–Co) magnets using a trichloride ionic liquid was studied by the same group. (11) The results showed that Sm–Co magnets, containing Fe, Co, Cu, and Sm, can be quantitatively dissolved in trichloride ILs. Two processes are involved in oxidative dissolution: oxidation of the metals by trichloride ions and dissolution of the oxidation products in the ionic liquid. The oxidation process converts the metals to the corresponding metal chlorides, and simultaneously each trichloride anion is reduced to three chloride ions. The generated metal chlorides are subsequently dissolved in the IL by complex formation. Thus, the dissolution mechanism of Fe, Co, Cu, and Sm in the trichloride IL [P_666,14][Cl₃] in the presence of coordinating chloride ions can be expressed by the following equations:

(10)

(11)

(12)

(13)

More trihalide or tri-interhalide ionic liquids with a tributyldecylphosphonium cation ([P₄₄₄₁₀]) and various anions have been prepared, including trichloride ([Cl₃]), bromidedichloride ([BrCl₂]), chloridedibromide ([ClBr₂]), tribromide ([Br₃]), iodidedibromide ([IBr₂]), bromidediiodide ([BrI₂]), and triiodide ([I₃]). (95) One representative IL, [P₄₄₄₁₀][Br₃], was selected for oxidative dissolution tests for metals. Several base metals and metalloids (iron, zinc, copper, cobalt, bismuth, indium, tin, gallium, antimony, and germanium) can be oxidatively dissolved in [P₄₄₄₁₀][Br₃], as well as the noble metals palladium and gold. However, platinum and rhodium could not be dissolved, similarly to what was observed for the trichloride IL [P_666,14][Cl₃]. (94) Copper as a representative metal could be efficiently dissolved in all the synthesized trihalide ILs, suggesting that all these the trihalide ILs can oxidize metals. The same tribromide IL [P₄₄₄₁₀][Br₃] could also efficiently leach gallium, indium, and arsenic from semiconductors (GaIn, GaAs) and light-emitting diodes that contained GaAs. (103)

May and co-workers studied the reaction of the interhalide IL 1-hexyl-3-methylimidazolium iodide dibromide ([Hmim][Br₂I]) with copper, silver, and gold, investigated by using X-ray photoelectron spectroscopy, mass loss measurements, and gas-phase mass spectrometry. (104) All the studied metals can be oxidized by the interhalide IL to form molecular iodine and metal ions in the +1 oxidation state, in the form of [Br–M–Br]⁻ (M = Cu, Ag, and Au), which is different from dissolution of metals in trichloride ILs, where the metals are oxidized to their highest oxidation state. (94) The reaction can be described as eq 14:

(14)

The dissolution behavior of gold in 1-hexyl-3-methylimidazolium dibromoiodide [Hmim][Br₂I] and 1-butyl-2,3-dimethylimidazolium dibromoiodide [C₄C₁C₁Im][Br₂I] that was methylated at the 2-position of the imidazolium ring was compared, and this study rules out the formation of imidazole-carbene as a cause of the oxidation reaction. Moreover, the oxidation reaction is not sensitive to either water or air. The dissolution efficiency of gold in aqueous solutions of Na[Br₂I] is at least ten times less than that in [Hmim][Br₂I], indicating that the organic cation [Hmim]⁺ plays an important role in the dissolution of the formed metal complex.

Recently, ILs with a poly pseudohalide anion such as [Br(BrCN)]⁻ and [Br(BrCN)₃]⁻ were synthesized and successfully used for dissolution of gold. (105) The vapor pressures of the poly pseudohalogen salts bis(triphenylphosphoranylidene)iminium bromide [PNP]Br are reduced by at least a factor of 10 to 0.1 mbar (1 equiv BrCN) and 15.5 mbar (5 equiv BrCN) at ambient conditions, compared to the vapor pressure of toxic BrCN (160 mbar at 25 °C). Room temperature ILs can be obtained when more than 3 equiv of BrCN is added to bromide salts. Due to the significantly lower vapor pressures, the poly pseudohalide ILs can easily be handled and applied, for example, in metal recycling. A room temperature IL was formed by adding 4 equiv of BrCN to the IL butyldiethylmethylammonium bromide. This IL can dissolve gold with the formation of gold(I), as well as predominantly gold(III) cyanido and gold(III) bromidocyanido species.

Due to the involvement of halogens in ILs, the polyhalide ILs have oxidizing power and hence can be used as both oxidizing agent and solvent. However, ILs without oxidizing power can be applied as solvents for metals dissolutions together with some oxidizing agent, e.g. trihalide ILs in halide ILs as solvents.

5.1.2. ILs as Solvents

Whitehead and co-workers reported a series of studies where ILs were used as solvents for recovery of gold and silver from ores. (106−108) Recovery efficiencies of metals were studied by varying solvent ILs and oxidizing and complexing agents. The IL [Bmim][HSO₄] was extensively studied for metal extraction due to its acidity. The system of [Bmim][HSO₄]/thiourea/Fe₂(SO₄)₃ could effectively leach gold and silver with high selectivity over the base metals Cu, Zn, Pb, and Fe in a gold-bearing ore. (106) Here the IL acts as solvent and Fe₂(SO₄)₃ as oxidizing agent. Thiourea was selected as complexing agent because of its high selectivity for gold and silver. This IL system and the aqueous system of H₂SO₄/thiourea/Fe₂(SO₄)₃ have similar capability for leaching of gold. However, this IL system has higher leaching efficiency of silver than the aqueous system, because in the aqueous system, insoluble silver species precipitate and form a passivation layer on the silver metal surface. An additional benefit was that the IL could be recycled. HSO₄-based ILs with different 1-alkyl-3-methyl-imidazolium cations (alkyl = n-butyl, n-pentyl, n-hexyl, n-heptyl, and n-octyl) could also be used as solvents, but as the alkyl chain length was increased, the efficiency of gold recovery dropped, probably due to the higher viscosity of the ILs. (108) Bmim-based ILs with varying anions (N(CN)₂^–, CH₃SO₃^–, HSO₄^–, BF₄^–, and Cl^–) were used as solvent for recovery of gold and silver, but among all five ILs investigated, only [Bmim][HSO₄] showed high extraction efficiency and selectivity (Figure 10). The selectivity differences between different anions result from their differences in coordination ability with metal ions.

Figure 10. Extraction of gold and silver (top) and base metals (bottom) from a complex sulfidic gold-bearing ore using thiourea leaching with ILs with the [Bmim]⁺ cation and different anions (50 °C, 48 h leaching). Reprinted with permission from ref (108). Copyright 2007 Elsevier B.V.

Apart from Fe₂(SO₄)₃, also peroxomonosulfate (HSO₅^–) was tested as oxidizing agent for leaching of gold, silver, and base metals from ores in the ILs [Bmim][HSO₄] and [Bmim]Cl, with various complexing agents (thiourea, NaCl, NaBr, and NaI). (107) All the components in the lixiviant play important roles, because changing either the solvent, the oxidizing agent, or the complexing agent changes the leaching efficiency, sometimes even dramatically. The best combination for leaching gold and silver is the system [Bmim]Cl/NaI/HSO₅^–, which can quantitatively leach silver and 85% of gold, with only limited codissolution of base metals. This selectivity was attributed to formation of the stable gold iodo complex and the soluble silver iodo complex in the ionic liquid environment.

By studying the electro-oxidation of iodide on a gold electrode in the room temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, Bentley et al. observed that gold could be oxidized in the presence of iodide. (109) Coulometric/electrogravimetric analysis suggested that the oxidation state of the soluble gold species is +1 and that diiodoaurate, [AuI₂]⁻, is the most likely intermediate compound. A proportionally smaller amount of triiodide intermediate was also detected by means of UV–vis absorption spectroscopy. On this experimental evidence, it was proposed that iodide oxidation of gold occurs via two parallel reaction pathways: predominantly via a diiodoaurate intermediate (eqs 15 and 16) and to a lesser extent via a triiodide intermediate (eqs 17 and 18).

(15)

(16)

(17)

(18)

ILs were used as electrolytes in the electrochemical process for oxidative dissolution of platinum. (110) Bmim-based ILs with various anions were tested for anodic dissolution of platinum, namely, Cl^–, Br^–, I^–, [SCN]⁻, and [N(CN)₂]⁻. Only IL with chloride anions could dissolve platinum. Platinum dissolution was observed in [Mim]Cl and [Bmim]Cl, but not in [Hmim]Cl at 80 °C, but all these three ILs could dissolve platinum at 150 °C. The platinum dissolution rate in [Bmim]Cl at 80 °C is of the same order of magnitude as in aqua regia at 25 °C. A mixture of Bmim-based ILs with bis(trifluoromethanesulfonyl)imide ([NTf₂]) and chloride anions could also dissolve platinum, but the dissolution rate and the amount of dissolved platinum were lower than those in pure [Bmim]Cl. This mixture could leach platinum immobilized on the carbon substrate of the electrodes from fuel-cell membrane electrode assemblies and simultaneously electrodeposit platinum on the counter electrode. The electrochemical dissolution of platinum was achieved in eutectic-based ILs, ZnCl₂-1-ethyl-3-methylimidazolium chloride (molar ratio: 1:3) and ZnCl₂-chloline chloride (molar ratio 1:1), with formation of [PtCl_x]^y−. (111)

Although ILs are considered as environmentally benign reagents and although they can efficiently dissolve various metals under mild conditions, they are in general quite expensive, so that they cannot be used in an economically way to dissolve base metals. However, the high cost of ILs can be justified for the extraction or recovery of precious metals from mineral ores or secondary resources.

5.2. Deep-Eutectic Solvents

Deep-eutectic solvents (DESs) are considered as ionic-liquid-analogues in the literature, because DESs and ILs have quite similar properties. For example, they both have low vapor pressure, have a relatively wide liquid-range, and are often nonflammable. However, they are two different types of solvent. ILs are pure compounds that are composed of one type of cation and only one type of anion, whereas DESs which are formed from a eutectic mixture of Lewis or Brønsted acids and bases contain a variety of anions and cations. DESs can be formed by combination of an organic salt (e.g., ammonium halide and imidazolium halide) with a metal salt or hydrogen-bond donor. The majority of studies in the literature have focused on the system comprising choline chloride (hydroxyethyltrimethylammonium chloride), because choline chloride is a nontoxic and cheap compound. More detailed information on DESs and their applications can be found in a review paper in this journal. (112)

Generally, DESs have no oxidizing power themselves, so they are often used as solvents for metal dissolution either with the aid of an oxidizing agent or as an electrolyte for electrooxidation of metals (electrolytic dissolution). The behavior of metals (for example the redox potential of ion couples) in DESs and ILs is different from that in aqueous solutions. Iodine in DESs (e.g., in Ethaline which is a mixture of choline chloride and ethylene glycol in a 1:2 molar ratio) shows strong oxidizing power which can be used for leaching of gold from gold-bearing ores and from SEM samples where gold had been coated on the surface of the sample to minimize charging effects. (17,113) In this case, iodine in DESs used for metal dissolution is similar to the halogens in organic solvents systems, since DESs and organic solvents are both used as solvent for halogen and the formed metal salts. The difference is that most DESs have components that can act as ligands, whereas most organic solvents are much less coordinating. For example, the chloride ions in Ethaline can complex with gold to form [AuCl₄]⁻, and this complex can dissolve in DESs easily by interacting with the countercation choline.

DESs can be used as an electrolyte for dissolution of metals via an electrochemical process, such as anodic dissolution and electropolishing of metals. (114,115) DESs as electrolytes have several advantages (e.g., nonacidic formulation, improved surface finish on cast pieces, and improved current efficiency) compared to conventional electrolytes such as concentrated phosphoric acid and sulfuric acid mixtures. Metal polishing is to dissolve a metal surface controllably to reduce the surface roughness. Electropolishing of stainless steel was realized in Ethaline. (114) Differently from conventional electropolishing in aqueous solutions, the metal dissolved in DESs without prior passivation and no gas was observed at the anode surface. A pilot-scale unit for electropolishing of Series 300 stainless steel and other nickel-containing alloys was built and operated by the IONMET consortium. (116)

6. Other Oxidizing Agents

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6.1. Oxygen Gas

Gold can be effectively oxidized by oxygen gas in the presence of cetyltrimethylammonium bromide to form [AuBr₄]⁻ complex, with the aid of ultrasound. (117) The ligand is crucial as it assists the oxidation process and stabilizes the formed Au(III) cation. Sonication is a must for this process because it can continuously provide oxygen to the solution. In the absence of sonication, no observable reaction occurred, even after several days. Barnartt et al. investigated the reactivity of 23 metals with acetylacetone in the presence or absence of oxygen gas. (118) Acetylacetone is the conjugated acid of the acetylacetonate anion, a bidentate ligand that forms chelate complexes with many metals. It was found that 10 metals have an appreciable reaction rate with acetylacetone in the presence of oxygen gas, namely Pb, Mn, Zn, Mg, Cd, Fe, Cu, Co, In, and Sn, whereas another 13 metals show no reactions (Ti, Zr, V, Nb, Ta, Cr, Mo, W, Ni Al, Si, Ge, and Sb). Besides the oxygen-absorption reaction, Mg, Mn, and Zn react with acetylacetone in the absence of oxygen gas, with evolution of hydrogen gas. The reactions of metals with acetylacetone in the presence or absence of oxygen gas are

(19)

(20)

where HA is acetylacetone and x and y are the valence of the metal.

It is evident that pure acetylacetone can react or etch metal surfaces. However, side reactions were observed in the presence of oxygen gas, with the evolution of CO₂ and CO, probably due to the metal-catalyzed oxidation of acetylacetone by O₂ gas. (118)

Oxygen gas can fully oxidize gold in the presence of 4-pyridinethiol (4-PS) in methanol or ethanol solutions. (119) No dissolution of gold was observed in an argon atmosphere, indicating that oxygen is required as oxidizing agent in this oxidative dissolution process. The dissolution rate increases noticeably with increasing 4-PS concentration, whereas the oxygen pressure had only a marginal effect. Increased temperature (80 °C) only increased the dissolution rate at the very beginning of the reaction. Afterward, the gold concentration in the solution decreased rapidly and finally dropped to zero. This is due to the thermal instability of the soluble gold(I) complex which decomposes to 4,4′-dipyridyl sulfide, elemental sulfur, and metallic gold. Moreover, 4-PS decomposes at room temperature under the reaction conditions and this decomposition is enhanced at elevated temperatures, which can be a reason for the low gold concentration in the solution. Furthermore, Cu(II) ions accelerate the dissolution of gold as well.

Other organic compounds which have similar structure to 4-pyridinethiol cannot dissolve gold in ethanol solutions, for example, pyridine, thiophenol, and 4,4′-pyridyl disulfide (4,4′-PSSP) (Scheme 14). (119) 2-PS can dissolve gold, but with a significantly reduced rate. Therefore, the pyridinethiol structural unit is required for dissolution, and the relative positions of the N and S atoms on the heterocycle affect the efficiency of the dissolution process. The same amount of gold can be quantitatively dissolved by 4-PS within 2 days, while with 2-PS the dissolution takes several weeks to occur. In addition, silver and copper can be dissolved in 4-PS–ethanol solutions, whereas palladium, platinum, and titanium did not react. This selectivity might be related to an oxidation state +1 for group 11 elements.

Scheme 14. Structure of 4-Pyridinethiol (4-PS) That Was Effective for Dissolution of Gold and Other Organic Components with Similar Structures to 4-Pyridinethiol

A dissolution mechanism was proposed by the authors (Figure 11). Dissolution of gold proceeds through several steps: (1) isomerization of 4-pyridinethiol to pyridine-4-thione, (2) coordination with gold(0) from the corners of gold thin films, and (3) 4-pyridinethiol-assisted oxidation of gold(0) by loss of a hydrogen atom from one of the coordinated thiols with oxygen gas as oxidizing agent, and finally, (4) alcohols, although weak Brønsted acids, provide a proton, whereas a negatively charged alkoxide moiety ensures a charge balance. Note that the thermally instable gold(I) complex decomposes and forms 4,4′-dipyridyl sulfide, elemental sulfur, and metallic gold when kept at 80 °C for several hours.

Figure 11. Proposed reaction mechanism for the oxidation of gold with 4-pyrindinethiol (4-PS) in alcohol solutions in open air. Reproduced with permission from ref (119). Copyright 2007 American Chemical Society.

Similar work was conducted by the same research group with dissolution of gold based on the same ligand 4-PS, but with hydrogen peroxide as oxidizing agent dissolved in DMF. (120) Due to the strong oxidizing capability of hydrogen peroxide, the dissolution rate in this new solvent system was 1600 times faster than in the previously reported 4-PS-EtOH-O₂ system. (119) Moreover, the latter system decomposes 4-pyridinethiol to elemental sulfur, whereas hydrogen peroxide can further oxidize elemental sulfur to the sulfate anion (SO₄^2–), which can act as counterion of the gold(I) complex bearing two 4-PS ligands ([Au(4-PS)₂]₂[SO₄]). The other ligands 4-PS, 2-PS, 4,4′-PSSP, and 2-mercaptobenzimidazole (2-MBIH) shown in Scheme 14 with hydrogen peroxide in DMF could dissolve gold and followed the order: 4-PS d(84%) > 2-PSH = 4,4′-PSSP (11%) > 2-MBIH (8%). The dissolution rate is related to the formation energy of the bis-ligand intermediate. The bis-ligand intermediates can lower the oxidation potential of gold significantly because of the delocalization of the 6s¹ electron on the ligands, thus allowing a one-electron oxidation of the ligand instead of the metal. 4-PS with hydrogen peroxide could dissolve copper and silver with high efficiencies, but platinum and palladium did not react, as their dissolution would involve a two-electron oxidation reaction.

Oxidative dissolution of various metals (Cu, Sn, Bi, In, Fe, Sm, Mg, and Ca) was observed using oxygen gas as oxidizing agent in the presence of triflic acid (HOTf) in DMSO, with formation of metallic triflates. (121) Similarly, several metals (Cu, Sn, Bi, and Mg) reacted with triflimidic acid (HNTf₂) in O₂/DMSO to form metallic triflimides. The metallic salts formed were solvated by DMSO. The reaction mechanism is shown in eq 21 using the oxidative dissolution of Bi in HOTf as an example.

(21)

Alternatively, the metal triflates and triflimides salts could be prepared under ultrasonic conditions in the presence of the corresponding protic acid in organic polar solvents. (122)

Organometallic compounds can be synthesized by direct oxidation of metals in organic solvents (= direct synthesis). (123−125) Since direct synthesis is a vast research area, we give in this review only a few representative examples and the reader is referred to the reviews in refs (125−127) for more detailed information. Direct synthesis of nickel complexes was achieved by interaction of nickel metal with ammonium chloride or thiocyanate in the presence of triethylenediamine (Ten) in organic solvents such as DMF, DMSO, MeOH, and ACN. Examples of formed complexes were Ni(HTen)(Ten)Cl₃, Ni(Ten)₂(NH₃)₂(NCS)₂·4DMSO, and Ni(HTen)(NCS)₃·3DMF. (124) The solvents DMF and DMSO were better than MeOH and ACN for dissolution of metals, because insoluble compounds were formed in MeOH and acetonitrile and prevented the completion of dissolution. By reaction of manganese metal and cadmium halide (chloride or iodide) with Schiff base ligand N,N’-ethylene-bis-salicylideneaminato (salen) in nonaqueous solutions of DMF or methanol, mixed-metal complexes were formed, namely [Mn(salen)(dmf)₂]₃[Mn(salen)(dmf)(H₂O)][CdCl₄]₂·H₂O and [Mn(salen)(CH₃OH)]₂[Mn(salen)(CH₃OH)₂]₂[CdI₄]₂. (128) Direct synthesis of polynuclear and mixed-valent metal complexes from elemental metals was reviewed in nonaqueous solutions of the proton-donating reagents ammonium or alkylammonium salts (NH₄X). (125) Oxygen was involved in the reaction as oxidizing agent. Various metal complexes were obtained through this synthetic method, such as the mixed-valent copper complex [Cu(II)(DMSO)₄(H₂O)₂][Cu(I)₄(SCN)₂(CN)₃]₂ and the mixed-metal complex [CuPbBr₂(Me₂Ea)₂DMSO]₂ (Ea is 2-aminoethanol). Examples of the reaction mechanism are presented in eq 22–25), where M, NH₄X, and Ea represent metal, ammonium halides, and 2-aminoethanol, respectively.

(22)

(23)

(24)

(25)

6.2. Nitrogen Dioxide

We mentioned in section 2.1 that uranium can be oxidized by chlorine in the presence of TBP in TCE, but it can also be oxidized by nitrogen dioxide (NO₂) in TBP-TCE at moderate temperatures (30–70 °C). (129) The reaction rate increases with an increase in TBP and NO₂ concentrations. The reaction mechanism is proposed as shown in eq 26, with NO₂ acting as oxidizing agent and TBP as donor solvent.

(26)

The dissolution rate of uranium increased in the presence of water and reached the maximum at a water content of 1.0–2.0 vol %, which is similar to the system of TBP–TCE–Cl₂. (30) The possible reason for this increase is the formation of HNO₃ from the reaction between NO₂ and water. The organic solvent mixture TBP–TCE (30:70 v/v) can be replaced by DMF, DMSO, acetonitrile, nitromethane, diethylformamide, or hexamethylphosphoramide (HMPA). (129) In all systems, uranium metal did react with NO₂ at an appreciable rate, but HMPA reacted vigorously with NO₂, and its nitration rate is considerably higher than the uranium dissolution rate.

6.3. Copper(II) Bromide

Another oxidizing agent that can be used for metal dissolution is copper(II) bromide, CuBr₂. (130,131) Gold can be dissolved oxidatively in DMSO or propylene carbonate (PC) in the presence of CuBr₂, where copper(II) acts as an oxidizing agent and bromide as complexing agent that can significantly lower the reduction potential of gold. (130) Addition of KBr can enhance the total dissolution amount of gold which can be further improved with increasing concentration of CuBr₂ and KBr. When only CuBr₂ is used in DMSO, oxidation of gold(0) to gold(III) is the dominant process, whereas upon addition of KBr, oxidation of gold(0) to gold(I) takes place as well. The reaction mechanisms are shown in eqs 27 and 28:

(27)

(28)

The metals Pd, Cu, Sn, Co, Ni, and Zn can be dissolved at a relatively fast rate in CuBr₂–PC, while Ag, Ta, Ti, and W cannot, probably due to the presence of a passivating oxide film on the metal surface of Ag, Ta, Ti, and W.

6.4. Organic Compounds

Supercritical carbon dioxide (scCO₂) has been investigated as leaching agent for etching of metal layers such as copper and zinc on silicon substrates in the microelectronic industry, to avoid the technical and environmental drawbacks of aqueous-based processes and organic solvents-based processes. (132−135) Copper was etched by a homogeneous solution in scCO₂ that contained an oxidizing agent and a β-diketone chelating agent with formation of copper(II) complexes. The oxidizing agents were ethyl peroxydicarbonate (EPDC) and tert-butyl peracetate (t-BuPA). Various chelating agents were investigated, namely1,1,1-trifluoro-2,4-pentanedione (Htfac), hexafluoroacetylacetone (Hhfac), 2,2,6,6-tetramethyl-3,5-heptanedione (Htmhd), substituted bis(acetylacetonate)ethylenediimine (R₄BAE, where R = CH₃ or CF₃), and lithium or sodium dialkyldithiocarbamate (M⁺(R₂DTC^–), where M⁺ = Li⁺ or Na⁺ and R = ethyl, n-propyl, n-butyl, or 1,1,1-trifluoroethyl) ligands. The structures of the oxidizing agents and the chelating agents are shown in Scheme 15.

Scheme 15. Chemical Structures of Oxidizing Agents and Chelating Agents for Dissolution of Copper in Supercritical CO₂

The efficiencies of copper removal by the mixtures of various oxidizing agents and chelating agents in scCO₂ are listed in Table 5. It is noteworthy to mention that the solution of t-BuPA should be treated as potentially explosive and should be handled with care. Moreover, the leaching efficiency of different leaching solutions presented in different references cannot be compared, because the dimensions of the copper metal samples and the experimental conditions were different. The efficiency of copper removal using EPDC as oxidizing agent followed the order: Htmhd ≈ Htfac < Hhfac. This trend is in agreement with the solubility of the formed product in scCO₂. By dissolution of metals, tert-butyl peracetate was decomposed to tert-butyl alcohol and acetic acid. (133) The oxidative dissolution rate of copper was increased as the alkyl chain length in R₂DTC^– increased or as fluorine substitution was introduced for both the R₄BAE and R₂DTC^– ligands. The Li(R₂DTC) salts were more effective in copper removal than Na(R₂DTC). The kinetics of oxidation and removal of copper were independent of the concentration of oxidizing agents but varied with the concentration of chelating agents. (135)

Table 5. Efficiency of copper Removal in scCO₂ in the Presence of Oxidizing Agents and Chelating Agents

Oxidizing agent	Chelating agent	Cu removal (%)	Conditions	Reference
EPDC	Hhfac	34	40 °C and 214 bar for 20 h	(132)
EPDC	Htfac	12	40 °C and 214 bar for 20 h	(132)
EPDC	Htmhd	11	40 °C and 214 bar for 20 h	(132)
t-BuPA	Hhfac	14	40 °C and 214 bar for 20 h	(133)
t-BuPA	Htfac	1	40 °C and 214 bar for 20 h	(133)
t-BuPA	Htmhd	4	40 °C and 214 bar for 20 h	(133)
t-BuPA	Me₄BAE	28	40 °C and 207 bar for 18 h	(134)
t-BuPA	Me₂(CF₃)₂BAE	22	40 °C and 207 bar for 18 h	(134)
t-BuPA	(CF₃)₄BAE	44	40 °C and 207 bar for 18 h	(134)
t-BuPA	Li(Et₂DTC)	24	40 °C and 172 bar for 4 h	(134)
t-BuPA	Li(Pr₂DTC)	27	40 °C and 172 bar for 4 h	(134)
t-BuPA	Li(Bu₂DTC)	28	40 °C and 172 bar for 4 h	(134)
t-BuPA	Li(CF₃CH₂)₂DTC)	36	40 °C and 172 bar for 4 h	(134)
t-BuPA	Na(Et₂DTC)	20	40 °C and 172 bar for 4 h	(134)
t-BuPA	Na(Pr₂DTC)	20	40 °C and 172 bar for 4 h	(134)
t-BuPA	Na(Bu₂DTC)	23	40 °C and 172 bar for 4 h	(134)

It was found that Hhfac in scCO₂ without added oxidizing agent can also etch metal films (e.g., Fe, Cu, Ni, and Co) at relatively high temperature (100–250 °C) at 100 bar. (136) The reaction mechanism might consist of two steps (eqs 29 and 30), regardless of the stoichiometry:

(29)

(30)

Without any oxidizing agent, the etching could be initiated by the reaction between Hhfac and a native metal oxide layer on the metal surface, with formation of M(hfac)₂ and water. Water then acted as an oxide source to react with metal to make the etching reaction proceed further.

Electrochemical synthesis of metallic bis(trifluoromethanesulfonyl)imide salts (NTf₂^–) was reported using a sacrificial metal anode and the acid bis(trifluoromethanesulfonyl)imide as electrolyte in a polar organic solvent such as DMF or nitromethane at room temperature. (137) The metal was oxidized at the anode, and the acid HNTf₂ was reduced at the cathode to form the NTf₂^– anion and hydrogen gas. Electrochemical dissolution of a sacrificial metal anode in nonaqueous solvents could also direct synthesis of the organometallic compound. (127) Silver was electrochemically dissolved in benzene with crown-ether-complexed sodium tetraphenylborate as electrolyte. However, copper and zinc could not be oxidized under same conditions. (138) Furthermore, ultrasonic treatment could increase the oxidative dissolution rate of copper in nonaqueous solutions, because the product layer was removed from the metal surface to enhance the further dissolution of metals. (139)

7. Conclusions and Outlook

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Dissolution of metals in organic solvents has been studied for more than half a century. Various leaching systems containing different oxidizing agents have been developed for dissolution of metals and for application in various fields, such as extraction of metals from ores, chemical etching of semiconductors, separation of metals and metal oxides, and metal recovery from end-of-life products. Some leaching systems such as halogens in organic solvents were studied for dissolution of various metals including both base metals and noble metals. Other leaching systems were studied with a focus on certain types of metals. For example, the dihalogen or interhalogen adducts were used most often for dissolution of noble metals. Although these leaching systems can oxidize metals, the volatility of halogens and organic solvents makes processes involving these leaching systems less attractive. Moreover, some of these leaching systems are toxic, such as SO₂ and SOCl₂. Polyhalide ILs have attracted interest for dissolution of metals due to their unique properties. On one hand, they are strongly oxidizing agents, and on the other hand, they can safely store halogens, which make them easily to handle. Solvent systems containing ILs and DESs have several advantages compared to those that are based on molecular organic solvents: they have low volatility and a wide liquid range. They can be used as electrolytes in electrochemical processes for dissolution of metals such as electropolishing, because of their ionic characteristics. Moreover, the reduction potential of metals can be lowered in ILs and DESs, which makes the oxidation of these metals easier. However, the prices of DES and especially of ILs are usually much higher than those of conventional organic solvents. To design an economically feasible process, the dissolution efficiency needs to be improved and meanwhile the recycling of solvents is a must. This review gives an overview of the state of the art of technologies for dissolution of metals, and it is hoped that it might inspire other researcher to carry out further work in this field.

Author Information

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Corresponding Author
- Koen Binnemans - KU Leuven, Department of Chemistry, Celestijnenlaan 200F, P.O. Box 2404, B-3001 Leuven, Belgium; http://orcid.org/0000-0003-4768-3606; Email: [email protected]
Author
- Xiaohua Li - KU Leuven, Department of Chemistry, Celestijnenlaan 200F, P.O. Box 2404, B-3001 Leuven, Belgium; http://orcid.org/0000-0003-4555-8705
Notes
The authors declare no competing financial interest.

Biographies

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Xiaohua Li

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Xiaohua Li was born in Anyang, China. She obtained her master degree from Chinese Academy of Sciences, Institute of Process Engineering under the supervision of Prof. Suojiang Zhang and obtained her doctor degree under the supervision of Prof. Sascha R.A. Kersten and Prof. Boelo Schuur from University of Twente in The Netherlands in February 2017. From November 2016 to the present, she has worked as a postdoc researcher with Prof. Koen Binnemans at KU Leuven in Belgium. In October 2019, she received an individual postdoc fellowship from the Research Foundation Flanders (FWO) and continued to work in the same group. Her main research interests are ionic liquids, oxidative dissolution of metals in nonaqueous solutions, metal recovery, solvent extraction, separation technology, and aqueous biphasic systems.

Koen Binnemans

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Koen Binnemans was born in Geel, Belgium. He obtained his M.Sc. (1992) and Ph.D. (1996) degrees in Chemistry at the University of Leuven (KU Leuven). In the period 1999–2005, he was a postdoctoral fellow of the Research Foundation Flanders. From 2005 until 2010 he was a professor, and presently he is full professor of Chemistry at the University of Leuven. He has published over 500 papers in international scientific journals. His main research interests are metallurgical chemistry, solvometallurgy, solvent extraction, and ionic liquids. As an ERC Advanced Grant holder (SOLCRIMET), he is cofounder of the SOLVOMET Industrial Service Centre for Solvometallurgy. He is an elected member of the Royal Flemish Academy of Belgium for Science and the Arts (KVAB).

Acknowledgments

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The research leading to these results received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Programme: Grant Agreement 694078—Solvometallurgy for critical metals (SOLCRIMET). The research was also funded by a postdoctoral grant of the Research Foundation Flanders (FWO) to X. Li (12ZA520N).

Abbreviations

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(PhHN)₂DTM	N,N’-diphenyl dithiomalonamide
(PhHN)₂DTL	3,5-bis(phenylamino)-1,2-dithiolylium
2-MBIH	2-mercaptobenzimidazole
2-MBPy	1-butyl-2-methylpyridinium
4-MBPy	1-butyl-4-methylpyridinium
4-PS	4-pyridinethiol
4,4′-PSSP	4,4′-pyridyl disulfide
ACN	acetonitrile
Bmim	1-butyl-3-methylimidazolium
BMPip	1-butyl-1-methylpiperidinium
BMPyrr	1-butyl-1-methylpyrrolidinium
BPy	1-butylpyridinium
BuOAc	butyl acetate
CAN	acetonitrile
CPB	cetylpyridinium bromide
CPI	cetylpyridinium iodide
DESs	deep eutectic solvents
DMAA	dimethylacetamide
DMF	N,N-dimethylformamide
Dmim	1-decyl-3-methylimidazolium
DMSO	dimethyl sulfoxide
Ea	2-aminoethanol
EG	ethylene glycol
EPDC	peroxydicarbonate
Et₄TDS	tetraethylthiuram disulfide
EtOAc	ethyl acetate
EtOH	ethanol
GEOBROM 3114	1-chloro-3-bromo-5,5-dimethylhydrantoin
GEOBROM 5500	1,3-dibromo-5,5-dimethylhydantoin
Hhfac	hexafluoroacetylacetone
HMPA	hexamethylphosphoramide
HNTF₂	triflimidic acid
HOTf	triflic acid
HPy	1-hexylpyridinium
Htfac	1,1,1-trifluoro-2,4-pentanedione
Htmhd	2,2,6,6-tetramethyl-3,5-heptanedione
HX	halide acid
ILs	ionic liquids
mbit	1-methyl-1H-benzimidazole-2(3H)-thione
mbtt	3-methyl-benzothiazole-2-thione
Me₂dazdt	N,N’-dimethylperhydrodiazepine-2,3-dithione
Me₂Pipdt	N,N’-dimethylpiperazinium-2,3-dithione
MeOAc	methyl acetate
MeOH	methanol
Mo₂DTL	3,5-bis(morpholino)-1,2-dithiolylium
Mo₂DTM	dimorpholyldithiomalonamide
N₁₈₈₈	Methyltrioctylammonium
N₄₄₄₄	tetrabutylammonium
NBS	N-bromosuccinimide
Nd–Fe–B	neodymium–iron–boron
NH₄X	ammonium halides
NTf₂^–	bis(trifluoromethane)sulfonamide
P₄₄₄₁₀	tributyldecylphosphonium
P_444,14	tributyl(tetradecyl)phosphonium
P₄₄₄₄	tetrabutylphosphonium
P_666,14	trihexyl(tetradecyl)phosphonium
PGMs	platinum-group metals
Py	pyridine
R₂DTC	dialkyldithiocarbamate
REEs	rare-earth elements
salen	N,N’-ethylene-bis-salicylideneaminato
scCO₂	supercritical carbon dioxide
SEM	scanning electron microscopy
Sm–Co	samarioum-cobalt
t-BuPA	tert-butyl peracetate
TBP	tri-n-butylphosphate
TCE	tetrachloroethylene
Ten	triethylenediamine

References

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This article references 139 other publications.

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Rodriguez Rodriguez, Nerea; Machiels, Lieven; Onghena, Bieke; Spooren, Jeroen; Binnemans, Koen
RSC Advances (2020), 10 (12), 7328-7335CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
A review. Several deep-eutectic solvents (DESs) were tested for the valorisation of goethite residue produced by the zinc industry. The objective of the work was to selectively recover zinc from the iron-rich matrix using deep-eutectic solvents as lixiviants. The effect of the type of hydrogen bond donor and hydrogen bond acceptor of the deep-eutectic solvent on the leaching efficiency was studied. Levulinic acid-choline chloride (xChCl = 0.33) (LevA-ChCl) could selectively leach zinc from the iron-rich matrix, and it was selected as the best-performing system to be used in further study. The leaching process was optimized in terms of temp., contact time, liq.-to-solid ratio and water content of the deep-eutectic solvent. The role of the choline cation on the leaching process was investigated by considering the leaching properties of a LevA-CaCl2 mixt. The goethite residue was also leached with pure levulinic acid. The results were compared to a purely hydrometallurgical approach using sulfuric acid leaching. Leaching with LevA-ChCl resulted in higher selectivity compared to the conventional "hot leaching" with 80 g L-1 sulfuric acid. Furthermore, a slightly higher zinc recovery and comparable selectivity for zinc over iron were achieved with LevA-ChCl compared to conventional "neutral leaching" with 10 g L-1 sulfuric acid.
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European Commission. Communication from the Commission to the European Parliament, the Council, the Eurpean Economic and Social Committee and the Committee of the Regions on the 2017 List of Critical Raw Materials for the EU. 2017.
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Ellis, L. US Department of the Interior - Office of the Secretary: Final List of Critical Minerals 2018. Fed. Regist. 2018, 83, 23295– 23296
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Sheng, P. P.; Etsell, T. H. Recovery of Gold from Computer Circuit Board Scrap Using Aqua Regia. Waste Manage. Res. 2007, 25, 380– 383, DOI: 10.1177/0734242X07076946
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Recovery of gold from computer circuit board scrap using aqua regia
Sheng, Peter P.; Etsell, Thomas H.
Waste Management & Research (2007), 25 (4), 380-383CODEN: WMARD8 ISSN:. (Sage Publications Ltd.)
Computer circuit board scrap was first treated with one part concd. nitric acid and two parts water at 70° for 1 h. This step dissolved the base metals and thereby liberated the chips from the boards. After solid-liq. sepn., the chips, intermixed with some metal flakes and tin oxide ppt., were mech. crushed to liberate the base and precious metals contained within the protective plastic or ceramic chip cases. The base metals in the crushed product were dissolved by leaching again with the same type of nitric acid-water soln. The remaining solid constituents, crushed chips and resin, plus solid particles of gold, were leached with aqua regia at various times and temps. Gold was pptd. from the leachate with ferrous sulfate.
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Gökelma, M.; Birich, A.; Stopic, S.; Friedrich, B. A Review on Alternative Gold Recovery Re-Agents to Cyanide. J. Mater. Sci. Chem. Eng. 2016, 04, 8– 17, DOI: 10.4236/msce.2016.48002
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Binnemans, K.; Jones, P. T. Solvometallurgy: An Emerging Branch of Extractive Metallurgy. J. Sustain. Metall. 2017, 3, 570– 600, DOI: 10.1007/s40831-017-0128-2
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Li, X.; Monnens, W.; Li, Z.; Fransaer, J.; Binnemans, K. Solvometallurgical Process for Extraction of Copper from Chalcopyrite and Other Sulfidic Ore Minerals. Green Chem. 2020, 22, 417– 426, DOI: 10.1039/C9GC02983D
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Solvometallurgical process for extraction of copper from chalcopyrite and other sulfidic ore minerals
Li, Xiaohua; Monnens, Wouter; Li, Zheng; Fransaer, Jan; Binnemans, Koen
Green Chemistry (2020), 22 (2), 417-426CODEN: GRCHFJ; ISSN:1463-9262. (Royal Society of Chemistry)
Extn. of copper from sufidic ores, either by pyrometallurgy or hydrometallurgy, has various limitations. In this study, a solvometallurgical process for the extn. of copper from sulfidic ore minerals (chalcopyrite, bornite, chalcocite and digenite) was developed by using an org. lixiviant (FeCl3 as oxidizing agent and ethylene glycol (EG) as org. solvent). All the studied copper sulfide minerals could be leached efficiently with a FeCl3-EG soln. Other lixiviant systems, namely CuCl2-EG, FeCl3-ethanol and FeCl3-propylene glycol could also ext. copper, but they did not perform as well as the FeCl3-EG solns. The mechanistic study of chalcopyrite leaching in FeCl3-EG solns. confirmed that the leaching products of chalcopyrite were FeCl2, CuCl and solid elemental sulfur, where the Fe(II) and Cu(I) were quantified by UV-Vis absorption spectroscopy and solid sulfur was identified by powder x-ray diffraction. A kinetic study showed that the leaching process was a surface chem. controlled process and the apparent activation energy was calcd. to be 60.1 kJ mol-1. Subsequently, electrodeposition of copper from the pregnant leachate was investigated, and SEM-energy-dispersive x-ray anal. showed that uniform cubic cryst. deposits of pure copper were produced. Meanwhile, the Fe(III) was regenerated by oxidizing Fe(II) at the anode, with a Morgane membrane in between two electrode compartments to prevent the transfer of Fe(III) to the cathode. Finally, a closed-loop solvometallurgical process was designed with three operational steps: leaching, electrodeposition and removal of Fe(II). The regeneration of the FeCl3-EG soln. and the use of EG contribute to the sustainability and the greenness of the process.
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Li, Z.; Zhang, Z.; Smolders, S.; Li, X.; Raiguel, S.; Nies, E.; De Vos, D. E.; Binnemans, K. Enhancing Metal Separations by Liquid–Liquid Extraction Using Polar Solvents. Chem. - Eur. J. 2019, 25, 9197– 9201, DOI: 10.1002/chem.201901800
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Enhancing Metal Separations by Liquid-Liquid Extraction Using Polar Solvents
Li, Zheng; Zhang, Zidan; Smolders, Simon; Li, Xiaohua; Raiguel, Stijn; Nies, Erik; De Vos, Dirk E.; Binnemans, Koen
Chemistry - A European Journal (2019), 25 (39), 9197-9201CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
The less polar phase of liq.-liq. extn. systems was studied extensively for improving metal sepns.; however, the role of the more polar phase was overlooked for far too long. Herein, we investigate the extn. of metals from a variety of polar solvents and demonstrate that, the influence of polar solvents on metal extn. is so significant that extn. of many metals can be largely tuned, and the metal sepns. can be significantly enhanced by selecting suitable polar solvents. Furthermore, a mechanism on how the polar solvents affect metal extn. is proposed based on comprehensive characterizations. The method of using suitable polar solvents in liq.-liq. extn. paves a new and versatile way to enhance metal sepns.
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Li, Z.; Mercken, J.; Li, X.; Riaño, S.; Binnemans, K. Efficient and Sustainable Removal of Magnesium from Brines for Lithium/Magnesium Separation Using Binary Extractants. ACS Sustainable Chem. Eng. 2019, 7, 19225– 19234, DOI: 10.1021/acssuschemeng.9b05436
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Efficient and Sustainable Removal of Magnesium from Brines for Lithium/Magnesium Separation Using Binary Extractants
Li, Zheng; Mercken, Jonas; Li, Xiaohua; Riano, Sofia; Binnemans, Koen
ACS Sustainable Chemistry & Engineering (2019), 7 (23), 19225-19234CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
Lithium is becoming increasingly important due to its essential role in lithium-ion batteries. Over 70% of the global lithium resources are found in salt lake brines, but lithium is always accompanied by magnesium. It is a challenge to efficiently sep. lithium from magnesium in brines. The state-of-the-art processes for lithium/magnesium sepn. either consume large quantities of chems. and generate large amts. of waste or are energy-intensive. In this study, we develop a sustainable solvent extn. process based on binary extractants to efficiently sep. lithium and magnesium. A binary extractant composed of Aliquat 336 and Versatic Acid 10, [A336][V10], was prepd. and investigated for removal of magnesium from both a (synthetic) concd. brine (106 g L-1 Mg and 10 g L-1 Li) and an (synthetic) original brine (15 g L-1 Mg, 80 g L-1 Na and 0.2 g L-1 Li). Through batch counter-current expts. and mixer-settler expts., it was found that [A336][V10] is able to quant. remove magnesium from the original brine in three continuous counter-current extn. stages with as little as about 10% coextn. of lithium. The loaded org. phase can be stripped and regenerated by water. The whole process (extn. and stripping) does not consume any acid or base but makes use of the differences in the chloride concn. during extn. and stripping. This process is an environmentally friendly alternative to the state-of-the-art processes and represents a step forward in the sustainable prodn. of Li2CO3 from brines. The binary extractant [A336][V10] removes magnesium from brine solns. selectively and efficiently without consumption of any acid or base.
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Li, X.; Li, Z.; Orefice, M.; Binnemans, K. Metal Recovery from Spent Samarium-Cobalt Magnets Using a Trichloride Ionic Liquid. ACS Sustainable Chem. Eng. 2019, 7, 2578– 2584, DOI: 10.1021/acssuschemeng.8b05604
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Metal Recovery from Spent Samarium-Cobalt Magnets Using a Trichloride Ionic Liquid
Li, Xiaohua; Li, Zheng; Orefice, Martina; Binnemans, Koen
ACS Sustainable Chemistry & Engineering (2019), 7 (2), 2578-2584CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
Recycling of samarium-cobalt (SmCo) magnets is essential due to the limited resources of the mentioned metals and their high economic importance. The ionic liq. (IL) trihexyltetradecylphosphonium trichloride, [P666,14][Cl3], which can safely store Cl gas in the form of the trichloride anion, was used as an oxidizing solvent for the recovery of metals from spent SmCo magnets. The dissoln. was studied considering various mixts. of the ILs [P666,14][Cl3] and [P666,14]Cl, solid-to-liq. ratios and different temps. The results showed that the max. capacity of [P666,14][Cl3] for SmCo magnets was 71±1 mg/g of [P666,14][Cl3], in the presence of an extra source of coordinating Cl-. The max. loading of the IL could be reached within 3 h at 50°. Four stripping steps effectively removed all metals from the loaded IL, where NaCl soln. (3 mol/L), twice water and ammonia soln. (3 mol/L) were used consecutively as the stripping solvents. The regenerated IL showed a similar dissoln. performance as fresh IL. Oxidative dissoln. of metals in trichloride ILs is easily transferable to the recycling of valuable metals from other end-of-life products such as Nd-Fi-B magnets and Ni metal hydride batteries.
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Deferm, C.; Malaquias, J. C.; Onghena, B.; Banerjee, D.; Luyten, J.; Oosterhof, H.; Fransaer, J.; Binnemans, K. Electrodeposition of Indium from the Ionic Liquid Trihexyl(Tetradecyl)Phosphonium Chloride. Green Chem. 2019, 21, 1517– 1530, DOI: 10.1039/C8GC03389G
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Electrodeposition of indium from the ionic liquid trihexyl(tetradecyl)phosphonium chloride
Deferm, Clio; Malaquias, Joao C.; Onghena, Bieke; Banerjee, Dipanjan; Luyten, Jan; Oosterhof, Harald; Fransaer, Jan; Binnemans, Koen
Green Chemistry (2019), 21 (6), 1517-1530CODEN: GRCHFJ; ISSN:1463-9262. (Royal Society of Chemistry)
The electrochem. behavior of In in the ionic liq. trihexyl(tetradecyl)phosphonium chloride (Cyphos IL 101) was studied. Cyphos IL 101 1st had to be purified, as the impurities present in com. Cyphos IL 101 interfered with the electrochem. measurements. Electrochem. deposition of In metal from this electrolyte occurs without H evolution, increasing the cathodic current efficiency compared to deposition from H2O and avoiding porosity within the deposited metal. Indium(III) is the most stable oxidn. state in the ionic liq. This ion is reduced in two steps, 1st from In(III) to In(I) and subsequently to In(0). The high thermal stability of Cyphos IL 101 allowed the electrodeposition of In at 120° and 180°. At 180° In was deposited as liq. In which allows for the easy sepn. of the In and the possibility to design a continuous electrowinning process. On Mo, In deposits as liq. droplets even below the m.p. of In. This was explained by the combination of m.p. depression and undercooling. The possibility to sep. In from Fe and Zn by electrodeposition was tested. It is possible to sep. In from Zn by electrodeposition, but Fe deposits together with In.
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Abbott, A. P.; Frisch, G.; Gurman, S. J.; Hillman, A. R.; Hartley, J.; Holyoak, F.; Ryder, K. S. Ionometallurgy: Designer Redox Properties for Metal Processing. Chem. Commun. 2011, 47, 10031– 10033, DOI: 10.1039/c1cc13616j
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Ionometallurgy: designer redox properties for metal processing
Abbott, A. P.; Frisch, G.; Gurman, S. J.; Hillman, A. R.; Hartley, J.; Holyoak, F.; Ryder, K. S.
Chemical Communications (Cambridge, United Kingdom) (2011), 47 (36), 10031-10033CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
The first electrochem. series in a deep eutectic solvent is described. Speciation resulting from the unusual chem. of the choline chloride based deep eutectic solvent is used to explain both similarities and differences from aq. media. Examples are given of how these differences can be exploited in technol. important systems as a solvent in hydrometallurgical systems.
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Larsen, R. P. Dissolution of Uranium Metal and Its Alloys. Anal. Chem. 1959, 31, 545– 549, DOI: 10.1021/ac50164a026
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Solution of uranium metal and its alloys
Larsen, Robert P.
(1959), 31 (), 545-9CODEN: ANCHAM; ISSN:0003-2700.
The most useful methods for the soln. of U metal and its alloys are reviewed, with particular emphasis on the prepn. of solns. for analysis. The behavior of the metal and its alloys in the common acids, EtOAc solns. of Br and HCl, and NaOH-H2O2 mixts. is described. Recommendations for dissolving each of a wide variety of U alloys are summarized in tabular form. 10 references.
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Eberle, A. R.; Lerner, M. W. Determination of Boron in Beryllium, Zirconium, Thorium, and Uranium Dissolution in Bromine-Methanol. Anal. Chem. 1960, 32, 146– 149, DOI: 10.1021/ac60158a001
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Determination of boron in beryllium, zirconium, thorium, and uranium. Dissolution in bromine-methanol
Eberle, A. R.; Lerner, M. W.
(1960), 32 (), 146-9CODEN: ANCHAM; ISSN:0003-2700.
B (0.10-500 p.p.m.) in Be, Zr, Th, and U can be detd. by dissoln. of the metal in Br-MeOH followed by distn. of the boron ester and color development with diaminochrysazin (cf. Cogbill and Yoe, C.A. 51, 17571e). In the case of Zr, Th, and U, more Br than that required for stoichiometry is added to enable a reasonably fast reaction, the excess Br being consumed by Be scavenger. More than recommended quantities of Be scavenger tend to give low results. The recovery of B is complete even by distg. 50% of the anhyd. reaction mixt. only, thus saving time and minimizing the quantities in the distillate of Br and bromide which in large amts. may interfere. The fluoride ion in the sample is not distd. The distillate is treated with lime suspension to hydrolyze the Me borate and to prevent hydrolysis of the resulting salt to the volatile free acid. On evapn. H2SO4 is added to the residue prior to absorbance measurements. The precision and accuracy of the method are good. The analysis of 2 samples of Zircaloy (15 detns.) showed an av. deviation of ±0.00058 and ±0.00107, resp.
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Beeghly, H. F. Determination of Aluminum Nitride Nitrogen in Steel. Anal. Chem. 1949, 21, 1513– 1519, DOI: 10.1021/ac60036a024
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Determination of aluminum nitride nitrogen in steel
Beeghly, H. F.
(1949), 21 (), 1513-19CODEN: ANCHAM; ISSN:0003-2700.
If a sample of steel is extd. with Br and MeOAc under a reflux condensor, all the Fe is dissolved and the residue contains AlN. The N can be detd. by the procedure described in (C.A. 36, 1866.9). A suitable app. is shown; 32 references.
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Busheina, I. S.; Headridge, J. B. Studies in Chemical Phase Analysis Part I. Determination of the Solubilities of Elements in Certain Organic Solvent - Bromine Mixtures. Analyst 1980, 105, 600– 604, DOI: 10.1039/an9800500600
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Studies in chemical phase analysis. Part 1. Determination of the solubilities of elements in certain organic solvent-bromine mixtures
Busheina, I. S.; Headridge, J. B.
Analyst (Cambridge, United Kingdom) (1980), 105 (1251), 600-4CODEN: ANALAO; ISSN:0003-2654.
The solubilities of Al, Cr, Co, Cu, Fe, Pb, Mn, Mo, Ni, Nb, P, Si, S, Sn, Ti, W, and V were detd. at 25° in org. solvent-Br mixts. (10:1) after refluxing. MeOAc, BuOAc, and MeCN were used as solvents. Pb, Mo, Si, and W were not appreciably sol. in these solvents. E.g., the soly. of Al was 3.1, 2.8, and 3.4 g/100 mL in MeOAc-Br, BuOAc-Br, and MeCN-Br solns., resp., compared with <0.02, <0.01, and <0.02 g/100 mL, resp., for W.
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Abou Zeid, G. T.; Headridge, J. B. Studies in Chemical Phase Analysis Part III.*Determination of the Solubilities of Certain Elements and Compounds Pertinent to Steels in Organic Solvent - Halogen Mixtures with Particular Emphasis on Manganese Silicon Nitride. Analyst 1982, 107, 200– 205, DOI: 10.1039/an9820700200
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Studies in chemical phase analysis. Part III. Determination of the solubilities of certain elements and compounds pertinent to steels in organic solvent-halogen mixtures with particular emphasis on manganese silicon nitride
Abou Zeid, G. T.; Headridge, J. B.
Analyst (Cambridge, United Kingdom) (1982), 107 (1271), 200-5CODEN: ANALAO; ISSN:0003-2654.
To assist in the development of methods for the detn. of MnSiN2 in steels contg. Al or Nb nitrides, the solubilities of Fe and MnSiN2 were detd. in MeOH and Me acetate each contg. a halogen or an interhalogen compd. The best solvent for the detn. of Al nitride or Nb nitride in the presence of MnSiN2 is ICl3-Me acetate under reflux. However, for the isolation of MnSiN2 together with the more stable nitrides, I2-Me acetate is the best solvent. The solubilities of Fe and certain other elements and of some compds. of Fe and Mn were detd. in I2-MeOH soln. The solvent is recommended for the isolation of Fe(II) and Mn(II) oxides from steels but Fe(II) and Mn(II) sulfides and cementite are appreciably attacked by the solvent.
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Busheina, I. S.; Headridge, J. B. Studies in Chemical Phase Analysis Part II. Determination of the Solubilities of Carbides, Nitrides, Oxides and Sulphides in Certain Organic Solvent - Bromine Mixtures. Analyst 1981, 106, 221– 226, DOI: 10.1039/an9810600221
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Studies in chemical phase analysis. Part II. Determination of the solubilities of carbides, nitrides, oxides, and sulfides in certain organic solvent-bromine mixtures
Busheina, I. S.; Headridge, J. B.
Analyst (Cambridge, United Kingdom) (1981), 106 (1259), 221-6CODEN: ANALAO; ISSN:0003-2654.
The solubilities of 5 carbides, 7 nitrides, 16 oxides, and 11 sulfides were detd. at 25° in MeOAc- and MeCN-Br mixts. (10:1) after shaking at room temp. and refluxing. AlN, Cr2N, NbN, TiN, and VN had very low solubilities, esp. in MeOAc-Br at room temp. Fe3C and Fe and Mn nitrides were extensively decompd. with the Fe and Mn passing into soln. The oxides were sparingly sol. but the sulfides were appreciably sol.
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Strubbe, K.; Gomes, W. P. Bromine-Methanol as an Etchant for Semiconductors: A Fundamental Study on GaP: I. Etching Behavior of N- and P-Type. J. Electrochem. Soc. 1993, 140, 3294– 3300, DOI: 10.1149/1.2221026
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Bromine-methanol as an etchant for semiconductors: a fundamental study on gallium phosphide. I. Etching behavior of n- and p-type GaP
Strubbe, K.; Gomes, W. P.
Journal of the Electrochemical Society (1993), 140 (11), 3294-300CODEN: JESOAN; ISSN:0013-4651.
Electrochem. and etching expts. were performed at n- and p-type GaP single crystals in the commonly used etchant bromine-methanol to study the fundamental aspects of the etching reaction. The etching properties of these methanolic bromine solns. were similar to those of bromine solns. in which water is used as the solvent; thus, e.g., as in water, the etching kinetics and morphologies at the (111) and (111) faces are markedly different. In many cases of practical etching, methanol may be substituted by water as the solvent for bromine. The results allow one to propose an overall reaction equation for the etch process as well as a detailed mechanism involving radical decompn. intermediates of the semiconductor. These intermediates may further react chem. either with species formed in the etch process itself or with ligands from the soln.
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Sullivan, M. V.; Kolb, G. A. The Chemical Polishing of Gallium Arsenide in Bromine-Methanol. J. Electrochem. Soc. 1963, 110, 585, DOI: 10.1149/1.2425820
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Chemical polishing of gallium arsenide in bromine-methanol
Sullivan, M. V.; Kolb, G. A.
Journal of the Electrochemical Society (1963), 110 (), 585-7CODEN: JESOAN; ISSN:0013-4651.
Best chem. polishing of GaAs is obtained by combining the etchant MeOH contg. a few percent Br with intensive stirring. Etch rates are shown for different crystal faces of GaAs as a function of the Br concn. and the pressure exerted on the crystal. The {111} face of GaAs is the most difficult to polish, but a high polish can be obtained on it by reducing the Br content to 0.0025%.
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Drobot, N. F.; Noskova, O. A.; Ovchinnikova, N. A.; Zvereva, G. A.; Larin, G. M.; Krenev, V. A.; Trifonova, E. N.; Drobot, D. V. Complex Formation during Molybdenum Chlorination in DMF Medium. Russ. J. Coord. Chem. 2003, 29, 474– 477, DOI: 10.1023/A:1024774829021
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Complex Formation During Molybdenum Chlorination in DMF Medium
Drobot, N. F.; Noskova, O. A.; Ovchinnikova, N. A.; Zvereva, G. A.; Larin, G. M.; Krenev, V. A.; Trifonova, E. N.; Drobot, D. V.
Russian Journal of Coordination Chemistry (Translation of Koordinatsionnaya Khimiya) (2003), 29 (7), 474-477CODEN: RJCCEY; ISSN:1070-3284. (MAIK Nauka/Interperiodica Publishing)
IR and EPR studies of solns. formed after Mo chlorination in the medium of DMF revealed the diamagnetic Mo(VI) and paramagnetic Mo(V) complexes R2[MoOCl5], where R is [Me2NCOH2]+ (I) and [Me2NH2]+ (II). The hydrolysis of complex II gave Me2NH2Cl.
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Drobot, N. F.; Trifonova, E. N.; Krenev, V. A.; Drobot, D. V. Oxidative Dissolution of Refractory Metals by Chlorination in Aqueous Organic Media. Russ. J. Coord. Chem. 2005, 31, 243– 246, DOI: 10.1007/s11173-005-0084-4
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Oxidative dissolution of refractory metals by chlorination in aqueous organic media
Drobot, N. F.; Trifonova, E. N.; Krenev, V. A.; Drobot, D. V.
Russian Journal of Coordination Chemistry (2005), 31 (4), 243-246CODEN: RJCCEY; ISSN:1070-3284. (Pleiades Publishing, Inc.)
Chlorination of rhenium, tungsten, and molybdenum with gaseous chlorine in a DMF-water medium was studied. The degree to which the metals pass to the soln. is higher in the presence of water. The activating effect of water is attributed to the catalytic properties of solns. of HCl in DMF. The activating effect on metal dissoln. increases in the sequence W < Mo < Re.
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Drobot, N. F.; Kupriyanova, T. A.; Krenev, V. A.; Filippov, M. N. Rhenium and Platinum Recovery from Platinum and Rhenium Catalysts Used. Theor. Found. Chem. Eng. 2009, 43, 539– 543, DOI: 10.1134/S0040579509040319
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Rhenium and platinum recovery from platinum and rhenium catalysts used
Drobot, N. F.; Kupriyanova, T. A.; Krenev, V. A.; Filippov, M. N.
Theoretical Foundations of Chemical Engineering (2009), 43 (4), 539-543CODEN: TFCEAU; ISSN:0040-5795. (Pleiades Publishing, Ltd.)
The recovery of Re and Pt from spent Pt-Re catalysts is done by chlorinating with chlorine gas mixed with DMF and hydrochloric acid. The two-stage process conducted with a burning residue after the first phase chlorination results in addnl. platinum transfer into the soln. and makes it possible to obtain 70-94% platinum recovery and 91-96% rhenium recovery.
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Chekmarev, A. M.; Buchikhin, E. P.; Sidorov, D. S.; Koshcheev, A. M. Zirconium Dissolution by Low-Temperature Chlorination in Dimethylformamide. Theor. Found. Chem. Eng. 2007, 41, 752– 754, DOI: 10.1134/S0040579507050521
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Zirconium dissolution by low-temperature chlorination in dimethylformamide
Chekmarev, A. M.; Buchikhin, E. P.; Sidorov, D. S.; Koshcheev, A. M.
Theoretical Foundations of Chemical Engineering (2007), 41 (5), 752-754CODEN: TFCEAU; ISSN:0040-5795. (Pleiades Publishing, Ltd.)
The oxidative dissoln. of zirconium by low-temp. chlorination in N,N-dimethylformamide-chlorine-iron(III) chloride compns. has been studied. Optimum process parameters at low chlorine concns. have been detd. The orders of reaction in iron and chlorine have been detd. The activation energy of the process has been calcd.
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Buchikhin, E. P.; Kuznetsov, A. Y.; Vidanov, V. L.; Shatalov, V. V.; Chekmarev, A. M. Nonaqueous Chlorination of Uranium Metal in Tributyl Phosphate. Radiochemistry 2005, 47, 263– 265, DOI: 10.1007/s11137-005-0084-8
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Nonaqueous Chlorination of Uranium Metal in Tributyl Phosphate
Buchikhin, E. P.; Kuznetsov, A. Yu.; Vidanov, V. L.; Shatalov, V. V.; Chekmarev, A. M.
Radiochemistry (New York, NY, United States) (2005), 47 (3), 263-265CODEN: RDIOEO; ISSN:1066-3622. (Pleiades Publishing, Inc.)
Low-temp. chlorination of uranium metal in the TBP-TCE-Cl2 systems was studied. Dissoln. of uranium in the dipolar aprotic solvent proceeds with formation of U(IV) compds. The activation energy of this process is 31.24 kJ mol-1, and relative reaction order with respect to Cl2 is 2. The effect of TBP concn. on chlorination was examd. The chlorination rate sharply increases at a water content in the TBP-TCE system of 0.2-0.6 vol %.
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31
Park, T. H.; Cho, Y. H.; Kang, B.; Kim, J. G.; Suh, K.; Kim, J.; Bae, S. E.; Kim, J. Y.; Giglio, J. J.; Jones, M. M. Constituent Analysis of Metal and Metal Oxide in Reduced SIMFuel Using Bromine-Ethyl Acetate. J. Radioanal. Nucl. Chem. 2018, 316, 1253– 1259, DOI: 10.1007/s10967-018-5841-1
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Constituent analysis of metal and metal oxide in reduced SIMFuel using bromine-ethyl acetate
Park, Tae-Hong; Cho, Young-Hwan; Kang, Byungman; Kim, Jong-Goo; Suh, Kyungwon; Kim, Jihye; Bae, Sang-Eun; Kim, Jong-Yun; Giglio, Jeffrey J.; Jones, Matthew M.
Journal of Radioanalytical and Nuclear Chemistry (2018), 316 (3), 1253-1259CODEN: JRNCDM; ISSN:0236-5731. (Springer)
We demonstrated that bromine in Et acetate can selectively sep. metallic contents in lanthanide metal-oxide mixts. for anal., which had been validated for uranium. This Br2-EtOAc dissoln. method was applied to det. the constituents of metal and metal oxide in SIMFuel (simulated oxide spent fuel) that was electrochem. reduced from oxide fuel in the molten salt. Compared with the anal. results obtained after dissolving the fuel in an acid soln., we concluded that the Br2-EtOAc method can be applied to uranium and rare earths but not to noble metals for the redn. yield detn.
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Cosstick, R. J.; Nancarrow, P. C. Estimation of Metallic Iron in Rusted Sponge-Iron: Dissolution of Iron Oxides by Bromine/Methanol. Talanta 1978, 25, 486– 488, DOI: 10.1016/0039-9140(78)80030-7
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Estimation of metallic iron in rusted sponge-iron: dissolution of iron oxides by bromine/methanol
Cosstick, R. J.; Nancarrow, P. C.
Talanta (1978), 25 (8), 486-8CODEN: TLNTA2; ISSN:0039-9140.
The soly. in Br-MeOH soln. of several Fe oxides commonly found in rusted sponge iron was examd. Oxide samples (10 mg, grain size <152 μ) were treated 20 min, and 2 h with 20 mL 5% Br-MeOH soln. at room temp. and under reflux. At room temp., <2.1% Fe dissolved, whereas 2 h reflux dissolved substantial amts. of Fe from samples of industrial mixed-oxides (9.92%), rust from steel (27.9%), and α-, β-, and γ-FeOOH (47.3, 52.9, and 41.6%, resp.), but <5% from Fe3O4, Fe2O3, and FeO samples.
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Violante, E. J. Phase Separation and Analysis of Sintered Titanium Carbide-Nickel Cermets Using Alcoholic Bromine. Anal. Chem. 1961, 33, 1600– 1602, DOI: 10.1021/ac60179a042
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Phase separation and analysis of sintered titanium carbide-nickel cermets using alcoholic bromine
Violante, Edward J.
(1961), 33 (), 1600-2CODEN: ANCHAM; ISSN:0003-2700.
Sintered TiC was sepd. from TiC-Ni cermets by treating the sample with 5% Br in abs. MeOH for 6 hrs. at -20° and occasionally stirring with a thermometer. The soln. was filtered through a weighed fritted-glass crucible, and the ppt. was washed with abs. MeOH, dried at 110°, and weighed to obtain TiC.
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Orefice, M.; Eldosouky, A.; Škulj, I.; Binnemans, K. Removal of Metallic Coatings from Rare-Earth Permanent Magnets by Solutions of Bromine in Organic Solvents. RSC Adv. 2019, 9, 14910– 14915, DOI: 10.1039/C9RA01696A
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Removal of metallic coatings from rare-earth permanent magnets by solutions of bromine in organic solvents
Orefice, Martina; Eldosouky, Anas; Skulj, Irena; Binnemans, Koen
RSC Advances (2019), 9 (26), 14910-14915CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
Successful direct recycling routes are known for both Nd-Fe-B permanent magnets and Sm-Co permanent magnets. Often the magnets are coated by a nickel-copper-nickel coating to prevent corrosion of Nd-Fe-B magnets and chipping of Sm-Co magnets. However, this coating does not contribute to the magnetic properties and only ends up as a contamination in the recycled magnet powder, which in turn dils. the magnet alloy and reduces the magnetic performance. One soln. is the addn. of virgin magnet alloy to the recycled powder, but this is not the best option from a sustainable point of view. Another option is to remove the coating prior to the magnet recycling. We developed a solvometallurgical process for removal of the metallic coating prior to direct recycling. In particular, a mixt. of bromine in org. solvents was found to be very selective in the removal of the nickel-copper-nickel coating from both Nd-Fe-B permanent magnets and Sm-Co permanent magnets, without codissoln. of the magnet alloy.
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35
Solomon, F.; Jerusalem, I. Process for Extracting Noble Metals. U.S. Patent 4,997,532, 1991.
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There is no corresponding record for this reference.
36
Bowman, P. T.; Ko, E. I.; Sides, P. J. A Potential Hazard in Preparing Bromine-Methanol Solutions. J. Electrochem. Soc. 1990, 137, 1309– 1311, DOI: 10.1149/1.2086655
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A potential hazard in preparing bromine-methanol solutions
Bowman, Paul T.; Ko, Edmond I.; Sides, Paul J.
Journal of the Electrochemical Society (1990), 137 (4), 1309-11CODEN: JESOAN; ISSN:0013-4651.
The reactivity of Br2-MeOH solns. useful in semiconductor etching and general chem. and biochem. prepns. was studied as a function of time and Br concn. 10-25 (vol./vol. %) mixts. all showed initial temp. increases followed by varying rates of temp. decrease. At higher Br concs., a second temp. increase occurred to reach the b.p. in the 25% soln. The study followed a violent explosion of a 50% vol./vol. soln. Some starting materials gave different temp. change patterns and an impurity may be involved.
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37
Nakao, Y. Dissolution of Metals in Halogen-Cetylpyridinium Halide-Benzene Systems. J. Chem. Res., Synop. 1991, 228– 229
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Dissolution of metals in halogen-cetylpyridinium halide-benzene systems
Nakao, Yukimichi
Journal of Chemical Research, Synopses (1991), (8), 228-9CODEN: JRPSDC; ISSN:0308-2342.
Many metals can be dissolved in halogen-cetylpyridinium halide-benzene systems; linear rates of dissoln. of Fe, Ni, Cu, Zn, Pd, Ag and Au are reported.
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Nakao, Y. Dissolution of Noble Metals in Halogen-Halide-Polar Organic Solvent Systems. J. Chem. Soc., Chem. Commun. 1992, 426– 427, DOI: 10.1039/C39920000426
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Dissolution of noble metals in halogen-halide-polar organic solvent systems
Nakao, Yukimichi
Journal of the Chemical Society, Chemical Communications (1992), (5), 426-7CODEN: JCCCAT; ISSN:0022-4936.
The dissoln. rates of Pd, Ag, and Au were detd. in (Cl, Br, I)-(Et4NCl, Me3NHCl, Et4NBr, KBr, KI, NaI)-(MeCN, MeOH, Me2CO) systems. The I-NaI-acetone system leached 99.3 Au and 93.5% Ag from an ore contg. 13.1 Au and 389.2 ppm Ag.
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Nakao, Y. Three Procedures of Reversible Dissolution/Deposition of Gold Using Halogen-Containing Organic Systems. Chem. Commun. 1997, 1765– 1766, DOI: 10.1039/a704171c
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Three procedures of reversible dissolution/deposition of gold using halogen-containing organic systems
Nakao, Yukimichi
Chemical Communications (Cambridge) (1997), (18), 1765-1766CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
Gold is reversibly and repeatedly dissolved and deposited under restricted conditions in a soln. consisting of an elemental halogen, a halide and acetonitrile by a procedure involving one of three phys. operations: addn. of methanol, cooling, or evapn. to dryness.
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Nakao, Y.; Sone, K. Reversible Dissolution/Deposition of Gold in Iodine-Iodide-Acetonitrile Systems. Chem. Commun. 1996, 897– 898, DOI: 10.1039/CC9960000897
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Reversible dissolution/deposition of gold in iodine-iodide-acetonitrile systems
Nakao, Yukimichi; Sone, Kozo
Chemical Communications (Cambridge) (1996), (8), 897-898CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
Gold can be dissolved on heating in iodine-iodide-acetonitrile solvent systems, where the ratio I2/I- is >0.5, as [AuI2]-, and deposited from the resulting soln. on cooling via the formation of [AuI4]-.
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Nakao, Y.; Kaeriyama, K. 5139752 Method for Extraction of Gold and Silver from Ore with a Solution Containing a Halogen, Halogenated Salt and Organic Solvent. Miner. Eng. 1993, 6, 438, DOI: 10.1016/0892-6875(93)90031-H
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Nakao, Y.; Kaeriyama, K. Quaternary Ammonium Trihalide and Method for Dissolution of Metal with Liquid Containing the Compound. U.S. Patent 5,264,191, 1993.
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43
Nakao, Y. Method for the Recovery of Gold Value. U.S. Patent 5,389,124, 1995.
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44
Bricklebank, N.; Godfrey, S. M.; McAuliffe, C. A.; Pritchard, R. G. Facile One-Step Synthesis of the Cobalt(III) and Nickel(III) Tertiary Arsine Complexes [MI₃(AsMe₃)₂] (M = Co or Ni) Directly from the Powdered Elemental Metals. J. Chem. Soc., Dalton Trans. 1996, 157– 160, DOI: 10.1039/dt9960000157
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Facile one-step synthesis of the cobalt(III) and nickel(III) tertiary arsine complex [MI3(AsMe3)2] (M = Co or Ni) directly from the powdered elemental metals
Bricklebank, Neil; Godfrey, Stephen M.; McAuliffe, Charles A.; Pritchard, Robin G.
Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry (1996), (2), 157-60CODEN: JCDTBI; ISSN:0300-9246. (Royal Society of Chemistry)
Diiodotrimethylarsine, Me3AsI2, was treated with Co or Ni metal powder to give the metal(III) complex, [MI3(AsMe3)2]. In the case of Co, a metal(II) complex, [AsMe3I][CoI3(AsMe3)], was also produced, whereas for the Ni reaction only the Ni(III) complex, [NiI3(AsMe3)2], was formed in quant. yield. The only other product from the reactions was diiodine, which was detected spectrophotometrically. Both complexes were crystallog. characterized and are isostructural, consisting of a metal(III) atom with three equatorial iodide ligands capped by two trimethylarsine ligands. These complexes are unique examples of x-ray structural characterization of compds. of this stoichiometry. Conventional wisdom would not have expected the 'soft' ligands I- and AsMe3 to bind to the relatively hard metal(III) center.
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Godfrey, S. M.; McAuliffe, C. A.; Pritchard, R. G. Inorganic Grignard Analogues. Reaction of Nickel Powder with Dihalogenotriorganophosphorus Compounds to Form Nickel-(II) and -(III) Phosphine Complexes; Isolation of Planar [Ni(PPh₃)I₃]⁻ and the Crystal Structure of [Ni(PPhMe₂)₂Br₂]. J. Chem. Soc., Dalton Trans. 1993, 2875– 2881, DOI: 10.1039/dt9930002875
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Inorganic Grignard analogs. Reaction of nickel powder with dihalogenotriorganophosphorus compounds to form nickel-(II) and -(III) phosphine complexes; isolation of planar [Ni(PPh3)I3]- and the crystal structure of [Ni(PPhMe2)2Br2]
Godfrey, Stephen M.; McAuliffe, Charles A.; Pritchard, Robin G.
Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry (1972-1999) (1993), (19), 2875-81CODEN: JCDTBI; ISSN:0300-9246.
Reactions of R3PX2 (R = Me, Et, Pr, Bu, Ph, PhCH2CH2; X = Br, I) with unactivated coarse-grain Ni metal powder were studied. The nature of the Ni phosphine complexes formed is dependent on both R and X. Where R ≠ Me and X = I [R3PI][Ni(PR3)I3] are formed, analogous to, but not isostructural with, similar Co complexes of the same stoichiometry formed from Co powder and R3PI2. Quant. electronic spectroscopic studies indicated that [R3PI][Ni(PR3)I3] all have predominantly square-planar geometry around Ni. When R = Me and X = I, [Ni(PMe3)2I3] is obtained in quant. yield, the other product being I2. Reaction of Ni powder with Me2PhPI2 yields both [Me2PhPI][Ni(PPhMe2)I3] and [Ni(PPhMe2)2I3]. These observations again mirror analogous Co reactions. Reaction of R3PBr2 with Ni powder is sensitive to the nature of R. Where R = Me, Et, or Pr no reaction occurs; where R3 = PhMe2 square-planar [Ni(PPhMe2)2Br2] and octahedral Ni(PPhMe2)2Br4 are obtained in equal yield. Where R3 = Ph2Pr octahedral [Ni(PPh2Pr)2Br4] is formed with a trace of square-planar [Ni(PPh2Pr)2Br2], and where R = Ph octahedral [Ni(PPh3)2Br4] is formed in quant. yield. [Ni(PPhMe2)2Br2] was crystallog. characterized: monoclinic, space group P21/a, a 10.018(2), b 10.249(1), c 10.138(1) Å, Z = 2, R = 0.061, R' = 0.069 (mol. centrosym.).
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Godfrey, S. M.; McAuliffe, C. A.; Pritchard, R. G. The Reaction of Bromo- and Iodo-Phosphoranes with Unactivated Coarse Grain Manganese Metal Powder to Yield [MnI₂(Phosphine)₂] and [{MnX₂(Phosphine)}_n] (X = Br or I) by Insertion of Mn into the P-X Bond. The Crystal Structure of [MnI₂(PPh₃)₂]. J. Chem. Soc., Dalton Trans. 1993, 371– 375, DOI: 10.1039/DT9930000371
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The reaction of bromo- and iodo-phosphoranes with unactivated coarse grain manganese metal powder to yield [MnI2(phosphine)2] and [{MnX2(phosphine)}n] (X = Br or I) by insertion of Mn into the P-X bond. The crystal structure of [MnI2(PPh3)2]
Godfrey, Stephen M.; McAuliffe, Charles A.; Pritchard, Robin G.
Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry (1972-1999) (1993), (3), 371-5CODEN: JCDTBI; ISSN:0300-9246.
The novel reaction of crude Mn metal powder with R3PX2 (X = Br, I) was studied. Reaction of R3PI2 (R = Ph or substituted aryl) with Mn allows insertion of Mn into P-I bonds and gives monomeric tetrahedral [MnI2(PR3)2] and MnI2. Reaction of R3PX2 (R3 = mixed aryl/alkyl, trialkyl; X = Br, I) with Mn, proceeded via insertion into P-X bonds, and leads to the quant. isolation of polymeric [{MnX2(PR3)}n], illustrating the subtle nature of these reactions. Examples of both types of complexes were crystallog. characterized and represent rare examples of such. There is some evidence that where R3 = Ph2Me an equil. exists and both types, [MnI2(PPh2Me)2] and [{MnI2(PPh2Me)}n], can be detected from the same reaction. Crystal data: [MnI2(PPh3)2]; monoclinic, space group P21/c, a 19.135(2), b 10.286(2), c 18.690(2) Å, Z = 4, R = 0.069, R' = 0.045.
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Godfrey, S. M.; McAuliffe, C. A.; Pritchard, R. G. Extreme Symbiosis: The Facile One-Step Synthesis of the Paramagnetic Cobalt(III) Complex of Triphenylantimony, Col₃(SbPh₃)₂, from the Reaction of Triphenylantimonydiiodine with Unactivated Coarse Grain Cobalt Metal Powder. J. Chem. Soc., Chem. Commun. 1994, 45– 46, DOI: 10.1039/c39940000045
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Extreme symbiosis: the facile one-step synthesis of the paramagnetic cobalt(III) complex of triphenylantimony, CoI3(SbPh3)2, from the reaction of triphenylantimony diiodine with unactivated coarse grain cobalt metal powder
Godfrey, Stephen M.; McAuliffe, Charles A.; Pritchard, Robin G.
Journal of the Chemical Society, Chemical Communications (1994), (1), 45-6CODEN: JCCCAT; ISSN:0022-4936.
Triphenylantimony diiodine (2 equiv.) reacts with unactivated cobalt powder to yield the unexpected cobalt(III) complex CoI3(SbPh3)2 (I); this five coordinate species represents a rare example of a paramagnetic cobalt(III) complex. The crystal structure of I was detd.
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48
Bricklebank, N.; Godfrey, S. M.; McAuliffe, C. A.; MacKie, A. G.; Pritchard, R. G. The X-Ray Crystal Structure of [Zn(PEt₃)I₂]₂, the First 1:1 Zinc(II) Complex of a Tertiary Phosphine of Low Steric Requirements, Prepared by the Reaction of Unactivated Zinc Metal with Diiodotriethylphosphorane. J. Chem. Soc., Chem. Commun. 1992, 944– 945, DOI: 10.1039/c39920000944
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48
The x-ray crystal structure of [Zn(PEt3)I2]2, the first 1:1 zinc(II) complex of a tertiary phosphine of low steric requirements, prepared by the reaction of unactivated zinc metal with diiodotriethylphosphorane
Bricklebank, Neil; Godfrey, Stephen M.; McAuliffe, Charles A.; Mackie, Anthony G.; Pritchard, Robin G.
Journal of the Chemical Society, Chemical Communications (1992), (13), 944-5CODEN: JCCCAT; ISSN:0022-4936.
Unactivated zinc powder reacts with R3PI2 (R = Me, Et, Pr, Bu) to yield Zn(R3P)I2 (I). The x-ray crystal structure of I (R = Et) shows it to be dimeric [Zn(PEt3)I2]2.
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Godfrey, S. M.; Ho, N.; McAuliffe, C. A.; Pritchard, R. G. The Oxidation of Gold Powder by Me₃EI₂ (E = P, As) under Ambient Conditions; Structures of [AuI₃(PMe₃)₂], [AuI₃(AsMe₃)I, and I(Me₃PO)₂H][AuI₂]. Angew. Chem., Int. Ed. Engl. 1996, 35, 2344– 2346, DOI: 10.1002/anie.199623441
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The oxidation of gold powder by Me3EI2 (E = P, As) under ambient conditions; structures of [AuI3(PMe3)2], [AuI3(AsMe3)], and [(Me3PO)2H][AuI2]
Godfrey, Stephen M.; Ho, Nicholas; McAuliffe, Charles A.; Pritchard, Robin G.
Angewandte Chemie, International Edition in English (1996), 35 (20), 2344-2346CODEN: ACIEAY; ISSN:0570-0833. (VCH)
Treatment of Au powder with Me3AsI2 or Me3PI2 under N2 for 3 days at 25° afforded [AuI3(AsMe3)] and [AuI3(PMe3)2], resp. The structures of the products were detd. by x-ray crystallog. [AuI3(AsMe3)] has a square-planar coordination geometry as expected for a d8 metal center. [AuI3(PMe3)2] has an unexpected trigonal-bipyramidal geometry. Reaction of [AuI3(PMe3)2] with water in Et2O afforded [(Me3PO)2H][AuI2], which was also characterized by single-crystal x-ray anal.
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Bigoli, F.; Deplano, P.; Mercuri, M. L.; Pellinghelli, M. A.; Pintus, G.; Serpe, A.; Trogu, E. F. A Powerful New Oxidation Agent towards Metallic Gold Powder: N,N′-Dimethylperhydrodiàzepine-2,3-Dithione (D) Bis(Diiodine). Synthesis and X-Ray Structure of [AuDI₂]I₃. Chem. Commun. 1998, 2351– 2352, DOI: 10.1039/a806158k
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A powerful new oxidation agent towards metallic gold powder: N,N'-dimethylperhydrodiazepine-2,3-dithione (D) bis(diiodine). Synthesis and X-ray structure of [AuDI2]I3
Bigoli, Francesco; Angela Pellinghelli, Maria; Deplano, Paola; Mercuri, Maria Laura; Pintus, Gloria; Serpe, Angela; Trogu, Emanuele F.
Chemical Communications (Cambridge) (1998), (21), 2351-2352CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
The oxidn. of Au powder by a new safe and powerful oxidizing reagent, the bis-diiodine adduct of N,N'-dimethylperhydrodiazepine-2,3-dithione (D), to produce [AuI2D]I3 under ambient conditions is described.
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Bigoli, F.; Deplano, P.; Mercuri, M. L.; Pellinghelli, M. A.; Pintus, G.; Serpe, A.; Trogu, E. F. N,N′-Dimethylpiperazinium-2,3-Dithione Triiodide, [Me₂pipdt]I₃, as a Powerful New Oxidation Agent toward Metallic Platinum. Synthesis and x-Ray Structures of the Reagent and the Product [Pt(Me₂pipdt)₂](I₃)₂. J. Am. Chem. Soc. 2001, 123, 1788– 1789, DOI: 10.1021/ja0056015
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N,N'-Dimethylpiperazinium-2,3-dithione Triiodide, [Me2Pipdt]I3, as a Powerful New Oxidation Agent toward Metallic Platinum. Synthesis and X-ray Structures of the Reagent and the Product [Pt(Me2Pipdt)2](I3)2
Bigoli, Francesco; Deplano, Paola; Mercuri, Maria Laura; Pellinghelli, Maria Angela; Pintus, Gloria; Serpe, Angela; Trogu, Emanuele F.
Journal of the American Chemical Society (2001), 123 (8), 1788-1789CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
N,N'-dimethylpiperazinium-2,3-dithione triiodide, (Me2Pipdt)I3, reacted with metallic Pt gave [Pt(Me2Pipdt)2](I3)2 (I). I is monoclinic, space group P21/n, Z = 2, R1 = 0.0506, wR2 = 0.1393. Square planar I has an envelope conformation. I exhibits multistep reversible electrochem. redns. [Pt(Me2Pipdt)2](BF4)2 shows 2 string absorptions in the visible region. An approx. calcn. of the frontier orbitals of the BF4- salt were performed using EHMO.
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Vanzi, M.; Bonfiglio, A.; Salaris, P.; Deplano, P.; Trogu, E. F.; Serpe, A.; Salmini, G.; De Palo, R. Gold Removal in Failure Analysis of GaAs-Based Laser Diodes. Microelectron. Reliab. 1999, 39, 1043– 1047, DOI: 10.1016/S0026-2714(99)00144-4
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Mercuri, M. L.; Serpe, A.; Marchiò, L.; Artizzu, F.; Espa, D.; Deplano, P. Effective One-Step Removal-Inertization of Hazardous Metals (Cd and Hg) by Environmental Friendly Reagents. Inorg. Chem. Commun. 2014, 39, 47– 50, DOI: 10.1016/j.inoche.2013.10.045
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Effective one-step removal-inertization of hazardous metals (Cd and Hg) by environmental friendly reagents
Mercuri, Maria Laura; Serpe, Angela; Marchio, Luciano; Artizzu, Flavia; Espa, Davide; Deplano, Paola
Inorganic Chemistry Communications (2014), 39 (), 47-50CODEN: ICCOFP; ISSN:1387-7003. (Elsevier B.V.)
[HMe2pipdt]I3 (Me2pipdt = N,N'-dimethyl-piperazine-2,3-dithione, 1) is capable to quant. dissolve elemental Cd and Hg to produce in a one-step reaction the [CdI(Me2pipdt)2](I3) (2) and [HgI2(Me2pipdt)] (3) complexes. Crystals of 2 and 3 have been structurally characterized and crystallize in the P-1 and C2/c space group, resp. In 2 Cd(II) shows a coordination geometry intermediate between the square pyramidal and the trigonal bipyramidal. In 3 Hg(II) adopts a distorted tetrahedral geometry which involves a S,S chelating ligand and two iodine atoms in the coordination sphere. Vibrational spectroscopy findings are in agreement with structural results showing in the far-IR region to be a diagnostic probe in recognizing triiodides.
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Cau, L.; Deplano, P.; Marchiò, L.; Mercuri, M. L.; Pilia, L.; Serpe, A.; Trogu, E. F. New Powerful Reagents Based on Dihalogen/N,N′- Dimethylperhydrodiazepine-2,3-Dithione Adducts for Gold Dissolution: The IBr Case. Dalt. Trans. 2003, 1969– 1974, DOI: 10.1039/B210281A
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Cuscusa, M.; Rigoldi, A.; Artizzu, F.; Cammi, R.; Fornasiero, P.; Deplano, P.; Marchiò, L.; Serpe, A. Ionic Couple-Driven Palladium Leaching by Organic Triiodide Solutions. ACS Sustainable Chem. Eng. 2017, 5, 4359– 4370, DOI: 10.1021/acssuschemeng.7b00410
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Ionic Couple-Driven Palladium Leaching by Organic Triiodide Solutions
Cuscusa, Mariangela; Rigoldi, Americo; Artizzu, Flavia; Cammi, Roberto; Fornasiero, Paolo; Deplano, Paola; Marchio, Luciano; Serpe, Angela
ACS Sustainable Chemistry & Engineering (2017), 5 (5), 4359-4370CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
Pd dissoln. capabilities of a variety of org. triiodides (OrgI3) in org. solvent, where Org+ =3,5-bis(phenylamino)-1,2-dithiolylium [(PhHN)2DTL+], 3,5-bis(morpholino)-1,2-dithiolylium (Mo2DTL+); tetrabuthylammonium (TBA+); and tetraphenylphosphonium (Ph4P+), toward the crude metal and model-spent 3-way catalyst (TWC), are described here. Enhanced Pd-leaching yields from TWC were obtained using OrgI3 solns. (≤98%) in spite of the fully inorg. KI3 one (38%) in the same mild conditions. The reaction products were isolated and characterized as Org2[Pd2I6]. Crystallog. and DFT studies highlighted the presence of several ion-pair secondary interactions in the products, which can explain the improved effectiveness of the Pd etching by OrgI3. For comparison purposes, the gold leaching by using R2DTLI3 and the obtained Au complexes were studied. Preliminary results addressed to recover the metal and the reagents from the etching product showed that (PhHN)2DTLI3 is the most promising reagent to improve sustainability in the whole process.
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Isaia, F.; Aragoni, M. C.; Arca, M.; Caltagirone, C.; Demartin, F.; Garau, A.; Lippolis, V. Gold Oxidative Dissolution by (Thioamide)-I₂ Adducts. Dalt. Trans. 2013, 42, 492– 498, DOI: 10.1039/C2DT31855E
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Serpe, A.; Artizzu, F.; Mercuri, M. L.; Pilia, L.; Deplano, P. Charge Transfer Complexes of Dithioxamides with Dihalogens as Powerful Reagents in the Dissolution of Noble Metals. Coord. Chem. Rev. 2008, 252, 1200– 1212, DOI: 10.1016/j.ccr.2008.01.024
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Charge transfer complexes of dithioxamides with dihalogens as powerful reagents in the dissolution of noble metals
Serpe, Angela; Artizzu, Flavia; Mercuri, Maria Laura; Pilia, Luca; Deplano, Paola
Coordination Chemistry Reviews (2008), 252 (10+11), 1200-1212CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
A review. Commonly involved in the recovery/refining processes of noble metals (NMs), coordination chem. is now required by new legislation to face requirements in the selection of ligands that must combine effectiveness with low environmental impact, to balance sustainability with economic development for conventional applications and for the recovery of NMs from secondary sources thus helping to convert Trash in Resource. In this paper, we review the properties of dihalogen/cyclic-dithioxamide adducts as a case-study to show how suitable complexes can provide innovation in the recovery processes of NMs from secondary sources and in the gold etching process in improving the reliability of microelectronic devices. These adducts, which do not show cytotoxicity, are capable of dissolving metal palladium and even gold in a one-step reaction and under mild conditions. In particular, Me2dazdt·2I2 (Me2dazdt = N,N'-dimethyl-perhydrodiazepine-2,3-dithione) has proved to be the most effective in practical applications. It was used in the palladium recovery from model spent three way catalysts (TWC). It selectively dissolved palladium, almost quant., under mild conditions, even in a complex system such as an exhaust catalytic converter, a ceramic material that has undergone severe thermal and chem. stresses. Quite satisfactory results were obtained in gold recovery from selected WEEE (waste from elec. and electronic equipments) scrap and from deprocessing procedures for the failure anal. of microelectronic devices.
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Serpe, A.; Marchiò, L.; Artizzu, F.; Mercuri, M. L.; Deplano, P. Effective One-Step Gold Dissolution Using Environmentally Friendly Low-Cost Reagents. Chem. - Eur. J. 2013, 19, 10111– 10114, DOI: 10.1002/chem.201300940
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Effective One-Step Gold Dissolution Using Environmentally Friendly Low-Cost Reagents
Serpe, Angela; Marchio, Luciano; Artizzu, Flavia; Mercuri, M. Laura; Deplano, Paola
Chemistry - A European Journal (2013), 19 (31), 10111-10114CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
Authors performed an extensive investigation into several potential etching candidates based on donor-acceptor mixts. in order to tailor their formations for specific applications by optimizing the safety, efficiency and selectivity of the process while limiting the energy usage and cost. They describe the case of I2 mixts. with the S-donor tetraethylthiuram disulfide (Et4TDS), which is a cheap easy to handle reagent. Acetone mixts. of I2 and Et4TDS have been shown to process amazing etching properties towards elemental Au, as both a powder or a thin layer.
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Jantan, K. A.; Kwok, C. Y.; Chan, K. W.; Marchiò, L.; White, A. J. P.; Deplano, P.; Serpe, A.; Wilton-Ely, J. D. E. T. From Recovered Metal Waste to High-Performance Palladium Catalysts. Green Chem. 2017, 19, 5846– 5853, DOI: 10.1039/C7GC02678A
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From recovered metal waste to high-performance palladium catalysts
Jantan, Khairil A.; Kwok, Chuek Yee; Chan, Kuang Wen; Marchio, Luciano; White, Andrew J. P.; Deplano, Paola; Serpe, Angela; Wilton-Ely, James D. E. T.
Green Chemistry (2017), 19 (24), 5846-5853CODEN: GRCHFJ; ISSN:1463-9262. (Royal Society of Chemistry)
The catalytic activity of neutral and cationic, homo- and heteroleptic, mono- and bimetallic Pd(II) compds. based on dithiocarbamate and dithiooxamide S,S-donor ligands is described. High activity was obsd. in the regio- and chemo-selective C-H functionalization of benzo[h]quinoline to 10-alkoxybenzo[h]quinoline and 8-methylquinoline to 8-(methoxymethyl)quinoline in the presence of the oxidant PhI(OAc)2. The best performance was found for [Pd(Me2dazdt)2]I6 (Me2dazdt = N,N'-dimethyl-perhydrodiazepine-2,3-dithione), [PdI2(Me2dazdt)] and [Pd(Cy2DTO)2]I8 (Cy2DTO = N,N'-dicyclohexyl-dithiooxamide) which are all obtained directly as products of sustainable Pd-metal leaching processes used to recover Pd from scrap metal. These compds. provided almost quant. yields under milder conditions (50°, 1 - 3 mol% Pd loading) and much shorter reaction times (1 - 3 h) than reported previously. These results illustrate how the complexes obtained from the selective and sustainable recovery of Pd from automotive heterogeneous Three Way Catalysts (TWC) can be employed directly in homogeneous catalysis, avoiding further metal recovery steps and valorising the metal complex itself in a 'circular economy' model.
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Serpe, A.; Artizzu, F.; Espa, D.; Rigoldi, A.; Mercuri, M. L.; Deplano, P. From Trash to Resource: A Green Approach to Noble-Metals Dissolution and Recovery. Green Process. Synth. 2014, 3, 141– 146, DOI: 10.1515/gps-2014-0004
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From trash to resource: a green approach to noble-metals dissolution and recovery
Serpe, Angela; Artizzu, Flavia; Espa, Davide; Rigoldi, Americo; Mercuri, Maria Laura; Deplano, Paola
Green Processing and Synthesis (2014), 3 (2), 141-146CODEN: GPSREC; ISSN:2191-9550. (Walter de Gruyter GmbH)
A process based on the lixiviant properties of org. mixts. of dihalogen/S,S-ligands, N,N'-dimethyl-perhydrodiazepine-2,3-dithione (Me2dazdt) and tetraalkylthiuramdisulfide (Et4TDS) in the presence of diiodine, for gold recovery from the non-ferrous metal fraction of real shredded waste elec. and electronic equipment (WEEE), is presented here. Selective dissoln. of metals is achieved through a sequence of three steps where the oxidn. of different kinds of metals is achieved by using: (1) refluxing water solns. of HCl 1:5 under Ar atm. (Sn, Zn, etc.); (2) water solns. of NH3/(NH4)2SO4 mixts. in the presence of H2O2 on the resting sample(Cu, Ag); and (3) acetone solns. of Me2dazdt or Et4TDS/I2 mixts. on the final residue (Au). Each step is followed by a further treatment for: (1) metal recovery, in the case of Au, Cu, Ag; and (2) inertization, in the case of heavy metals. As a whole, the process is very promising for effective recovery of gold and other valuable noble-metals and for using non harmful reagents in mild conditions.
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Serpe, A.; Bigoli, F.; Cabras, M. C.; Fornasiero, P.; Graziani, M.; Mercuri, M. L.; Montini, T.; Pilia, L.; Trogu, E. F.; Deplano, P. Pd-Dissolution through a Mild and Effective One-Step Reaction and Its Application for Pd-Recovery from Spent Catalytic Converters. Chem. Commun. 2005, 1040– 1042, DOI: 10.1039/b415799k
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Pd dissolution by a mild and effective one-step reaction, and its application for Pd recovery from spent catalytic converters
Serpe, Angela; Bigoli, Francesco; Cabras, M. Cristina; Fornasiero, Paolo; Graziani, Mauro; Mercuri, M. Laura; Montini, Tiziano; Pilia, Luca; Trogu, Emanuele F.; Deplano, Paola
Chemical Communications (Cambridge, United Kingdom) (2005), (8), 1040-1042CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
An innovative method for Pd dissoln. from scrap is based on using N,N'-dimethylperhydrodiazepine-2,3-dithione diiodide adduct (I), which is safe and powerful for practical applications. The I is suitable for nearly quant. Pd recovery by dissoln. from spent catalysts with powder or foil. The effectiveness of I is maintained when the Pd is contained in a complex system, such as automotive catalyst on a ceramic substrate that has undergone severe thermal stress.
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Cechin, C. N.; Razera, G. F.; Tirloni, B.; Piquini, P. C.; de Carvalho, L. M.; Abram, U.; Lang, E. S. Oxidation of Crude Palladium Powder by a Diiodine Adduct of (2-PyTe)₂ to Obtain the Novel PdII Complex [PdI(TePy-2)(I₂TePy-2)₂]. Inorg. Chem. Commun. 2020, 118, 107966, DOI: 10.1016/j.inoche.2020.107966
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Oxidation of crude palladium powder by a diiodine adduct of (2-PyTe)2 to obtain the novel PdII complex [PdI(TePy-2)(I2TePy-2)2]
Cechin, Camila N.; Razera, Giovanny F.; Tirloni, Barbara; Piquini, Paulo C.; de Carvalho, Leandro M.; Abram, Ulrich; Lang, Ernesto S.
Inorganic Chemistry Communications (2020), 118 (), 107966CODEN: ICCOFP; ISSN:1387-7003. (Elsevier B.V.)
[PdI(TePy-2)(I2TePy-2)2] is obtained via a rare oxidn. reaction of palladium powder by the in situ generated diiodine adduct of bis-2-pyridylditelluride at room temp. An X-ray diffraction study reveals the mol. structure of [PdI(TePy-2)(I2TePy-2)2], where the palladium atom is surrounded by an iodide and three tellurium atoms (two [I2TePy-2] and one [TePy-2] groups). The oxidn. states for the tellurium atoms were analyzed using calcd. at. charges and electron localization function (ELF). The optical band gap for [PdI(TePy-2)(I2TePy-2)2] was detd. through theor. (DFT) and exptl. (diffuse reflectance UV-Visible) studies and the electrochem. behavior for the compd. was examd. by cyclic voltammetry.
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Holthoff, J. M.; Engelage, E.; Kowsari, A. B.; Huber, S. M.; Weiss, R. Noble Metal Corrosion: Halogen Bonded Iodocarbenium Iodides Dissolve Elemental Gold—Direct Access to Gold–Carbene Complexes. Chem. - Eur. J. 2019, 25, 7480– 7484, DOI: 10.1002/chem.201901583
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Noble Metal Corrosion: Halogen Bonded Iodocarbenium Iodides Dissolve Elemental Gold-Direct Access to Gold-Carbene Complexes
Holthoff, Jana M.; Engelage, Elric; Kowsari, Alexander B.; Huber, Stefan M.; Weiss, Robert
Chemistry - A European Journal (2019), 25 (31), 7480-7484CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
A common method to dissolve elemental Au involves the combination of an oxidant with a Lewis base that coordinates to the Au surface, thus lowering the metal's redox potential. Herein the authors report the usage of org. iodide salts, which provide both oxidative power and a coordinating ligand, to dissolve Au under formation of organo-Au complexes. The obtained products were identified as AuIII complexes, all featuring Au-C bonds, as shown by x-ray single-crystal anal., and can be isolated in good yields. Addnl., the authors' method provides direct access to N-heterocyclic carbene (NHC-type) complexes and avoids costly organometallic precursors. The studied complexes show dynamic behavior in MeCN and in the case of the NHC(-type) complexes, the involved species could be identified as a monocarbene [AuI3(carbene)] and biscarbene complex [AuI2(carbene)2]+.
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Tezuka, Y.; Miya, M.; Hashimoto, A.; Imai, K. Dissolution of Copper Metal in a Dimethyl Sulfoxide-Carbon Tetrachloride Mixture. J. Chem. Soc., Chem. Commun. 1987, 1642– 1643, DOI: 10.1039/C39870001642
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Dissolution of copper metal in a dimethyl sulfoxide-carbon tetrachloride mixture
Tezuka, Yasuyuki; Miya, Masamitsu; Hashimoto, Akio; Imai, Kiyokazu
Journal of the Chemical Society, Chemical Communications (1987), (21), 1642-3CODEN: JCCCAT; ISSN:0022-4936.
Cu metal dissolves in a DMSO-CCl4 mixt. under extremely mild conditions with the formation of CuCl2(DMSO)2 and Me2S. HCl, CuCl, and CuCl2 reduce the induction period and other halocarbon compds. can be substituted for CCl4. A mechanism is proposed.
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Egorov, A. M.; Matyukhova, S. A.; Anisimov, A. V. Kinetics and Mechanism of the Reaction of Carbon Tetrachloride with Copper in Dimethylacetamide. Kinet. Catal. 2003, 44, 471– 475, DOI: 10.1023/A:1025129731071
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Kinetics and Mechanism of the Reaction of Carbon Tetrachloride with Copper in Dimethylacetamide
Egorov, A. M.; Matyukhova, S. A.; Anisimov, A. V.
Kinetics and Catalysis (Translation of Kinetika i Kataliz) (2003), 44 (4), 471-475CODEN: KICAA8; ISSN:0023-1584. (MAIK Nauka/Interperiodica Publishing)
The reaction of copper with carbon tetrachloride in dimethylacetamide was studied. In the absence of atm. oxygen, the oxidative dissoln. of copper occurred by the mechanism of single-electron transfer with the formation of C2Cl6 and copper(I) complexes. The kinetic and thermodn. parameters of the reaction were found. The reaction mechanism is discussed.
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Egorov, A. M.; Matyukhova, S. A.; Uvarova, N. V.; Anisimov, A. V. Kinetics and Mechanism of the Reaction of Benzyl Bromide with Titanium in Dimethylformamide. Russ. J. Gen. Chem. 2005, 75, 1445– 1451, DOI: 10.1007/s11176-005-0443-3
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Kinetics and Mechanism of the Reaction of Benzyl Bromide with Titanium in Dimethylformamide
Egorov, A. M.; Matyukhova, S. A.; Uvarova, N. V.; Anisimov, A. V.
Russian Journal of General Chemistry (2005), 75 (9), 1445-1451CODEN: RJGCEK; ISSN:1070-3632. (Pleiades Publishing, Inc.)
The reaction of titanium with benzyl bromide in DMF was studied. No reaction occurs in the presence of atm. oxygen. Under oxygen-free conditions, the oxidative dissoln. of titanium occurs by the mechanism of 1-electron transfer with the formation of 1,2-diphenylethane and Ti(IV) complexes. The kinetic and thermodn. parameters of the process were detd. The reaction mechanism was discussed.
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Yanagihara, N.; Nakayama, M.; Tai, H. A Potent Solvent for Dissolution of Metallic Copper. Chem. Lett. 2003, 32, 640– 641, DOI: 10.1246/cl.2003.640
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A potent solvent for dissolution of metallic copper
Yanagihara, Naohisa; Nakayama, Masahiro; Tai, Hideo
Chemistry Letters (2003), 32 (7), 640-641CODEN: CMLTAG; ISSN:0366-7022. (Chemical Society of Japan)
Metallic copper was found to dissolve in a mixt. of ammonia and carbon tetrachloride under extremely mild conditions. The solubilized copper was detd. to be in the form of an ammine complex of copper(II) chloride, [Cu(NH3)m]Cl2·nH2O.
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Jackson, N. R. C.; Harrison, W. D.; Goodall, D. C. New Reactions of Precious Metals and Their Binary Compounds in Solvents Containing Carbon Halides. J. Chem. Soc., Chem. Commun. 1988, 729– 730, DOI: 10.1039/c39880000729
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New reactions of precious metals and their binary compounds in solvents containing carbon halides
Jackson, Neale R. C.; Harrison, W. David; Goodall, David C.
Journal of the Chemical Society, Chemical Communications (1988), (11), 729-30CODEN: JCCCAT; ISSN:0022-4936.
Several precious metals and their binary compds. react with CCl4, CBr4, CPh2Cl2, CPhCl3, or C(CN)2Cl2 in DMSO, DMF or dimethylacetamide, and with C halides in EtOH or AcH contg. added ligand.
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van Meersbergen, M. T.; Lorenzen, L.; van Deventer, J. S. J. The Electrochemical Dissolution of Gold in Bromine Medium. Miner. Eng. 1993, 6, 1067– 1079, DOI: 10.1016/0892-6875(93)90075-X
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The electrochemical dissolution of gold in bromine medium
van Meersbergen, M.T.; Lorenzen, L.; van Deventer, J.S.J.
Minerals Engineering (1993), 6 (8-10), 1067-1079CODEN: MENGEB; ISSN:0892-6875.
Two rotating disc electrodes, either in the same container or in two sep. containers linked by a salt-bridge were used in this investigation. The leaching behavior of gold in contact or in assocn. with various minerals depends largely on the galvanic interaction between gold and the mineral, and partly on the formation of a film on the gold surface. Copper, iron and galena cause the largest decrease in the rate of leaching when in contact with gold. This can be mainly attributed to the galvanic interaction between the two substances. Sphalerite strongly enhances the dissoln. rate due to the action of dissolved Zn2+ ions on the surface of the gold. When these Zn2+ are prevented from coming into contact with the gold, sphalerite still enhances the gold leaching rate owing to film formation on the gold surface which probably increased its cond. Gold in contact with pyrite also enhances the gold dissoln. rate significantly.
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Kokoreva, S. G.; Shirshova, L. V.; Kir’yakov, N. V.; Shul’ga, Y. U. M.; Lavrent’ev, I. P. Specific Features of the Interaction of Components in the DMSO-HBr-Pd⁰ System. Russ. Chem. Bull. 2000, 49, 1722– 1725, DOI: 10.1007/BF02496341
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Specific features of the interaction of components in the DMSO-HBr-Pd0 system
Kokoreva, S. G.; Shirshova, L. V.; Kir'yakov, N. V.; Shul'ga, Yu. M.; Lavrent'ev, I. P.
Russian Chemical Bulletin (Translation of Izvestiya Akademii Nauk, Seriya Khimicheskaya) (2000), 49 (10), 1722-1725CODEN: RCBUEY; ISSN:1066-5285. (Consultants Bureau)
The products of interaction of components in the donor-acceptor electron-transport (DAET) DMSO-HBr system and their complex formation with the metallic Pd surface were studied. H2O and Me2S (main reaction products) and CO, CS2, C2H6, MeBr, H, and CH4 (minor reaction products) were found in the gas phase by mass spectrometry (MS). The samples of metallic Pd treated with the DAET system with a components ratio corresponding to the min. and max. rates of metal dissoln. were studied by the methods of thermo-programmed desorption with MS detection (TPD-MS) and XPS. According to the TPD-MS data, two forms of Me2S are present on the metal surface, whereas the XPS method detected two complexes with the mol. compns. Pd11Br4S1.26 and Pd11Br3.86S1.42. The addn. of an aq. soln. of NaOH to the system gave HCOONa, which indicates that compds. (CH2O, HCOOH) capable of reducing the Pd complexes are present in the DAET system.
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Shirshova, L. V.; Lavrent’ev, I. P. Synthesis of Silver Complexes in DMSO-HX and DMSO-HX-Ketone Systems. Russ. J. Coord. Chem. 2001, 27, 511– 515, DOI: 10.1023/A:1011397801630
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Synthesis of silver complexes in DMSO-HX and DMSO-HX-ketone systems
Shirshova, L. V.; Lavrent'ev, I. P.
Russian Journal of Coordination Chemistry (Translation of Koordinatsionnaya Khimiya) (2001), 27 (7), 511-515CODEN: RJCCEY; ISSN:1070-3284. (MAIK Nauka/Interperiodica Publishing)
Comparative anal. of the oxidizing and complexing properties of the DMSO-HX (X = Cl, Br, I) and DMSO-HX-ketone (X = Br, I: the ketone is acetone, acetylacetone, or acetophenone) systems toward Ag was performed. The reaction products are AgX (X = Cl, Br, I), [Me3S+]AgnX-m (n = 1, 2; m = 2, 3; X = Br, I) and [Me2S+CH2COR]AgX-2 (R = Me, Ph; X = Br, I). The compn. of the obtained complexes depends on both the DMSO:HX ratio and the nature of HX, as well as on the methods used to isolate solid products from the soln. The formation of the [Me2S+CH2COMe]AgBr-2 complex in the Ag0-DMSO-HBr-acetylacetone system occurs with cleavage of the acetylacetone C-C bond and follows a specific reaction course. The optimum conditions for prodn. of the Ag compds. in the title systems are detd.
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Shirshova, L. V.; Kokoreva, S. G.; Lavrentév, I. P. Dissolution of Noble Metals and Copper in the DMSO-HBr_aq System. Russ. Chem. Bull. 2008, 57, 2447– 2451, DOI: 10.1007/s11172-008-0351-x
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Dissolution of noble metals and copper in the DMSO-HBraq system
Shirshova, L. V.; Kokoreva, S. G.; Lavrentev, I. P.
Russian Chemical Bulletin (2008), 57 (12), 2447-2451CODEN: RCBUEY; ISSN:1066-5285. (Springer)
The processes occurring in the DMSO-HBraq system at different ratios of the components were studied by electronic and IR spectroscopy. The interaction of the components in the system results in the accumulation and consumption as oxidants of Br-contg. (Me2S(OH)Br, Me2S·Br2) and O-contg. compds. (H2O2, HBrO). It was shown by the pH-metric method that the equil. concn. of species that are accumulated in the system and oxidize the metal is achieved on the 5th day after mixing of the components. The dependence of the dissoln. rate of Pt (Pt0) on the ratio of components (DMSO: HBr) has three maxima, whose positions are detd. by the nature of intermediate species formed in the system and the state of the metal surface contg. the oxide film.
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Shirshova, L. V.; Lavrent’ev, I. P.; Kokoreva, S. G. The Study of Copper Dissolution in Aqueous and Nonaqueous Systems DMSO-HX_solv (Solv = H₂O, X = Br, Cl; Solv = MeCN, PhNO₂; X = Cl) by Resistometric Method. Russ. Chem. Bull. 2010, 59, 1692– 1697, DOI: 10.1007/s11172-010-0298-6
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The study of copper dissolution in aqueous and nonaqueous systems DMSO-HXsolv (solv = H2O, X = Br, Cl; solv = MeCN, PhNO2; X = Cl) by resistometric method
Shirshova, L. V.; Lavrent'ev, I. P.; Kokoreva, S. G.
Russian Chemical Bulletin (2010), 59 (9), 1692-1697CODEN: RCBUEY; ISSN:1066-5285. (Springer)
Copper dissoln. in the aq. systems DMSO-HXsolv (solv = H2O; X = Cl, Br) under the inert atm. and under aerobic conditions at different acid concns. was studied by the resistometric method by measuring the resistance of a metal sample in the course of the reaction. The overall activity of the system decreases with a decrease in the concn. of the starting hydrohalic acid. The rate of copper dissoln. in the extremum points also decreases. The process of the metallic copper dissoln. in nonaq. systems, such as DMSO-HClsolv (solv = MeCN, PhNO2), was studied. In the latter systems, as opposed to aq. systems, only one max. in the plot of the copper dissoln. rate vs. the component ratio is obsd. The change in the nature of the solvent in the donor-acceptor electron transport system DMSO-HClsolv (solv = H2O, MeCN, PhNO2) results in the change in the position of the max. of the copper dissoln. rate, as well as in the change in its value. The rate of copper dissoln. in the above mentioned systems varies in the following series: H2O < MeCN < PhNO2.
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Shirshova, L. V.; Lavrentiev, I. P. Dissolution of Copper and Gold in the Donor-Acceptor Systems DMSO−NH₄X_aq (X = Cl, Br, and I) and NH₄I_Aq−O₂. Russ. Chem. Bull. 2012, 61, 1063– 1068, DOI: 10.1007/s11172-012-0144-0
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Dissolution of copper and gold in the donor-acceptor systems DMSO-NH4Xaq (X = Cl, Br, and I) and NH4Iaq-O2
Shirshova, L. V.; Lavrentiev, I. P.
Russian Chemical Bulletin (2012), 61 (6), 1063-1068CODEN: RCBUEY; ISSN:1066-5285. (Springer)
The dependences of the dissoln. rate of Cu on the ratio of components of the liq. phase (DMSO and NH4Xaq, where NH4Xaq is an aq. soln. of NH4X; X = Cl, Br, and I) were studied in aq.-org. donor-acceptor systems DMSO-NH4Xaq systems by the resistometric method. The method involves measurements of the electroresistance of a metal sample in the reaction. The pattern of the dependences obsd. under the conditions of free air access shows that the process rates maximize at the molar ratio of the components NH4X: DMSO = 0.05: 0.95 (X = Cl, Br, and I) and minimize at the ratio 0.5: 0.5 (for X = Cl and Br). The 2nd max. is detected at the ratio NH4I: DMSO = 0.8: 0.2 for the DMSO-NH4Iaq system. The inorg. donor-acceptor system NH4Iaq-O2 was found to efficiently dissolve Cu and Au.
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Harrison, W. D.; Gill, J. B.; Goodall, D. C. Direct Reaction of Metals with the Mixed Non-Aqueous System Dimethyl Sulfoxide-Sulphur Dioxide. J. Chem. Soc., Chem. Commun. 1976, 540– 541, DOI: 10.1039/C39760000540
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Direct reaction of metals with mixed nonaqueous system dimethyl sulfoxide-sulfur dioxide
Harrison, W. David; Gill, J. Bernard; Goodall, David C.
Journal of the Chemical Society, Chemical Communications (1976), (14), 540-1CODEN: JCCCAT; ISSN:0022-4936.
Mg, V, Mn, Fe, Co, Ni, Cu, Zn, Al, In, and Yb dissolved in nonaq. Me2SO-SO2 to give the pyrosulfates, Sr, Ba, and Pb formed the sulfates, and Na, Be, Ca, Ce, Pr, Eu, Dy, Ga, Tl, Sn, Sb, Bi, I, and Cd dissolved but the products were not characterized. Phase studies indicated the existence of a 1:1 adduct of Me2SO and SO2 which was considered responsible for the soln. of metals in the system.
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Jeffreys, B.; Gill, J. B.; Goodall, D. C. Reactions in Mixed Non-Aqueous Systems Containing Sulphur Dioxide. Part 6. The Reaction of Metal Oxides with Dimethyl Sulfoxide-Sulphur Dioxide. J. Chem. Soc., Dalton Trans. 1985, 99– 100, DOI: 10.1039/DT9850000099
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Reactions in mixed nonaqueous systems containing sulfur dioxide. Part 6. The reaction of metal oxides with dimethyl sulfoxide-sulfur dioxide
Jeffreys, Brian; Gill, J. Bernard; Goodall, David C.
Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry (1972-1999) (1985), (1), 99-100CODEN: JCDTBI; ISSN:0300-9246.
Reaction of MgO, MnO2, CoO, CuO, Cu2O, ZnO, V2O5, and CrO3 in DMSO satd. with SO2 for ≤2 days gave [M(DMSO)6][S2O7] (M = Mg, Mn, Co, Cu, Zn), [V2(DMSO)12][S2O7]3, and [Cr2(DMSO)24][S2O7]3, resp. Under similar conditions SnO2, PbO2, La2O3, and Ag2O gave products of indeterminate compn., whereas TiO2, Cr2O3, Fe2O3, Co3O4, NiO, MoO3, and Al2O3 did not react. A reaction mechanism is proposed involving initial direct conversion of oxide into sulfite, followed by solvation by SO2 to disulfite and oxidn. of the latter by DMSO to metal disulfate.
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Graham, N. K.; Gill, J. B.; Goodall, D. C. Reactions in Mixed Non-Aqueous Systems Containing Sulphur Dioxide. Part 3. The Electrolytic Dissolution of Metals. J. Chem. Soc., Dalton Trans. 1983, 1363– 1365, DOI: 10.1039/dt9830001363
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77
Reactions in mixed nonaqueous systems containing sulfur dioxide. Part 3. The electrolytic dissolution of metals
Graham, Nigel K.; Gill, J. Bernard; Goodall, David C.
Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry (1972-1999) (1983), (7), 1363-5CODEN: JCDTBI; ISSN:0300-9246.
The metals Mg, Cr, W, Fe, Ni, Cu, Zn, Hg, Al, Sn, and Pb dissolve electrolytically in the mixed nonaq. solvents SO2-Me2SO, -DMF, -MeCN, -Me2CO, or -PhNO2 to form solns. contg. several S anions. Reactions of Mg, Cr, Fe, Cu, and Zn with Me2SO-SO2 give pure single products of metal disulfates. The relation between solvent parameters and metal reactivity is discussed.
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78
Harrison, W. D.; Gill, J. B.; Goodall, D. C. Reactions in Mixed Non-Aqueous Systems Containing Sulphur Dioxide. Part 1. The Dissolution of Main-Group Metals in the Binary Mixture Dimethyl Sulfoxide-Sulphur Dioxide. J. Chem. Soc., Dalton Trans. 1978, 1431– 1433, DOI: 10.1039/DT9780001431
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78
Reactions in mixed nonaqueous systems containing sulfur dioxide. Part 1. The dissolution of main-group metals in the binary mixture dimethyl sulfoxide-sulfur dioxide
Harrison, W. David; Gill, J. Bernard; Goodall, David C.
Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry (1972-1999) (1978), (11), 1431-3CODEN: JCDTBI; ISSN:0300-9246.
Mg, Al, In, and Sn reacted with a DMSO-SO2 mixt. to give ML6(S2O7)n (L = DMSO; M = Mg, n = 1; M = Sn, n = 2) and M2L12(S2O7)3 (M = Al, In), characterized by chem. anal.and IR spectra. The Raman spectra of DMSO, SO2 and the DMSO-SO2 mixt. showed the existence of a 1:1 adduct of DMSO and SO2 responsible for the reactions with metals of the system. A mechanism for oxidn. of SO2 is discussed. In the SO2-DMSO mixt. Sr, Ba, and Pb form metal sulfates but no products could be isolated.
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Harrison, W. D.; Gill, J. B.; Goodall, D. C. Reactions in Mixed Non-Aqueous Systems Containing Sulphur Dioxide. Part 2. The Dissolution of Transition Metals in the Binary Mixture Dimethyl Sulfoxide-Sulphur Dioxide, and Ion-Pair Formation Involving the Sulphoxylate Radical Ion in Mixed Solvents Cont. J. Chem. Soc., Dalton Trans. 1979, 847– 850, DOI: 10.1039/DT9790000847
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79
Reactions in mixed nonaqueous systems containing sulfur dioxide. Part 2. The dissolution of transition metals in the binary mixture dimethyl sulfoxide-sulfur dioxide, and ion-pair formation involving the sulfoxylate radical ion in mixed solvents containing sulfur dioxide
Harrison, W. David; Gill, J. Bernard; Goodall, David C.
Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry (1972-1999) (1979), (5), 847-50CODEN: JCDTBI; ISSN:0300-9246.
Transition metals react with Me2SO-SO2 to form [TiL6][S2O7]2 (L = Me2SO), [V2L12][S2O7]3, and [ML6][S2O7] (M = Mn, Fe, Co, Ni, Cu, Zn, Cd), which were characterized by elemental anal., thermogravimetric anal., and IR spectroscopy. Ce, Pr, Eu, Dy, or U also dissolve in the mixed solvent, but the products could not be characterized. The SO2- radical ion and ion pairs contg. a metal ion and SO2- exist in solns. of Li, Na, Ca, Mg, Fe, and Zn in nonaq. solvents (e.g. Me2SO, DMF, Me3PO4) contg. SO2. A correlation was established between dielec. const., donor no., and reactivity of metals in solvents contg. SO2.
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Graham, N. K.; Gill, J. B.; Goodall, D. C. Reactions in Mixed Non-Aqueous Systems Containing Sulfur Dioxide. V The Formation of Metal Sulfur Oxyanion Compounds by the Electrolytic Solution of Metals. Aust. J. Chem. 1983, 36, 1991– 1995, DOI: 10.1071/CH9831991
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Reactions in mixed non-aqueous systems containing sulfur dioxide. V. The formation of metal sulfur oxyanion compounds by the electrolytic [dis]solution of metals
Graham, Nigel K.; Gill, J. Bernard; Goodall, David C.
Australian Journal of Chemistry (1983), 36 (10), 1991-5CODEN: AJCHAS; ISSN:0004-9425.
The metals Ti, Zr, V, Cr, Mo, Fe, Ni and Sn dissolve electrolytically in the binary solvent system Me2SO-SO2, forming metal disulfates; W forms a sulfate. The metals dissolve electrolytically in other binary systems contg. SO2, forming mixts. of S oxyanions. The importance of solvent parameters in metal reactivity is discussed, together with the mechanism of the reactions.
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Gill, J. B.; Goodall, D. C.; Harrison, W. D. Reactions in Mixed Non-Aqueous Solution Containing Sulphur Dioxide. Part 9. Mechanisms of Dissolution of Metals, Oxides, and Sulphites. J. Chem. Soc., Dalton Trans. 1987, 2995– 2997, DOI: 10.1039/dt9870002995
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81
Reactions in mixed non-aqueous solution containing sulfur dioxide. Part 9. Mechanisms of dissolution of metals, oxides, and sulfites
Gill, J. Bernard; Goodall, David C.; Harrison, W. David
Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry (1972-1999) (1987), (12), 2995-7CODEN: JCDTBI; ISSN:0300-9246.
A new mechanistic pathway which explains the dissoln. of metals into binary mixts. of SO2 and DMSO is presented. The adduct, DMSO.2SO2, which is a component of these mixts. contains the S-O-S linkage necessary to the formation of [S2O7]2-. The process must proceed through free-radical electron transfer and a series of O-atom transfer steps. The reactions of metal oxides and sulfites with DMSO-SO2 conform to this mechanistic scheme.
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Gill, J. B.; Goodall, D. C.; Harrison, W. D. The Solution of Metals in Dimethyl Sulfoxide and Other Non-Aqueous Solvents Containing Sulphur Dioxide. Hydrometallurgy 1981, 6, 347– 351, DOI: 10.1016/0304-386X(81)90051-7
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The solution of metals in dimethyl sulfoxide and other nonaqueous solvents containing sulfur dioxide
Gill, J. B.; Goodall, D. C.; Harrison, W. D.
Hydrometallurgy (1981), 6 (3-4), 347-51CODEN: HYDRDA; ISSN:0304-386X.
Mg, Al, In, Sn, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, and Cd react with the mixed nonaq. system dimethyl sulfoxide (dmso) [67-68-5]-SO2 to form metal disulfates as final products. Sr, Ba, and Pb react with the same system to form metal sulfates. Li, Na, Be, Ca, Ga, Tl, Sb, Bi, Ce, Pr, Eu, Dy, U dissolve in the mixed solvent, but it has not been possible to characterize the final products, although intermediate dithionite formation was obsd. Evidence indicates the existence of a 1:1 adduct of dmso and SO2, which is considered responsible for the reaction of metals with the system. A likely mechanism for the oxidative process is discussed. The existence of the [SO2]- radical ion, and of ion-pairs contg. a metal ion and [SO2]- was demonstrated for solns. of metals in various solvents contg. SO2. The reactivity of metals in such solvents contg. SO2 was related to dielec. const. and donor no. of the solvent. Several oxides also react with the mixed solvents. [SO2]- can be generated by electrolysis in the mixed solvents.
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Gill, J. B.; Goodall, D. C.; Jeffreys, B. Reactions in Mixed Non-Aqueous Solutions Containing Sulphur Dioxide. Part 8. Phase Studies of Sulphur Dioxide-Dimethyl Sulfoxide and Sulphur Dioxide-Dimethylformamide Mixtures. J. Chem. Soc., Dalton Trans. 1986, 2603– 2605, DOI: 10.1039/DT9860002603
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Reactions in mixed non-aqueous solutions containing sulfur dioxide. Part 8. Phase studies of sulfur dioxide-dimethyl sulfoxide and sulfur dioxide-dimethylformamide mixtures
Gill, J. Bernard; Goodall, David C.; Jeffreys, Brian
Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry (1972-1999) (1986), (12), 2603-5CODEN: JCDTBI; ISSN:0300-9246.
The phase diagrams are given for the complete range of compns. of SO2-DMSO and SO2-DMF. These mixt. contain compds. of compns. 2SO2.DMSO and SO2.DMSO, identifiable as solids at -74 and -39°, but no compd. of compn. SO2.2DMSO was found which was stable as a solid. The SO2-DMF mixts. contain 3 stable solid species: 2SO2.DMF; SO2.DMF; SO2.DMF (m. -65, -60, and -40°, resp.).
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Lin, W.; Zhang, R. W.; Jang, S. S.; Wong, C. P.; Hong, J. Il. Organic Aqua Regia-Powerful Liquids for Dissolving Noble Metals. Angew. Chem., Int. Ed. 2010, 49, 7929– 7932, DOI: 10.1002/anie.201001244
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"Organic Aqua Regia"-Powerful Liquids for Dissolving Noble Metals
Lin, Wei; Zhang, Rong-Wei; Jang, Seung-Soon; Wong, Ching-Ping; Hong, Jung-Il
Angewandte Chemie, International Edition (2010), 49 (43), 7929-7932, S7929/1-S7929/32CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
The authors present results on dissoln. of noble metals in simple mixts. of thionyl chloride (SOCl2) with pyridine or with N,N-dimethylformamide. The possible mechanism of dissoln. of Au in SOCl2-pyridine mixts. includes the formation of SOCl2-pyridine charge-transfer complex which activates SOCl2 to oxidize Au. Extensive XPS, Raman, FTIR, NMR, UV-vis, and mass-spectroscopy studies of these system reveal the formation of [AuCl4]-, 1-(chlorosulfinyl)pyridinium chloride, and 4-chloropyridine oligomers. Data are presented on dissoln. of Au by SOCl2-DMF mixts. as well as on selective dissoln. of Au, Pd, and Pt on Si substrate by sequential treatment in SOCl2-DMF and SOCl2-pyridine mixts. SOCl2-pyridine vapor etching process of circuit boards is also illustrated.
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Lin, W. Organic Aqua Regia: Discovery, Fundamentals, and Potential Applications. In Noble Metals; Su, Y.-H., Ed.; InTech, 2012; pp 335– 352.
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Lin, W. Recovery of High-Purity Pt from Pt-Au Bimetallic Nanoparticles Using Organic Aqua Regia. Rare Met. 2012, 31, 92– 95, DOI: 10.1007/s12598-012-0469-8
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Recovery of high-purity Pt from Pt-Au bimetallic nanoparticles using organic aqua regia
Lin, Wei
Rare Metals (Beijing, China) (2012), 31 (1), 92-95CODEN: RARME8; ISSN:1001-0521. (Journal Publishing Center of University of Science and Technology Beijing)
Using org. aqua regia, a recently discovered powerful org. leaching agent, an effective process of recovering Pt directly from Pt-Au bimetallic nanoparticles was demonstrated. The purities of the Pt recovered from a mixt. of Au and Pt nanoparticles and from Pt-Au core-shell nanoparticle catalyst are as high as (99.49±0.22) %, and (95.02±0.08) %, resp. The novel recovery process promises applications in catalysis industry.
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Zhao, J.; Wang, B.; Xu, X.; Yu, Y.; Di, S.; Xu, H.; Zhai, Y.; He, H.; Guo, L.; Pan, Z.; Li, X. Alternative Solvent to Aqua Regia to Activate Au/AC Catalysts for the Hydrochlorination of Acetylene. J. Catal. 2017, 350, 149– 158, DOI: 10.1016/j.jcat.2017.02.027
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Alternative solvent to aqua regia to activate Au/AC catalysts for the hydrochlorination of acetylene
Zhao, Jia; Wang, Bolin; Xu, Xiaolong; Yu, Yi; Di, Shuxia; Xu, Hao; Zhai, Yuanyuan; He, Haihua; Guo, Lingling; Pan, Zhiyan; Li, Xiaonian
Journal of Catalysis (2017), 350 (), 149-158CODEN: JCTLA5; ISSN:0021-9517. (Elsevier Inc.)
In this paper, we demonstrate that the less toxic, relatively safe, and recyclable org. aqua regia (OAR) can be employed as a greener alternative solvent to conventional aqua regia to activate Au/AC catalysts for the hydrochlorination of acetylene. We show that Au-based catalysts prepd. with HAuCl4 as precursor can be prepd. initially in water (Au(H2O)/AC). Although catalysts prepd. from aq. HAuCl4 showed poor activity, it can be significantly enhanced by catalyst activation in OAR (Au(H2O)/AC(OAR)). In contrast to the catalyst activation procedure using aqua regia (Au(aq)/AC), we demonstrate that the new activation procedure leads to both improved activity and stability of the resulting Au(H2O)/AC(OAR) catalyst. Further analyses of X-ray diffraction (XRD), transmission electron microscopy (TEM), and XPS show that the variations of Au particle size and chem. state caused by OAR treatment promote Au oxidn. and high dispersion. In addn., temp.-programmed redn. (TPR) and temp.-programmed desorption (TPD) indicated that the presence of residual sulfur and nitrogen species may help stabilize the cationic Au3+ species and generate a catalyst less prone to deactivation by increasing the redn. temp. of the Au3+ species and enhancing the adsorption of hydrogen chloride over the Au(H2O)/AC(OAR) catalyst. These results suggest that OAR can be substituted for conventional solvents to activate Au/AC catalysts for the hydrochlorination of acetylene.
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Binnemans, K. Lanthanides and Actinides in Ionic Liquids. Chem. Rev. 2007, 107, 2592– 2614, DOI: 10.1021/cr050979c
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Lanthanides and Actinides in Ionic Liquids
Binnemans, Koen
Chemical Reviews (Washington, DC, United States) (2007), 107 (6), 2592-2614CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
A review is proposed considering solvation, soly., and chem. reactivity of lanthanide or actinide ions and complexes in ionic liqs., including treatment of spent nuclear fuel.
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Zhang, S.; Sun, J.; Zhang, X.; Xin, J.; Miao, Q.; Wang, J. Ionic Liquid-Based Green Processes for Energy Production. Chem. Soc. Rev. 2014, 43, 7838– 7869, DOI: 10.1039/C3CS60409H
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Ionic liquid-based green processes for energy production
Zhang, Suojiang; Sun, Jian; Zhang, Xiaochun; Xin, Jiayu; Miao, Qingqing; Wang, Jianji
Chemical Society Reviews (2014), 43 (22), 7838-7869CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
To mitigate the growing pressure on resource depletion and environment degrdn., the development of green processes for the prodn. of renewable energy is highly required. As a class of novel and promising media, ionic liqs. (ILs) have shown infusive potential applications in energy prodn. Aiming to offer a crit. overview regarding the new challenges and opportunities of ILs for developing green processes of renewable energy, this article emphasizes the role of ILs as catalysts, solvents, or electrolytes in three broadly interesting energy prodn. processes from renewable resources, such as CO2 conversion to fuels and fuel additives, biomass pretreatment and conversion to biofuels, as well as solar energy and energy storage. It is expected that this article will stimulate a generation of new ideas and new technologies in IL-based renewable energy prodn.
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Schuur, B.; Brouwer, T.; Smink, D.; Sprakel, L. M. J. Green Solvents for Sustainable Separation Processes. Curr. Opin. Green Sustain. Chem. 2019, 18, 57– 65, DOI: 10.1016/j.cogsc.2018.12.009
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There is no corresponding record for this reference.
91
Rogers, R. D.; Seddon, K. R. Ionic Liquids - Solvents of the Future?. Science (Washington, DC, U. S.) 2003, 302, 792– 793, DOI: 10.1126/science.1090313
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Chemistry. Ionic liquids--solvents of the future?
Rogers Robin D; Seddon Kenneth R
Science (New York, N.Y.) (2003), 302 (5646), 792-3 ISSN:.
There is no expanded citation for this reference.
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Li, X.; Kersten, S. R. A.; Schuur, B. Efficiency and Mechanism of Demulsification of Oil-in-Water Emulsions Using Ionic Liquids. Energy Fuels 2016, 30, 7622– 7628, DOI: 10.1021/acs.energyfuels.6b01415
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Efficiency and Mechanism of Demulsification of Oil-in-Water Emulsions Using Ionic Liquids
Li, Xiaohua; Kersten, Sascha R. A.; Schuur, Boelo
Energy & Fuels (2016), 30 (9), 7622-7628CODEN: ENFUEM; ISSN:0887-0624. (American Chemical Society)
13 Ionic liqs. (ILs), including 9 halide ILs and 4 nonhalide ILs, were evaluated as demulsifiers for a model oil-in-water emulsion prepd. with heptane and water, where sodium dodecylbenzenesulfonate (SDBS) was used as a surfactant. The sepg. efficiency (the fraction of heptane that has phase sepd. from the emulsion) of ILs was studied using bottle tests and tube tests. Bottle tests show that halide ILs exhibited very fast demulsification, and among nonhalide ILs, only trihexyltetradecylphosphonium dicyanamide (P666,14[N(CN)2]) could demulsify effectively but slower than halide ILs. Tube tests suggest that the demulsification efficiency is correlated with the mole ratio of IL and SDBS. For all ILs showing effective demulsification, instead of the desired extn. of the surfactant to an IL phase, the demulsification mechanism was ion exchange between IL anions and DBS, driven by the large Gibbs energy of hydration of the anions of the sodium salts that dissolve in water. Regeneration of these ILs and surfactants requires water-free reversed ion exchange processes with sodium salts and with salts contg. the IL anions, probably limiting com. applicability of the use of these ILs for demulsification.
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Li, X.; Kersten, S. R. A.; Schuur, B. Extraction of Guaiacol from Model Pyrolytic Sugar Stream with Ionic Liquids. Ind. Eng. Chem. Res. 2016, 55, 4703– 4710, DOI: 10.1021/acs.iecr.6b00100
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Extraction of Guaiacol from Model Pyrolytic Sugar Stream with Ionic Liquids
Li, Xiaohua; Kersten, Sascha R. A.; Schuur, Boelo
Industrial & Engineering Chemistry Research (2016), 55 (16), 4703-4710CODEN: IECRED; ISSN:0888-5885. (American Chemical Society)
Pyrolytic sugars can be converted to bioethanol or valuable platform chems. through fermn. However, the arom. contaminants need to be removed from the sugar stream before the refinery. The use of liq.-liq. extn. with ionic liqs. (ILs) for this sepn. was investigated using a model system comprising aq. levoglucosan solns. with a guaiacol impurity. The extn. performances of 41 ILs were simulated using COSMO-RS. The simulation results demonstrated that ILs with the most hydrophobic cations exhibited the highest affinities for guaiacol, and the distribution coeffs. of both guaiacol and levoglucosan could be correlated to the anion polarities and hence their hydrogen bond interaction abilities with the solutes. Four phosphonium ILs, three imidazolium ILs, and an org. solvent Et acetate (EA) were selected to perform the extn. expts. Trihexyl(tetradecyl)phosphonium dicyanamide (P666,14[N(CN)2]) showed the highest exptl. selectivity of 2159 and almost no levoglucosan was extd. Two conceptual processes were designed for sepn. of guaiacol from water using P666,14[N(CN)2] and EA resp., based on liq.-liq. equil. data for the systems P666,14[N(CN)2] + guaiacol + H2O and EA + guaiacol + H2O, exptl. detd. in this work. The results showed that an EA-based process consisted of more unit operations and required five times more energy (12.42 MJ/kg guaiacol) than an IL-based process (2.15 MJ/kg guaiacol).
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Li, X.; Van Den Bossche, A.; Vander Hoogerstraete, T.; Binnemans, K. Ionic Liquids with Trichloride Anions for Oxidative Dissolution of Metals and Alloys. Chem. Commun. 2018, 54, 475– 478, DOI: 10.1039/C7CC08645H
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Ionic liquids with trichloride anions for oxidative dissolution of metals and alloys
Li, Xiaohua; Van den Bossche, Arne; Vander Hoogerstraete, Tom; Binnemans, Koen
Chemical Communications (Cambridge, United Kingdom) (2018), 54 (5), 475-478CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
Ionic liqs. (ILs) with trichloride anions ([Cl3]-) combined with different cations were synthesized by bringing chlorine gas into contact with the corresponding chloride (Cl-) ILs at room temp. These trichloride ILs safely store chlorine and are useful as oxidizing agents for dissoln. of various metals and alloys under mild conditions.
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Van Den Bossche, A.; De Witte, E.; Dehaen, W.; Binnemans, K. Trihalide Ionic Liquids as Non-Volatile Oxidizing Solvents for Metals. Green Chem. 2018, 20, 3327– 3338, DOI: 10.1039/C8GC01061G
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95
Trihalide ionic liquids as non-volatile oxidizing solvents for metals
Van den Bossche, Arne; De Witte, Elise; Dehaen, Wim; Binnemans, Koen
Green Chemistry (2018), 20 (14), 3327-3338CODEN: GRCHFJ; ISSN:1463-9262. (Royal Society of Chemistry)
Various ionic liqs. contg. a trihalide anion [X3]- (X = Cl, Br or I) were synthesized by addn. of mol. chlorine, bromine or iodine (X2) to a halide ionic liq. precursor, forming the trihalide anion via a Lewis acid-base reaction. All ionic liqs. were characterized by 1H NMR, 13C NMR, 31P NMR, and Raman spectroscopy. Phosphonium trihalide ionic liqs. [PR4][X3] (X = Cl, Br or I) were selected because of their low viscosity, low m.p. and stability towards chlorine. The m.p., viscosity and d. were measured for all ionic liqs. A series of seven trihalide ionic liqs. (with anions ranging from trichloride to triiodide), contg. both single trihalide and mixed trihalide anions, was prepd. for the tributyldecylphosphonium cation. The effect of the trihalide anion on the phys. properties of the phosphonium ionic liqs. was detd. using this series of ionic liqs. Trihalide anions, and polyhalides in general, are strongly oxidizing agents due to their charge deficit with respect to the no. of halogen atoms. This strong oxidizing power has been applied to oxidatively dissolve several metals into tributyldecylphosphonium tribromide [P44410][Br3]. A broad range of metals was tested: Fe, Cu, Sb, Co, Zn, In, Ga, Bi, Ge, Sn, Pd, Au, Rh and Pt. With the exception of Pt and Rh, all the metals dissolved in the ionic liq. The dissoln. of Cu in six different trihalide ionic liqs. was performed to confirm that these trihalide ionic liqs. have similar oxidizing properties to [P44410][Br3]. Due to the negligible vapor pressure of ionic liqs., the entire oxidative dissoln. process proceeded in a non-volatile solvent and without the formation of gases. This work can contribute to the development of safe, solvometallurgical methods for oxidative dissoln. of metals.
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Schmidt, B.; Sonnenberg, K.; Beckers, H.; Steinhauer, S.; Riedel, S. Synthesis and Characterization of Nonclassical Interhalides Based on Bromine Monochloride. Angew. Chem., Int. Ed. 2018, 57, 9141– 9145, DOI: 10.1002/anie.201803705
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Synthesis and Characterization of Nonclassical Interhalides Based on Bromine Monochloride
Schmidt, Benjamin; Sonnenberg, Karsten; Beckers, Helmut; Steinhauer, Simon; Riedel, Sebastian
Angewandte Chemie, International Edition (2018), 57 (29), 9141-9145CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
Due to a more distinct σ-hole, BrCl is able to form stronger halogen bonds than those in polyhalogen anions based on Cl2 and Br2. This stabilization allows the crystallog. characterization of a variety of new polyinterhalides, in which chloride functions as the central ion as shown by the mol. structures of [AsPh4][Cl(BrCl)3] and [CCl(NMe2)2][Cl(BrCl)5]. The solid-state structure of an octahedrally coordinated nonclassical interhalide is reported. The tridecainterhalide monoanion [Cl(BrCl)6]- consists of a central chloride ion, which is coordinated by 6 BrCl mols. in a slightly distorted octahedral structure. All new compds. were characterized by single-crystal XRD, NMR and Raman spectroscopy, as well as quantum-chem. calcns.
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Haller, H.; Riedel, S. Recent Discoveries of Polyhalogen Anions - From Bromine to Fluorine. Z. Anorg. Allg. Chem. 2014, 640, 1281– 1291, DOI: 10.1002/zaac.201400085
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97
Recent Discoveries of Polyhalogen Anions - from Bromine to Fluorine
Haller, Heike; Riedel, Sebastian
Zeitschrift fuer Anorganische und Allgemeine Chemie (2014), 640 (7), 1281-1291CODEN: ZAACAB; ISSN:0044-2313. (Wiley-VCH Verlag GmbH & Co. KGaA)
In this review we discuss the recent discoveries in polyhalide anion chem. with the main focus on polybromide, -chloride, and -fluoride anions. Based on novel synthetic strategies either in ionic liqs. or in neat halogens several new polyhalides of bromine and chlorine were synthesized. Beyond these discoveries the chem. of polyfluoride monoanions is reviewed. Such species were investigated under cryogenic conditions at 4 K in conjunction with quantum-chem. calcns. In addn. to these bonding and structural discussions, an overview of possible applications of such polyhalide anions is provided.
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Sonnenberg, K.; Mann, L.; Redeker, F. A.; Schmidt, B.; Riedel, S. Polyhalogen and Polyinterhalogen Anions from Fluorine to Iodine. Angew. Chem., Int. Ed. 2020, 59, 5464– 5493, DOI: 10.1002/anie.201903197
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98
Polyhalogen and Polyinterhalogen Anions from Fluorine to Iodine
Sonnenberg, Karsten; Mann, Lisa; Redeker, Frenio A.; Schmidt, Benjamin; Riedel, Sebastian
Angewandte Chemie, International Edition (2020), 59 (14), 5464-5493CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
A review. This Review deals with the evolving field of polyhalogen chem., specifically polyhalogen anions (polyhalides). In addn. to a historical outline, current progress in synthetic approaches towards the formation of polyfluorides, polychlorides, polybromides, and polyinterhalides is also illustrated. The structural diversity of polyhalides has substantially increased in the past decade, esp. for polychlorides and polybromides, which are commonly characterized by single-crystal X-ray diffraction, Raman spectroscopy, and quantum-chem. calcns. Polyfluorides have been examd. by sophisticated state-of-the-art quantum-chem. calcns. and investigated spectroscopically in noble gas matrix-isolation expts. under cryogenic conditions at 4 K. The bonding in such polyhalide systems is also discussed. The last Section deals with applications of polyhalides in halogenation reactions and electrochem. as well as their use as reactive ionic liqs., emphasizing the promising future of polyhalogen chem.
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Bortolini, O.; Bottai, M.; Chiappe, C.; Conte, V.; Pieraccini, D. Trihalide-Based Ionic Liquids. Reagent-Solvents for Stereoselective Iodination of Alkenes and Alkynes. Green Chem. 2002, 4, 621– 627, DOI: 10.1039/b209436n
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99
Trihalide-based ionic liquids. Reagent-solvents for stereoselective iodination of alkenes and alkynes
Bortolini, Olga; Bottai, Michele; Chiappe, Cinzia; Conte, Valeria; Pieraccini, Daniela
Green Chemistry (2002), 4 (6), 621-627CODEN: GRCHFJ; ISSN:1463-9262. (Royal Society of Chemistry)
A study of the prepn. of trihalide-based room temp. ionic liqs. (ILs) was made and the structure of trihalide ions was investigated by electrospray ionization mass spectroscopy and NMR. The best procedure consists of mixing equimolar amt. of ICl to [hmim][Cl] and IBr to [bmim][Br] or alternatively Cl2 or Br2 to [emim][I]. Trihalide ILs thus generated were tested as reagent-solvents, or as reagents carrying out the reactions in [bmim][PF6], in iodobromination as well as iodochlorination of alkenes and alkynes. Furthermore, the addn. of ICl and IBr in [bmim][PF6] was investigated. Yields of vic-iodochloro or iodobromo adducts from very good to almost quant. are obsd. for all the substrates examd.
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Chiappe, C.; Leandri, E.; Pieraccini, D. Highly Efficient Bromination of Aromatic Compounds Using 3-Methylimidazolium Tribromide as Reagent/Solvent. Chem. Commun. 2004, 2536– 2537, DOI: 10.1039/b410796a
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100
Highly efficient bromination of aromatic compounds using 3-methylimidazolium tribromide as reagent/solvent
Chiappe, Cinzia; Leandri, Elsa; Pieraccini, Daniela
Chemical Communications (Cambridge, United Kingdom) (2004), (22), 2536-2537CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
3-Methylimidazolium tribromide proves to be an alternative highly efficient reagent/solvent for the halogenation of non-activated arom. compds.
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Cristiano, R.; Ma, K.; Pottanat, G.; Weiss, R. G. Tetraalkylphosphonium Trihalides. Room Temperature Ionic Liquids As Halogenation Reagents. J. Org. Chem. 2009, 74, 9027– 9033, DOI: 10.1021/jo901735h
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101
Tetraalkylphosphonium Trihalides: Room Temperature Ionic Liquids as Halogenation Reagents
Cristiano, Rodrigo; Ma, Kefeng; Pottanat, George; Weiss, Richard G.
Journal of Organic Chemistry (2009), 74 (23), 9027-9033CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
Six room temp. ionic liqs. (RTILs) comprised of a tetraalkylphosphonium cation (tridecylmethyphosphonium or trihexyltetradecylphosphonium) and a trihalide anion (Br3-, BrCl2-, or ClBr2-) have been prepd. and characterized via halogenation of the corresponding tetraalkylphosphonium monohalides. Their ability to effect halogenation reactions with a variety of substrates has been explored. In general, halogenation reactions of alkenes proceed with high yields and stereo- and regioselectivities, whether performed in the absence or presence of a solvent (chloroform). Reactions of an alkyne and electrophilic substitution on an electron rich arom. ring have been investigated as well. The facile prepn. of the salts, their ease of handling, and the simplicity of product isolation should make these RTILs useful addns. to the repertoire of halogenation reagents and the reagents of choice for specific transformations.
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102
Rogers, R. D.; Holbrey, J. Ionic Liquid Solvents of Perhalide Type for Metals and Metal Compounds. WO 2010116167A1, 2010.
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There is no corresponding record for this reference.
103
Van Den Bossche, A.; Vereycken, W.; Vander Hoogerstraete, T.; Dehaen, W.; Binnemans, K. Recovery of Gallium, Indium, and Arsenic from Semiconductors Using Tribromide Ionic Liquids. ACS Sustainable Chem. Eng. 2019, 7, 14451– 14459, DOI: 10.1021/acssuschemeng.9b01724
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103
Recovery of Gallium, Indium, and Arsenic from Semiconductors Using Tribromide Ionic Liquids
Van den Bossche, Arne; Vereycken, Willem; Vander Hoogerstraete, Tom; Dehaen, Wim; Binnemans, Koen
ACS Sustainable Chemistry & Engineering (2019), 7 (17), 14451-14459CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
Leaching of semiconductors (GaN, GaAs, and InAs) and light-emitting diodes (LEDs) in a nonvolatile tribromide ionic liq., and the selective recovery of gallium, indium, and arsenic from this ionic liq. were investigated. To prevent the formation of the highly toxic arsine (AsH3), usually formed when leaching metal arsenides with acids, the hydrophobic trihalide ionic liq. tributyldecylphosphonium tribromide [P44410][Br3] was used to oxidatively leach the semiconductors, avoiding arsine formation. After leaching, a selective stripping procedure was applied to remove and recover arsenic, gallium, and indium. Arsenic and gallium could be stripped using NaBr solns. and pure water, resp., while indium was removed from the ionic liq. phase via pptn. stripping with a NaOH soln. A mechanistic study was performed to explain this difference in stripping behavior. A flowsheet was proposed and, finally, the procedure was applied to real LEDs.
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May, B.; Lexow, M.; Taccardi, N.; Steinrück, H. P.; Maier, F. Reactions of a Polyhalide Ionic Liquid with Copper, Silver, and Gold. ChemistryOpen 2019, 8, 15– 22, DOI: 10.1002/open.201800149
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104
Reactions of a Polyhalide Ionic Liquid with Copper, Silver, and Gold
May, Benjamin; Lexow, Matthias; Taccardi, Nicola; Steinrueck, Hans-Peter; Maier, Florian
ChemistryOpen (2019), 8 (1), 15-22CODEN: CHOPCK; ISSN:2191-1363. (Wiley-VCH Verlag GmbH & Co. KGaA)
The reactions of copper, silver, and gold with the imidazolium-based polyhalide ionic liq. (IL) [C6C1Im][Br2I] were investigated by using XPS, wt.-loss measurements, and gas-phase mass spectrometry. All three Group 11 metals are strongly corroded by the IL at moderate temps. to give a very high content of dissolved CuI, AgI, and AuI species. The IL-metal solns. are stable against contact with water and air. The replacement of imidazolium with inorg. sodium cations decreased metal corrosion rates by orders of magnitude. Our results clearly indicate metal oxidn. by iodide from dibromoiodide anions to form mol. iodine and anionic [Br-MI-Br]- (M=Cu, Ag, Au) complexes stabilized by imidazolium counterions. From expts. with a trihalide IL with imidazolium methylated at the 2-position, we ruled out the formation of imidazole-carbene as a cause of the obsd. corrosion. In contrast to Group 11 metals, molybdenum is inert against the trihalide IL, which is attributed to surface passivation.
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Schmidt, B.; Schröder, B.; Sonnenberg, K.; Steinhauer, S.; Riedel, S. From Polyhalides to Polypseudohalides: Chemistry Based on Cyanogen Bromide. Angew. Chem., Int. Ed. 2019, 58, 10340– 10344, DOI: 10.1002/anie.201903539
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From Polyhalides to Polypseudohalides: Chemistry Based on Cyanogen Bromide
Schmidt, Benjamin; Schroeder, Benjamin; Sonnenberg, Karsten; Steinhauer, Simon; Riedel, Sebastian
Angewandte Chemie, International Edition (2019), 58 (30), 10340-10344CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
Pseudohalogens are defined as mol. entities that resemble the halogens in their chem. While the understanding of polyhalogen chem. has increased over the last years, research on polypseudohalogen compds. is lacking. The pseudohalogen BrCN possesses a highly pronounced σ-hole at the bromine side of the mol., inducing strong halogen bonding. This allows the synthesis and characterization of new polypseudohalogen anions, as shown by the single-crystal x-ray diffraction of [PNP][Br(BrCN)] and [PNP][Br(BrCN)3]. Both the nearly linear anion [Br(BrCN)]- and the distorted pyramidal anion [Br(BrCN)3]- were characterized by Raman spectroscopy and quantum-chem. calcns. The behavior of the polypseudohalogen compds. in soln. and as room-temp. ionic liqs. (RT-ILs) using the [NBu4]+ cation was studied by 13C and 15N NMR spectroscopy. These types of ILs are capable of dissolving elemental gold and offer themselves as promising compds. in metal recycling.
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Whitehead, J. A.; Lawrance, G. A.; McCluskey, A. Green” Leaching: Recyclable and Selective Leaching of Gold-Bearing Ore in an Ionic Liquid. Green Chem. 2004, 6, 313– 315, DOI: 10.1039/B406148A
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'Green' leaching: recyclable and selective leaching of gold-bearing ore in an ionic liquid
Whitehead, Jacqueline A.; Lawrance, Geoffrey A.; McCluskey, Adam
Green Chemistry (2004), 6 (7), 313-315CODEN: GRCHFJ; ISSN:1463-9262. (Royal Society of Chemistry)
The recovery of gold and silver from ore in an ionic liq. is reported for the first time. The 1-butyl-3-methyl-imidazolium hydrogen sulfate ionic liq. (bmim+HSO4-) was employed, with iron(III) sulfate oxidant and thiourea added. Selective extn. of gold (≥85%) and silver (≥60%) from powd. ore (of dominantly chalcopyrite/pyrite/pyrrhotite/sphalerite mineralogy) was achieved at room temp. in 50 h, with other lower-value metals present in the ore (Cu, Zn, Pb, Fe) extd. to only low percentages. Gold extn. was similar to that achieved in aq. H2SO4/thiourea/Fe2(SO4)3, and silver extn. was significantly better. Moreover, the ionic liq. can be recycled following selective stripping of gold and silver on activated charcoal, with reuse in at least four successive treatments leading to neither ionic liq. degrdn. nor any loss in extn. efficiency.
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Whitehead, J. A.; Zhang, J.; McCluskey, A.; Lawrance, G. A. Comparative Leaching of a Sulfidic Gold Ore in Ionic Liquid and Aqueous Acid with Thiourea and Halides Using Fe(III) or HSO₅⁻ Oxidant. Hydrometallurgy 2009, 98, 276– 280, DOI: 10.1016/j.hydromet.2009.05.012
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Comparative leaching of a sulfidic gold ore in ionic liquid and aqueous acid with thiourea and halides using Fe(III) or HSO5- oxidant
Whitehead, J. A.; Zhang, J.; McCluskey, A.; Lawrance, G. A.
Hydrometallurgy (2009), 98 (3-4), 276-280CODEN: HYDRDA; ISSN:0304-386X. (Elsevier B.V.)
The leaching of gold, silver and base metals from a sulfidic gold ore in the presence of an oxidant (peroxomonosulfate (HSO5-) or iron(III)) and leaching agent (thiourea, chloride, bromide or iodide) is compared in 1-butyl-3-methylimidazolium hydrogen sulfate (bmimHSO4) and chloride (bmimCl) ionic liqs., as well as in aq. satd. K2SO4 as the solvent medium. Over 85% of gold and silver was recovered in the presence of HSO5-/ thiourea at 25-50° in both ionic liqs., with silver recovery significantly enhanced compared with that from aq. sulfate medium. The leaching efficiency with HSO5- was similar to that with Fe(III) as oxidant in bmimHSO4 and was far superior in bmimCl. With HSO5-/halide ion (Cl-, Br-, I-) as leaching agent, gold and silver recovery in the ionic liqs. or satd. aq. K2SO4 improved from Cl- to Br- to I-, but only I- gave a high recovery in the bmimCl ionic liq. due to the particular stability of the iodo complex anion in this medium. However, recovery was significantly higher than that in an aq. medium. Negligible recovery of base metals occurred in the ionic liq. medium, which makes it highly selective for Au and Ag. Concn. dependence studies with respect to halide and oxidant have defined optimum conditions for gold and silver recovery.
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Whitehead, J. A.; Zhang, J.; Pereira, N.; McCluskey, A.; Lawrance, G. A. Application of 1-Alkyl-3-Methyl-Imidazolium Ionic Liquids in the Oxidative Leaching of Sulphidic Copper, Gold and Silver Ores. Hydrometallurgy 2007, 88, 109– 120, DOI: 10.1016/j.hydromet.2007.03.009
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Application of 1-alkyl-3-methyl-imidazolium ionic liquids in the oxidative leaching of sulfidic copper, gold and silver ores
Whitehead, J. A.; Zhang, J.; Pereira, N.; McCluskey, A.; Lawrance, G. A.
Hydrometallurgy (2007), 88 (1-4), 109-120CODEN: HYDRDA; ISSN:0304-386X. (Elsevier B.V.)
The application of 1-butyl-3-methyl-imidazolium hydrogen sulfate ionic liq. and close analogs is described as a solvent medium (either as a neat liq. and or as aq. mixts.) for the leaching of gold, silver, copper and base metals from sulfidic ores by using mainly thiourea in the presence of iron(III) as oxidant. Initially pyrite and chalcopyrite leaching were studied. Copper extn. from chalcopyrite was much more efficient than iron extn. in the ionic liq. medium at 70°by increasing from 55 to 87% as the ionic liq. compn. increased from 10% wt./wt. in water to 100%. This compared with only 23% Cu extn. by 1 M H2SO4 under equiv. conditions. Gold recovery was >85% from both a synthetic oxidic ore and natural sulfidic ore in the presence of iron(III)/thiourea at 20-50° in the ionic liq. Silver recovery from a natural sulfidic ore at >60% was significantly higher compared with that leached with an aq. acid medium at <10%. The effect of varying the alkyl chain length in the (n-alkyl) methyl-imidazolium cation and of varying the anion in the ionic liqs. (Cl-, CH3SO3-, N(CN)2-, HSO4-) on metal ion recovery from the ores was also examd. and showed that the ionic liq. used was the most effective solvent medium. Oxygen soly. in several ionic liqs. is also reported and is similar to that of oxygen in water. Eight other S-contg. leaching agents, in addn. to thiourea, were explored for metal ion extn. with iron(III) as oxidant in the ionic liq. system. Apart from thiourea, only 2-mercaptothiazoline showed promising behavior.
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Bentley, C. L.; Bond, A. M.; Hollenkamp, A. F.; Mahon, P. J.; Zhang, J. Unexpected Complexity in the Electro-Oxidation of Iodide on Gold in the Ionic Liquid 1-Ethyl-3-Methylimidazolium Bis(Trifluoromethanesulfonyl)Imide. Anal. Chem. 2013, 85, 11319– 11325, DOI: 10.1021/ac402150y
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Unexpected Complexity in the Electro-Oxidation of Iodide on Gold in the Ionic Liquid 1-Ethyl-3-methyl-imidazolium bis(trifluoro-methane-sulfonyl)imide
Bentley, Cameron L.; Bond, Alan M.; Hollenkamp, Anthony F.; Mahon, Peter J.; Zhang, Jie
Analytical Chemistry (Washington, DC, United States) (2013), 85 (23), 11319-11325CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
The electrooxidn. of iodide on a Au electrode in the room temp. ionic liq. 1-ethyl-3-methyl-imidazolium bis-(trifluoro-methane-sulfonyl)-imide was studied using transient cyclic voltammetry, linear-sweep semi-integral voltammetry, an electrochem. quartz crystal microbalance technique, and coulometry/electrogravimetry. Two oxidn. processes are obsd., with an electron stoichiometry of 1:1, compared with the known 2:1 electron stoichiometry obsd. on other commonly used electrode materials, such as Pt, glassy C, and B-doped diamond, under identical conditions. Detailed mechanistic information, obtained in situ using an electrochem. quartz crystal microbalance, reveals that this unusual observation can be attributed to the dissoln. of the Au electrode in the presence of iodide. Coulometric/electrogravimetric anal. suggests that the oxidn. state of the sol. Au species is +1 and that diiodoaurate, [AuI2]-, is the likely intermediate. A proportionally smaller amt. of triiodide intermediate is also detected by UV-visible spectroscopy. On this basis, probably iodide oxidn. on Au occurs via two parallel pathways: predominantly via a diiodoaurate intermediate 2I- + Au $Equil.$ [AuI2]- + e- and [AuI2]- $Equil.$ I2 + Au + e- and to a lesser extent via a triiodide intermediate 3I- $Equil.$ I3- + 2e- and I3- $Equil.$ 3/2I2 + e-. This proposed mechanism was further supported by voltammetric studies with an authentic sample of the anionic [AuI2]- complex.
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Balva, M.; Legeai, S.; Leclerc, N.; Billy, E.; Meux, E. Environmentally Friendly Recycling of Fuel-Cell Membrane Electrode Assemblies by Using Ionic Liquids. ChemSusChem 2017, 10, 2922– 2935, DOI: 10.1002/cssc.201700456
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Environmentally Friendly Recycling of Fuel-Cell Membrane Electrode Assemblies by Using Ionic Liquids
Balva, Maxime; Legeai, Sophie; Leclerc, Nathalie; Billy, Emmanuel; Meux, Eric
ChemSusChem (2017), 10 (14), 2922-2935CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
The Pt nanoparticles used as the catalyst in proton exchange membrane fuel cells (PEMFCs) represent ∼46% of the total price of the cells for a large-scale prodn., and this is one of the barriers to their commercialization. Therefore, the recycling of the Pt catalyst could be the best alternative to limit the prodn. costs of PEMFCs. The usual recovery routes for spent catalysts contg. Pt are pyro-hydrometallurgical processes in which a calcination step is followed by aqua regia treatment, and these processes generate fumes and NOx emissions, resp. The electrochem. recovery route proposed here is more environmentally friendly, performed under soft temp. conditions, and does not result in any gas emissions. It consists of the coupling of the electrochem. leaching of Pt in chloride-based ionic liqs. (ILs), followed by its electrodeposition. The leaching of Pt was studied in pure ILs and in ionic-liq. melts at different temps. and with different chloride contents. Through the modulation of the compn. of the ionic-liq. melts, it is possible to leach and electrodeposit the Pt from fuel-cell electrodes in a single-cell process under an inert or ambient atm.
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Deferm, C.; Hulsegge, J.; Möller, C.; Thijs, B. Electrochemical Dissolution of Metallic Platinum in Ionic Liquids. J. Appl. Electrochem. 2013, 43, 789– 796, DOI: 10.1007/s10800-013-0541-6
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Electrochemical dissolution of metallic platinum in ionic liquids
Deferm, Clio; Hulsegge, Jaco; Moller, Claudia; Thijs, Ben
Journal of Applied Electrochemistry (2013), 43 (8), 789-796CODEN: JAELBJ; ISSN:0021-891X. (Springer)
The electrochem. dissoln. of Pt in several ionic liqs. (IL's) was studied. Different IL's were tested assessing their potential to dissolve Pt. Dissoln. rate and current efficiency were evaluated. The main focus was on Cl contg. IL's: 1st generation, eutectic based IL's and 2nd generation IL's with discrete anions. Pt dissoln. only occurred in type 1 eutectic-based IL's with a max. dissoln. rate of 192.2 g m-2 h-1 and a max. current efficiency of 99% for the ZnCl2-1-ethyl-3-methylimidazolium chloride IL, and 9.090 g m-2 h-1 and 96% for the 1:1 ZnCl2-choline chloride ionic liq. The dissoln. occurred via the formation of [PtClx]y- complexes. To form these complexes, addn. of a metal chloride was necessary. Also, an IL with an electrochem. window of 1.5 V, preferably 2.0 V is required to achieve Pt dissoln. The added metal salt needed to have a higher decompn. potential than 1.5 V or should be a Pt salt.
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Smith, E. L.; Abbott, A. P.; Ryder, K. S. Deep Eutectic Solvents (DESs) and Their Applications. Chem. Rev. 2014, 114, 11060– 11082, DOI: 10.1021/cr300162p
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Deep Eutectic Solvents (DESs) and Their Applications
Smith, Emma L.; Abbott, Andrew P.; Ryder, Karl S.
Chemical Reviews (Washington, DC, United States) (2014), 114 (21), 11060-11082CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
This article describes the phys. and chem. properties of deep eutectic solvents (DESs) and ionic liq. (ILs), and how their applications differ. DESs are now widely acknowledged as a new class of IL analogs because they share many characteristics and properties with ILs. The terms DES and IL have been used interchangeably in the literature, though it is necessary to point out that these are actually two different types of solvent. DESs are systems formed from a eutectic mixt. of Lewis or Bronsted acids and bases which can contain a variety of anionic and/or cationic species; in contrast, ILs are formed from systems composed primarily of one type of discrete anion and cation.
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Jenkin, G. R. T.; Al-Bassam, A. Z. M.; Harris, R. C.; Abbott, A. P.; Smith, D. J.; Holwell, D. A.; Chapman, R. J.; Stanley, C. J. The Application of Deep Eutectic Solvent Ionic Liquids for Environmentally-Friendly Dissolution and Recovery of Precious Metals. Miner. Eng. 2016, 87, 18– 24, DOI: 10.1016/j.mineng.2015.09.026
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The application of deep eutectic solvent ionic liquids for environmentally-friendly dissolution and recovery of precious metals
Jenkin, Gawen R. T.; Al-Bassam, Ahmed Z. M.; Harris, Robert C.; Abbott, Andrew P.; Smith, Daniel J.; Holwell, David A.; Chapman, Robert J.; Stanley, Christopher J.
Minerals Engineering (2016), 87 (), 18-24CODEN: MENGEB; ISSN:0892-6875. (Elsevier Ltd.)
The processing of ore by hydrometallurgy or pyrometallurgy typically has a high energy demand, and assocd. release of carbon dioxide. Thus there is a need to develop more energy-efficient and environmentally-compatible processes. This article demonstrates that deep eutectic solvent (DES) ionic liqs. provide one such method since they can be used to selectively dissolve and recover native gold and tellurium, sulfides and tellurides. Ionic liqs. are anhyd. salts that are liq. at low temp. They are powerful solvents and electrolytes with potential for high selectivity in both dissoln. and recovery. Deep eutectic solvents are a form of ionic liq. that are mixts. of salts such as choline chloride with hydrogen-bond donors such as urea. DESs are environmentally benign, yet chem. stable and, furthermore, the components are already produced in large quantities at comparable costs to conventional reagents. Electrum, galena and chalcopyrite, as well as tellurobismuthite (Bi2Te3), were sol. in DES through an oxidative leach at 45-50°C. Leaching rates detd. by a novel technique employing an optical profiler were very favorable in comparison to the current industrial process of cyanidation. Pyrite was notably insol. by an oxidative leach. However, pyrite, and indeed any other sulfide, could be selectively dissolved by electrolysis in a DES, thus suggesting a protocol whereby target inclusions could be liberated by electrolysis and then dissolved by subsequent oxidn. Ionometallurgy could thus offer a new set of environmentally-benign process for metallurgy.
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Abbott, A. P.; Capper, G.; Swain, B. G.; Wheeler, D. A. Electropolishing of Stainless Steel in an Ionic Liquid. Trans. Inst. Met. Finish. 2005, 83, 51– 53, DOI: 10.1179/002029605X17657
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Electropolishing of stainless steel in an ionic liquid
Abbott, A. P.; Capper, G.; Swain, B. G.; Wheeler, D. A.
Transactions of the Institute of Metal Finishing (2005), 83 (1), 51-53CODEN: TIMFA2; ISSN:0020-2967. (Maney Publishing)
Efficient electropolishing of stainless steel is demonstrated in an ionic liq. produced from ethylene glycol and choline chloride (HOC2H4N(CH3)3+Cl-). The metal dissolves without prior passivation and no gassing is obsd. at the anode surface. No dealloying of the substrate is obsd. and no changes in the polish quality are obsd. as the ionic liq. ages.
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Abbott, A. P.; Frisch, G.; Hartley, J.; Karim, W. O.; Ryder, K. S. Anodic Dissolution of Metals in Ionic Liquids. Prog. Nat. Sci. 2015, 25, 595– 602, DOI: 10.1016/j.pnsc.2015.11.005
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Anodic dissolution of metals in ionic liquids
Abbott, Andrew P.; Frisch, Gero; Hartley, Jennifer; Karim, Wrya O.; Ryder, Karl S.
Progress in Natural Science: Materials International (2015), 25 (6), 595-602CODEN: PNSMBB ISSN:. (Elsevier B.V.)
The anodic dissoln. of metals is an important topic for battery design, material finishing and metal digestion. Ionic liqs. are being used in all of these areas but the research on the anodic dissoln. is relatively few in these media. This study investigates the behavior of 9 metals in an ionic liq. [C4mim][Cl] and a deep eutectic solvent, Ethaline, which is a 1:2 mol ratio mixt. of choline chloride and ethylene glycol. It is shown that for the majority of metals studied a quasi-passivation of the metal surface occurs, primarily due to the formation of insol. films on the electrode surface. The behavior of most metals is different in [C4mim][Cl] to that in Ethaline due in part to the differences in viscosity. The formation of passivating salt films can be decreased with stirring or by increasing the electrolyte temp., thereby increasing ligand transport to the electrode surface.
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Smith, E. L.; Fullarton, C.; Harris, R. C.; Saleem, S.; Abbott, A. P.; Ryder, K. S. Metal Finishing with Ionic Liquids: Scale-up and Pilot Plants from IONMET Consortium. Trans. Inst. Met. Finish. 2010, 88, 285– 291, DOI: 10.1179/174591910X12856686485734
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Metal finishing with ionic liquids: scale-up and pilot plants from IONMET consortium
Smith, E. L.; Fullarton, C.; Harris, R. C.; Saleem, S.; Abbott, A. P.; Ryder, K. S.
Transactions of the Institute of Metal Finishing (2010), 88 (6), 285-291CODEN: TIMFA2; ISSN:0020-2967. (Maney Publishing)
A review on the successful scale-up of five ionic liq. processes by the IONMET consortium is given. Metal finishing demonstrator technologies were developed based on ionic liq. systems for the electropolishing of stainless steels and other alloys, galvanic immersion (dip coating) deposition of Ag for finishing of printed circuit boards as well as electrolytic deposition of hard chrome coatings, Al coatings and barrel plating of Zn-Sn alloys. Some of these systems can be considered as 'drop-in' replacement technologies for existing aq. processes that currently require strong inorg. acids and highly toxic reagents.
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Mortier, T.; Persoons, A.; Verbiest, T. Oxidation of Solid Gold in Chloroform Solutions of Cetyltrimethylammonium Bromide. Inorg. Chem. Commun. 2005, 8, 1075– 1077, DOI: 10.1016/j.inoche.2005.08.015
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Oxidation of solid gold in chloroform solutions of cetyltrimethylammonium bromide
Mortier, Tom; Persoons, Andre; Verbiest, Thierry
Inorganic Chemistry Communications (2005), 8 (12), 1075-1077CODEN: ICCOFP; ISSN:1387-7003. (Elsevier B.V.)
Oxidn. of solid Au was studied in CHCl3 solns. of cetyltrimethylammonium bromide (CTAB). Upon sonication, solid Au is oxidized and cetyltrimethylammonium tetrabromo aurate is formed. The Br- ions act as a nucleophile that lowers the redn. potential of Au and mol. O from the air acts as an oxidant. Addn. of hydrazine to the sonicated soln. gives Au nanoparticles dispersed in CHCl3.
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Barnartt, S.; Charles, R. G.; Littau, L. W. Reactions of Liquid Acetylacetone with Metal Surfaces. J. Phys. Chem. 1958, 62, 763– 766, DOI: 10.1021/j150564a036
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Reactions of liquid acetylacetone with metal surfaces
Barnartt, Sidney; Charles, Robert G.; Littau, Laurence W.
Journal of Physical Chemistry (1958), 62 (), 763-6CODEN: JPCHAX; ISSN:0022-3654.
Pb, Mn, Zn, Mg, Cd, Fe, Cu, Co, In, and Sn react with acetylacetone plus O at a measurable rate. Ti, Zr, V, Nb, Ta, Cr, Mo, W, Ni, Al, Si, Ge, and Sb show a reaction rate less than 2 γ/sq. cm./hr. Mn, Fe, and Co react in the presence of O to form the trivalent chelate. Mg, Mn, Zn, and In react at 27° in a N atm. with the evolution of H.
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Räisänen, M. T.; Kemell, M.; Leskelä, M.; Repo, T. Oxidation of Elemental Gold in Alcohol Solutions. Inorg. Chem. 2007, 46, 3251– 3256, DOI: 10.1021/ic0624468
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Oxidation of elemental gold in alcohol solutions
Raisanen Minna T; Kemell Marianna; Leskela Markku; Repo Timo
Inorganic chemistry (2007), 46 (8), 3251-6 ISSN:0020-1669.
Gold is designated as the noblest metal because of its chemical inertness. It is known to dissolve in cyanide solutions in the presence of air or H2O2 or in halogen-containing solutions, aqua regia being the most famous example. Herein, we report a unique thiol, especially 4-pyridinethiol (4-PS), assisted dissolution of Au in alcohol solutions. Although dissolution was found to be very selective for pyridinethiols, such a phenomenon is astonishing since thiols are commonly used as etch resists for Au and even 4-PS is extensively used as a surface modifier for Au. To gain further understanding of the dissolution process, the influence of the reaction conditions was extensively studied. On the basis of the obtained results, a mechanism for the dissolution reaction is proposed. Fascinatingly, by tuning of the reaction conditions, this phenomenon can be applied in selective preparation of self-supporting nanometer-thick Au foils.
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Räisänen, M.; Heliövaara, E.; Al-Qaisi, F.; Muuronen, M.; Eronen, A.; Liljeqvist, H.; Nieger, M.; Kemell, M.; Moslova, K.; Hämäläinen, J.; Lagerblom, K.; Repo, T. Pyridinethiol-Assisted Dissolution of Elemental Gold in Organic Solutions. Angew. Chem., Int. Ed. 2018, 57, 17104– 17109, DOI: 10.1002/anie.201810447
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120
Pyridinethiol-Assisted Dissolution of Elemental Gold in Organic Solutions
Raisanen Minna; Heliovaara Eeva; Al-Qaisi Feda'a; Eronen Aleksi; Liljeqvist Henri; Nieger Martin; Kemell Marianna; Moslova Karina; Hamalainen Jani; Lagerblom Kalle; Repo Timo; Raisanen Minna; Al-Qaisi Feda'a; Muuronen Mikko; Muuronen Mikko
Angewandte Chemie (International ed. in English) (2018), 57 (52), 17104-17109 ISSN:.
Dissolution of elemental gold in organic solutions is a contemporary approach to lower the environmental burden associated with gold recycling. Herein, we describe fundamental studies on a highly efficient method for the dissolution of elemental Au that is based on DMF solutions containing pyridine-4-thiol (4-PSH) as a reactive ligand and hydrogen peroxide as an oxidant. Dissolution of Au proceeds through several elementary steps: isomerization of 4-PSH to pyridine-4-thione (4-PS), coordination with Au(0) , and then oxidation of the Au(0) thione species to Au(I) simultaneously with oxidation of free pyridine thione to elemental sulfur and further to sulfuric acid. The final dissolution product is a Au(I) complex bearing two 4-PS ligands and SO4(2-) as a counterion. The ligand is crucial as it assists the oxidation process and stabilizes and solubilizes the formed Au cations.
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Antoniotti, S.; Duñach, E. Facile Preparation of Metallic Triflates and Triflimidates by Oxidative Dissolution of Metal Powders. Chem. Commun. 2008, 993– 995, DOI: 10.1039/b717689a
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Facile preparation of metallic triflates and triflimidates by oxidative dissolution of metal powders
Antoniotti, Sylvain; Dunach, Elisabet
Chemical Communications (Cambridge, United Kingdom) (2008), (8), 993-995CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
Various metallic triflates and triflimidates were prepd. by the straightforward oxidative dissoln. of the corresponding metal powder in DMSO under an atm. pressure of O2 in the presence of stoichiometric amts. of triflic or triflimidic acid. Sn(NTf2)4 7.9DMSO catalyzed the cycloisomerization of di-Et diprenylmalonate to its cyclohexane deriv.
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Legrave, N.; Couhert, A.; Olivero, S.; Desmurs, J. R.; Duñach, E. Efficient Preparation of Anhydrous Metallic Triflates and Triflimides under Ultrasonic Activation. Eur. J. Org. Chem. 2012, 2012, 901– 904, DOI: 10.1002/ejoc.201101686
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Efficient Preparation of Anhydrous Metallic Triflates and Triflimides under Ultrasonic Activation
Legrave, Nathalie; Couhert, Audrey; Olivero, Sandra; Desmurs, Jean-Roger; Dunach, Elisabet
European Journal of Organic Chemistry (2012), 2012 (5), 901-904CODEN: EJOCFK; ISSN:1099-0690. (Wiley-VCH Verlag GmbH & Co. KGaA)
Several metallic triflates and triflimides, among them anhyd. salts, were prepd. in high yields under ultrasonic activation from the corresponding metal powders and stoichiometric amts. of triflic or triflimidic acid in different solvents. Different InIII and BiIII salts were tested as catalysts in hydrothiolation of olefins and in hydroarylation processes, resp.
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Panteleev, S. V.; Maslennikov, S. V.; Egorochkin, A. N.; Vakulenko, V. Y. Solvent Effect on Metal Oxidation Rates in Aprotic Media. Russ. J. Gen. Chem. 2007, 77, 1004– 1007, DOI: 10.1134/S1070363207060084
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Solvent effect on metal oxidation rates in aprotic media
Panteleev, S. V.; Maslennikov, S. V.; Egorochkin, A. N.; Vakulenko, V. Yu.
Russian Journal of General Chemistry (2007), 77 (6), 1004-1007CODEN: RJGCEK; ISSN:1070-3632. (Pleiades Publishing, Ltd.)
A correlation between the rates of oxidn. of metals with organometallic chlorides in aprotic media and the physicochem. properties of the solvents was established. An equation fitting the exptl. data for ten reaction series was suggested. The kinetic parameters of oxidn. of cadmium with diphenyl-bismuth chloride in aprotic media, calcd. with the correlation equations, coincide with the exptl. data.
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Petrusenko, S. R.; Sieler, J.; Kokozay, V. N. Direct Synthesis of Zinc and Nickel(II) Complexes with 1,4-Diazabicyclo[2.2.2]Octane. Z. Naturforsch., B: J. Chem. Sci. 1997, 52, 331– 336, DOI: 10.1515/znb-1997-0305
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Kokozay, V. N.; Vassilyeva, O. Y.; Weinberger, P.; Wasinger, M.; Linert, W. Direct Synthesis of Polynuclear Complexes. Rev. Inorg. Chem. 2000, 20, 255– 282, DOI: 10.1515/REVIC.2000.20.4.255
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Direct synthesis of polynuclear complexes
Kokozay, Vladimir N.; Vassilyeva, Olga Yu.; Weinberger, Peter; Wasinger, Michaela; Linert, Wolfgang
Reviews in Inorganic Chemistry (2000), 20 (4), 255-282CODEN: RICHD7; ISSN:0193-4929. (Freund Publishing House Ltd.)
A review with 40 refs. Conventional synthesis of metal complexes normally involves a metal salt as a starting material. Direct synthesis employs zerovalent metal and is expected to yield a great variety of novel polynuclear structures and properties. Data on direct synthesis of polynuclear and mixed-valent compds. from zerovalent metals in nonaq. solns. of ammonium/alkylammonium salts are described. The prepn. of mixed-metal Cu/M (Pb, Co, Ni, Zn) complexes synthesized using zerovalent Cu as a starting material is presented. Main rules of the formation of mixed-metal complexes are discussed with particular interest focused on the structural characterization.
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Abbott, J. K. C.; Dougan, B. A.; Xue, Z. L. Synthesis of Organometallic Compounds. In Modern Inorganic Synthetic Chemistry; Xu, R., Pang, W., Huo, Q., Eds.; Elsevier: Amsterdam, 2011; pp 269– 293.
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127
Chakravorti, M. C.; Subrahmanyam, G. V. B. Electrosynthesis of Coordination Compounds by the Dissolution of Sacrificial Metal Anodes. Coord. Chem. Rev. 1994, 135–136, 65– 92, DOI: 10.1016/0010-8545(94)80065-0
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Electrosynthesis of Coordination Compounds by the Dissolution of Sacrificial Metal Anodes
Chakravorti, M. C.; Subrahmanyam, Gampa V. B.
Coordination Chemistry Reviews (1994), 135/136 (), 65-92CODEN: CCHRAM; ISSN:0010-8545. (Elsevier)
A review with 144 refs. is given on electrosynthesis of different kinds of coordination compds. by the dissoln. of sacrificial anodes in aq. and nonaq. media.
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Chygorin, E. M.; Makhankova, V. G.; Ischenko, M. V.; Kokozay, V. N.; Zubatyuk, R. I.; Shishkin, O. V.; Jezierska, J. Direct Synthesis and Properties of Monomeric and Dimeric Mn III-Salen Complexes Tuned by Tetrahalocadmate Anions. Inorg. Chem. Commun. 2012, 20, 282– 285, DOI: 10.1016/j.inoche.2012.03.029
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Direct synthesis and properties of monomeric and dimeric MnIII-salen complexes tuned by tetrahalocadmate anions
Chygorin, Eduard M.; Makhankova, Valeriya G.; Ischenko, Mykola V.; Kokozay, Vladimir N.; Zubatyuk, Roman I.; Shishkin, Oleg V.; Jezierska, Julia
Inorganic Chemistry Communications (2012), 20 (), 282-285CODEN: ICCOFP; ISSN:1387-7003. (Elsevier B.V.)
Two [Mn(salen)(DMF)2]3[Mn(salen)(DMF)(H2O)][CdCl4]2·H2O (1) and {[Mn(salen)(MeOH)]2}[Mn(salen)(MeOH)2]2[CdI4]2 (2) were synthesized via interaction of Mn metal and Cd halide with in situ generated salen ligand (salen = N,N'-ethylene-bis-salicylideneaminato) in nonaq. (DMF, MeOH) solns. X-ray structure anal. reveals that in solid state 1 contains mononuclear MnIII-salen species, while in 2 both monomeric and out-of-plane dimeric MnIII-salen complexes are present. Also, in 2 the monomeric units are linked by hydrogen bonds, forming other dimers. Equil. between monomeric and dimeric units in solns. of 1 and 2 was found by ESI mass-spectrometry. The magnetic measurements of 2 demonstrated antiferromagnetic interactions between MnIII centers.
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Buchikhin, E. P.; Kuznetsov, A. Y.; Vidanov, V. L.; Shatalov, V. V. Reaction of Metallic Uranium with NO₂ in TBP. Radiochemistry 2006, 48, 459– 461, DOI: 10.1134/S1066362206050080
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Reaction of metallic uranium with NO2 in TBP
Buchikhin, E. P.; Kuznetsov, A. Yu.; Vidanov, V. L.; Shatalov, V. V.
Radiochemistry (New York, NY, United States) (2006), 48 (5), 459-461CODEN: RDIOEO; ISSN:1066-3622. (Pleiades Publishing, Inc.)
Low-temp. nonaq. nitration of metallic uranium in the system TBP tetrachloroethylene-NO2 is studied. Dissoln. of U in a dipolar aprotic solvent (TBP, DMF, acetonitrile, nitromethane, DMSO, diethylformamide) proceeds with the formation of U(VI) compds. The activation energy of the process is estd. at 48.2 kJ mol-1, and the partial order of the reaction with respect to NO2 is 1. The effects of the TBP concn. and water addn. on the nitration are examd. In the system TBP-tetrachloroethylene, the nitration rate is maximal at a water content of 1.0-2.0 vol.%.
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Yoshimura, A.; Takai, M.; Matsuno, Y. Novel Process for Recycling Gold from Secondary Sources: Leaching of Gold by Dimethyl Sulfoxide Solutions Containing Copper Bromide and Precipitation with Water. Hydrometallurgy 2014, 149, 177– 182, DOI: 10.1016/j.hydromet.2014.08.003
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Novel process for recycling gold from secondary sources: Leaching of gold by dimethyl sulfoxide solutions containing copper bromide and precipitation with water
Yoshimura, Akihiro; Takai, Madoka; Matsuno, Yasunari
Hydrometallurgy (2014), 149 (), 177-182CODEN: HYDRDA; ISSN:0304-386X. (Elsevier B.V.)
A novel method for recovering gold from secondary sources, the leaching of gold using DMSO solns. contg. copper bromide followed by the pptn. of gold with water, is presented. Gold dissoln. was conducted in a DMSO soln. with 0.1-0.2 M of CuBr2 and 0-0.2 M of KBr at 333-348 K. The mechanism of gold dissoln. was investigated by electrochem. measurements. The pptn. of dissolved gold was performed by the addn. of water, during which the effects of the amt. of water and the pH on the recovery rate were investigated. It was found that the initial gold dissoln. rate in the DMSO solns. with CuBr2 was up to 37 mg cm- 2 h- 1, which is larger than those obtained with other leaching methods. The results of the electrochem. measurements indicate that the anodic dissoln. of gold in DMSO contg. CuBr2 occurs at relatively neg. potentials and is paired with the cathodic redn. of Cu2 + to Cu+. A recovery rate of gold up to 87% was obtained by pptn. with water. A small amt. of copper was pptd. with gold, which can be avoided by using water of lower pH, as is expected by the Eh-pH diagram. Our results demonstrate that a circulating system for gold leaching and recovery, which would offer a no. of advantages, including eco-friendliness, easy operation, low costs, and minimization of chem. sludge prodn., can be developed.
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Umehara, K.; Matsuno, Y. Fundamental Studies on a Recycling System for Precious and Rare Metals Using a Propylene Carbonate Solvent Containing CuBr₂ and KBr. Mater. Trans. 2015, 56, 1579– 1584, DOI: 10.2320/matertrans.M2015202
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Fundamental studies on a recycling system for precious and rare metals using a propylene carbonate solvent containing CuBr2 and KBr
Umehara, Kana; Matsuno, Yasunari
Materials Transactions (2015), 56 (9), 1579-1584CODEN: MTARCE; ISSN:1345-9678. (Japan Institute of Metals and Materials)
Previously we studied a novel process for recycling gold from secondary sources: the leaching of gold using DMSO solns. contg. copper bromide and pptn. with water, which could offer a no. of advantages, including eco-friendliness, ease of operation and low cost. In this study, we have further investigated a more environmentally benign solvent, Propylene Carbonate (PC), with CuBr2 and KBr for the leaching and recovery of precious and rare metals. The mechanism of dissoln. was investigated using electrochem. measurements. Metal wires were dissolved in a PC soln. with 0.2 M of CuBr2 and 0.2 M of KBr at 343 K. Next, 10 mL of dil. sulfuric acid aq. soln. at pH 1 was added to the soln. at ambient temp. and shaken to biphasically sep. the dissolved metals. The contents of each element in the sulfuric acid and PC phases were measured by ICP-OES. The results of the electrochem. measurements indicated that the anodic dissoln. of sample metals in the PC contg. CuBr2 occurred at relatively neg. potentials and was paired with the cathodic redn. of Cu2+ to Cu+. It was found that Au, Pd, Cu, Sn, Co, Ni and Zn could be dissolved at relatively fast rate, while Ag, Ta, Ti and W could not be dissolved. In addn., 98% of Au and 94% of Pd remained in the PC phase, while most other dissolved metals migrated to the sulfuric acid phase. This indicated that the dissolved Au and Pd could be effectively sepd. from other metals via biphasic sepn. with sulfuric acid. Next, the gold in the PC phase was recovered by the redn. of ascorbic acid or calcination. The cost anal. for recovering gold by this system resulted in 0.34 USD/g-Au.
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Bessel, C. A.; Denison, G. M.; DeSimone, J. M.; DeYoung, J.; Gross, S.; Schauer, C. K.; Visintin, P. M. Etchant Solutions for the Removal of Cu(0) in a Supercritical CO₂-Based “Dry” Chemical Mechanical Planarization Process for Device Fabrication. J. Am. Chem. Soc. 2003, 125, 4980– 4981, DOI: 10.1021/ja034091m
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Etchant solutions for the removal of Cu(0) in a supercritical CO2-based "dry" chemical mechanical planarization process for device fabrication
Bessel, Carol A.; Denison, Ginger M.; DeSimone, Joseph M.; DeYoung, James; Gross, Stephen; Schauer, Cynthia K.; Visintin, Pamela M.
Journal of the American Chemical Society (2003), 125 (17), 4980-4981CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
The microelectronics industry is focused on increasing chip complexity, improving the d. of electron carriers, and decreasing the dimensions of the interconnects into the sub-0.25 μm regime while maintaining high aspect ratios. Water-based chem. mech. planarization or polishing (CMP) faces several tech. and environmental challenges. Condensed CO2 has significant potential for replacing current CMP solvents as a "dry" etching medium because of its unique properties. In working toward a condensed CO2-based CMP process, the oxidn. and chelation of solid copper metal has been investigated in liq. and supercrit. CO2 using Et peroxydicarbonate and a β-diketone chelating agent.
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Visintin, P. M.; Bessel, C. A.; White, P. S.; Schauer, C. K.; DeSimone, J. M. Oxidative Dissolution of Copper and Zinc Metal in Carbon Dioxide with Tert-Butyl Peracetate and a β-Diketone Chelating Agent. Inorg. Chem. 2005, 44, 316– 324, DOI: 10.1021/ic049765o
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Oxidative Dissolution of Copper and Zinc Metal in Carbon Dioxide with tert-Butyl Peracetate and a β-Diketone Chelating Agent
Visintin, Pamela M.; Bessel, Carol A.; White, Peter S.; Schauer, Cynthia K.; DeSimone, Joseph M.
Inorganic Chemistry (2005), 44 (2), 316-324CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
A series of β-diketone ligands, R1COCH2COR2 [tmhdH (R1 = R2 = C(CH3)3); tfacH (R1 = CF3; R2 = CH3); hfacH (R1 = R2 = CF3)], in combination with tert-Bu peracetate (t-BuPA), have been investigated as etchant solns. for dissoln. of copper metal into carbon dioxide solvent. Copper removal in CO2 increases in the order tfacH < tmhdH < hfacH. A study of the reactions of the hfacH/t-BuPA etchant soln. with metallic copper and zinc was conducted in three solvents: scCO2 (supercrit. CO2); hexanes; CD2Cl2. The etchant soln./metallic zinc reaction produced a diamagnetic Zn(II) complex, which allowed NMR identification of the t-BuPA decompn. products as tert-Bu alc. and acetic acid. Gravimetric anal. of the amt. of zinc consumed, together with NMR studies, confirmed the 1:1:2 Zn:t-BuPA:hfacH reaction stoichiometry, showing t-BuPA to be an overall two-electron oxidant for Zn(0). The metal-contg. products of the copper and zinc reactions were characterized by elemental anal., IR spectroscopy, and, as appropriate, NMR spectroscopy and single-crystal X-ray diffraction [trans-M(hfac)2(H2O)(CH3CO2H) (1, M = Cu; 2, M = Zn)]. On the basis of the exptl. results, a working model of the oxidative dissoln. reaction is proposed, which delineates the key chem. variables in the etching reaction. These t-BuPA/hfacH etchant solns. may find application in a CO2-based chem. mech. planarization (CMP) process.
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Dunbar, A.; Omiatek, D. M.; Thai, S. D.; Kendrex, C. E.; Grotzinger, L. L.; Boyko, W. J.; Weinstein, R. D.; Skaf, D. W.; Bessel, C. A.; Denison, G. M.; DeSimone, J. M. Use of Substituted Bis(Acetylacetone)Ethylenediimine and Dialkyldithiocarbamate Ligands for Copper Chelation in Supercritical Carbon Dioxide. Ind. Eng. Chem. Res. 2006, 45, 8779– 8787, DOI: 10.1021/ie060947v
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Use of Substituted Bis(acetylacetone)ethylenediimine and Dialkyldithiocarbamate Ligands for Copper Chelation in Supercritical Carbon Dioxide
Dunbar, Andrew; Omiatek, Donna M.; Thai, Susan D.; Kendrex, Christopher E.; Grotzinger, Laurel L.; Boyko, Walter J.; Weinstein, Randy D.; Skaf, Dorothy W.; Bessel, Carol A.; Denison, Ginger M.; DeSimone, Joseph M.
Industrial & Engineering Chemistry Research (2006), 45 (26), 8779-8787CODEN: IECRED; ISSN:0888-5885. (American Chemical Society)
Chem.-mech. planarization (CMP) is a process of oxidizing and chelating the copper overburden present in an interconnect device while mech. polishing the surface of the wafer. Because the use of condensed CO2 as the solvent for CMP would be environmentally and tech. advantageous, several substituted bis(acetylacetonate)ethylenediimine (R4BAE, where R = CH3 or CF3) and lithium or sodium dialkyldithiocarbamate (M+(R2DTC-), where M+ = Li+ or Na+ and R = Et, Pr, Bu, or 1,1,1-trifluoroethyl) ligands were used with t-butylperacetate (t-BuPA, as oxidant) for the oxidative dissoln. of copper(0) in supercrit. (s.c.) CO2 at 40° and 170-210 bar or in hexanes at 40° and atm. pressure. The reaction products from the copper etching are Cu(R4BAE) or Cu(R2DTC)2, resp. The R2DTC- ligands had higher etch rates than the R4BAE ligands with comparable substituents, and the lithium dialkyldithiocarbamate salts gave higher copper etching rates than their sodium counterparts. The highest av. etch rates were obsd. for Li((CF3CH2)2DTC): 16.7 nm/min in s.c. CO2 and 11.2 nm/min in hexanes. While hexanes have similar phys. properties when compared to s.c. CO2, the rates of copper(0) removal with the R2DTC- ligands were 17-49% higher in s.c. CO2 than in hexanes at comparable temps. and solvent densities. SEM images of the postreaction copper surfaces using the various ligands showed significant variations in surface roughness. XPS measurements indicated that the lower R4BAE etch rates may be due to surface passivation by the R4BAE ligands and/or the Cu(R4BAE) complexes.
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Weinstein, R. D.; Richard, J. G.; Bessel, C. A.; Hanlon, W. H.; Skaf, D. W. The Removal of Copper with Dialkyldithiocarbamate Ligands in Condensed Carbon Dioxide. Chem. Eng. Technol. 2008, 31, 575– 581, DOI: 10.1002/ceat.200700444
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The removal of copper with dialkyldithiocarbamate ligands in condensed carbon dioxide
Weinstein, Randy D.; Richard, Joshua G.; Bessel, Carol A.; Hanlon, William H.; Skaf, Dorothy W.
Chemical Engineering & Technology (2008), 31 (4), 575-581CODEN: CETEER; ISSN:0930-7516. (Wiley-VCH Verlag GmbH & Co. KGaA)
The global kinetics of the oxidn. and removal of Cu(0) foil were examd. in liq. and supercrit. CO2 using tert-Bu peracetate (t-BuPA) as the oxidant and dialkyldithiocarbamate Li salts (Li+R2DTC-, with R =Et, Pr, or n-butyl) as the chelating agent. The pressure was kept const. (240 bars) for all reactions as d. was not found to affect the kinetics at pressures ∼150 bars. Temp. was 25-60° and the concns. of the oxidant and chelating agents were varied to det. the obsd. overall reaction orders for each species. Under our reaction conditions, the obsd. global reaction was independent of oxidant concn. but varied due to the R2DTC- concn. The Et2DTC- had an obsd. half order reaction dependence, indicating a complex reaction mechanism while the other 2 R2DTC- had 1st order dependence suggesting diffusion limitations. Arrhenius expressions were detd. by the temp. dependent kinetics of the product, Cu(R2DTC)2, formation. The apparent activation energy, Ea, for the Et2DTC- was 66 KJ/mol, confirming a complex reaction mechanism due to its large value. The apparent activation energies for the Pr2DTC- and Bu2DTC- were 14 and 17 KJ/mol, resp. These low energies are consistent with diffusion limitation.
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Rasadujjaman, M.; Nakamura, Y.; Watanabe, M.; Kondoh, E.; Baklanov, M. R. Supercritical Carbon Dioxide Etching of Transition Metal (Cu, Ni, Co, Fe) Thin Films. Microelectron. Eng. 2016, 153, 5– 10, DOI: 10.1016/j.mee.2015.12.018
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Supercritical carbon dioxide etching of transition metal (Cu, Ni, Co, Fe) thin films
Rasadujjaman, Md.; Nakamura, Yoshiki; Watanabe, Mitsuhiro; Kondoh, Eiichi; Baklanov, Mikhail R.
Microelectronic Engineering (2016), 153 (), 5-10CODEN: MIENEF; ISSN:0167-9317. (Elsevier B.V.)
Supercrit. CO2 is a promising zero-surface-tension, highly diffusive solvent, which creates a uniform reaction environment that dissolves low-volatility metal compds. Here we report a novel etching technique for transition metal (Cu, Ni, Co, and Fe) thin films in supercrit. CO2 (scCO2). The metals were removed by reacting with the chelating agent, hexafluoroacetylacetone, by dissolving the product compds. in scCO2. The operating temps. were 100-250 °C and pressure was fixed at 10 MPa. The changes in the optical transmittance and thickness of the films indicated etching in the scCO2. Scanning electron microscope observation and surface probe microscope anal. confirmed that there was no significant film agglomeration, in particular, and that the Fe and Co films were uniformly etched.
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137
Favier, I.; Duñach, E. Novel Electrosynthesis of Metallic Bis(Trifluoromethanesulfonyl) Imides. Tetrahedron Lett. 2003, 44, 2031– 2032, DOI: 10.1016/S0040-4039(03)00214-4
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Novel electrosynthesis of metallic bis(trifluoromethanesulfonyl) imides
Favier, Isabelle; Dunach, Elisabet
Tetrahedron Letters (2003), 44 (10), 2031-2032CODEN: TELEAY; ISSN:0040-4039. (Elsevier Science Ltd.)
The prepn. of bis(trifluoromethanesulfonyl) imide salts of various metals were effected in good yields, under clean, mild and anhyd. conditions, by using a simple electrochem. methodol.
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Abbott, A. Electrochemistry in Media of Low Dielectric Constant. Chem. Soc. Rev. 1993, 22, 435– 440, DOI: 10.1039/cs9932200435
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138
Electrochemistry in media of low dielectric constant
Abbott, Andrew
Chemical Society Reviews (1993), 22 (6), 435-40CODEN: CSRVBR; ISSN:0306-0012.
A review 29 refs. Solvents of low dielec. const. are practical and interesting media in which to carry out electrochem. investigations. There are some problems assocd. with low dielec. const. media, most noticeably low soly. for ionic species and low cond. Methods of circumventing many of these problems are highlighted. Probably their most useful property is the low degree of interaction with the solute which means that the electron-transfer process can be investigated without having to account for anomalous solvent effects. The high chem. and electrochem. stability of these solvents allows a wide range of reactions to be investigated which are difficult or impossible to carry out in other media.
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Kharisov, B. I.; Blanco, L. M.; Salinas, M. V.; Garnovskii, A. D. Direct Synthesis of Copper Dimethyldithiocarbamate Derivatives: An Optimization Using Ultrasonic Treatment. J. Coord. Chem. 1999, 47, 135– 143, DOI: 10.1080/00958979908024548
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139
Direct synthesis of copper dimethyldithiocarbamate derivatives: an optimization using ultrasonic treatment
Kharisov, B. I.; Blanco, L. M.; Salinas, M. V.; Garnovskii, A. D.
Journal of Coordination Chemistry (1999), 47 (1), 135-143CODEN: JCCMBQ; ISSN:0095-8972. (Gordon & Breach Science Publishers)
A comparison of the synthetic approaches for Cu dimethyldithiocarbamate complexes by oxidative and electrochem. dissoln. of metallic Cu in different nonaq. solvents is reported. The influence of ultrasound on the synthesized products and on the reaction yields is also studied. The results show the influence of solvent on the structure and on the increase in rate of metal dissoln. from simultaneous ultrasonic treatment.
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Abstract
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Figure 1
Figure 1. Number of publications on dissolution of metals in organic solvents.
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Figure 2
Figure 2. Overview of the organic leaching systems and the metals that have been studied for oxidative dissolution in the corresponding leaching systems.
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Figure 3
Figure 3. Screening dissolution test for the SmCo₅ (top) and Sm₂Co₁₇ (bottom) permanent magnets at 20 min in 1 vol % Br₂ in EG, DMF, EtOH, MeOAc, and EtOAc. The recovery yields, η (%), were the ratio of the concentration of a metal in solution after leaching for 20 min to the concentration of the same metal if all the content of the coating would be dissolved in solution. Reprinted from ref (34). Copyright 2019 Royal Society of Chemistry under [CC BY-NC 3.0] [https://creativecommons.org/licenses/by-nc/3.0/].
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Scheme 1
Scheme 1. Chlorination of Molybdenum by Chlorine in DMF
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Figure 4
Figure 4. Effect of water on dissolution of metals in solutions of chlorine in DMF. (Data were extracted from ref (27).)
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Scheme 2
Scheme 2. Complex Formed between DMF and HCl
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Scheme 3
Scheme 3. Structures and Abbreviations of the Reported Organic Ligands to Form Halogen Adducts
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Scheme 4
Scheme 4. Oxidative Dissolution of Gold and Palladium with Me₂dazdt·2I₂ in Organic Solvent at Room Temperature
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Scheme 5
Scheme 5. Synthesis of a Palladium Complex from a Diiodine Tellurium Adduct
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Figure 5
Figure 5. Molecular structure of (a) [CdI(Me₂pipdt)₂]I₃ and (b) [HgI₂(Me₂pipdt)], with thermal ellipsoids depicted at the 30% probability level. Symmetry code = −x; y; ¹/₂ – z. Reprinted with permission from ref (53). Copyright 2014 Elsevier B.V.
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Scheme 6
Scheme 6. Oxidative Dissolution Reaction of Platinum by [Me₂Pipdt]I₃ in Acetonitrile (Reflux for 4 days)
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Scheme 7
Scheme 7. Oxidative Dissolution of Gold by Et₄TDS/I₂ in Acetone at Room Temperature with the Formation of Four Complexes by Varying the Molar Ratio of Et₄TDS to I₂^a
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^aReprinted with permission from ref (58). Copyright 2013 WILEY-VCH Verlag GmbH & Co. KGaA.
Figure 6
Figure 6. Leaching of palladium from spent catalyst by organic triiodides in methylethylketone (MEK) under reflux for 7 days. Reprinted with permission from ref (55). Copyright 2017 American Chemical Society.
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Scheme 8
Scheme 8. Structures of Iodocarbene Iodide and Gold Complexes Formed by Reaction between Compound (a) and Gold^a
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^aThe names of the compounds are (a) N,N-dimethyliodomethyleneiminium iodide; (b) bis(N,N’-dimethylamino)iodomethylene iodide; (c) 2-iodo-1,3-dimethylimidazolium iodide; (d) triiodo[(dimethylamino)methylene]gold(III); (e) iodo(dimethylamino)methylenegold(I); and (f) [AuI₂(CHNMe₂)₂]⁺[AuI₂]⁻.
Figure 7
Figure 7. Crystal structures of carbene complexes: the urea-derived complexes 10-mono (top, left, d_Au–C = 2.041(7) Å) and 10-bis (bottom, left, d_Au–C = 2.085(4) Å) and the corresponding NHC-complexes 11-mono (top, right, d_Au–C = 2.074(15) Å) and 11-bis (bottom, right, d_Au–C = 2.021(7) Å). Thermal ellipsoids at 50% probability. Reprinted with permission from ref (63). Copyright 2017 Wiley-VCH Verlag GmbH & Co. KGaA.
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Figure 8
Figure 8. Gold leaching from ores by N-bromosuccinimide/pyridine (NBS/Py). (a) Scanning electron microscopy (SEM) image of the gold ore; (b) corresponding metal contents in the raw gold ore; (c) effect of pH on the leaching yield of gold by different methods; (d) effect of pH on the leaching yields for the collective metals contained in the gold ores. The NBS and pyridine concentrations were 10 and 100 mm, respectively. Reprinted with permission from ref (1). Copyright 2017 Wiley-VCH Verlag GmbH & Co. KGaA.
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Scheme 9
Scheme 9. Chemical Structures of GEOBROM 3114 (left) and GEOBROM 5500 (right)
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Scheme 10
Scheme 10. Sequence of Reactions between DMSO and HBr
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Scheme 11
Scheme 11. Reactions between DMSO and HCl
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Scheme 12
Scheme 12. Reactions between DMSO and NH₄X
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Figure 9
Figure 9. Illustration of selective dissolution of gold, palladium, and platinum in organic aqua regia. A silicon substrate was metallized with a Pd/Au/Pt layer (250 nm thick each by electron-beam evaporation or direct current sputtering, with chromium used as the adhesion layer). The top row of images shows the photographs of the Pd/Au/Pt metallization layer on a silicon substrate during the process of selective dissolution. Reprinted with permission from ref (84). Copyright 2010 WILEY-VCH Verlag GmbH & Co. KGaA.
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Scheme 13
Scheme 13. Structure of Cations of Trichloride ILs^a
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^aReprinted from ref (94). Copyright 2018 Royal Society of Chemistry under [CC BY-NC 3.0] [https://creativecommons.org/licenses/by-nc/3.0/].
Figure 10
Figure 10. Extraction of gold and silver (top) and base metals (bottom) from a complex sulfidic gold-bearing ore using thiourea leaching with ILs with the [Bmim]⁺ cation and different anions (50 °C, 48 h leaching). Reprinted with permission from ref (108). Copyright 2007 Elsevier B.V.
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Scheme 14
Scheme 14. Structure of 4-Pyridinethiol (4-PS) That Was Effective for Dissolution of Gold and Other Organic Components with Similar Structures to 4-Pyridinethiol
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Figure 11
Figure 11. Proposed reaction mechanism for the oxidation of gold with 4-pyrindinethiol (4-PS) in alcohol solutions in open air. Reproduced with permission from ref (119). Copyright 2007 American Chemical Society.
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Scheme 15
Scheme 15. Chemical Structures of Oxidizing Agents and Chelating Agents for Dissolution of Copper in Supercritical CO₂
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References
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This article references 139 other publications.
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  Methanesulfonic acid (MSA) is a green acid with a remarkably high soly. for several speciality and base metals including lead, making it an interesting leaching agent for metals. MSA is safer and less toxic than the mineral acids (HCl, H2SO4, HNO3) currently employed for leaching metals from primary and secondary sources. In this study, MSA was tested for the leaching of lead and zinc from the iron-rich jarosite residue of the zinc industry. The leaching of lead, zinc and iron increased as a function of the MSA concn. in water up to 90 vol% MSA. Higher MSA concns. resulted in ppt. formation due to the limited soly. of the iron and zinc methanesulfonate salts in water-lean MSA. Leaching with pure MSA resulted in a pregnant leach soln. (PLS) comprising most of the lead and zinc, and a ppt. comprising the majority of the iron and a fraction of the zinc originally present in the jarosite. The optimization of the leaching conditions showed that increasing the liq.-to-solid ratio or temp. increased the leaching efficiencies of the metals, esp. of lead. The leaching under optimized conditions was successfully performed on a larger scale using a temp.-controlled batch leaching reactor. The metal/iron mass ratio increased from 1/4 for Pb/Fe, and from 1/7 for Zn/Fe in the initial jarosite, to over 2.66/1 and 1/2, in the PLS, resp. The remaining MSA in the PLS was recovered by vacuum distn. and successfully reused for three leaching cycles.
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  Selective recovery of zinc from goethite residue in the zinc industry using deep-eutectic solvents
  Rodriguez Rodriguez, Nerea; Machiels, Lieven; Onghena, Bieke; Spooren, Jeroen; Binnemans, Koen
  RSC Advances (2020), 10 (12), 7328-7335CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
  A review. Several deep-eutectic solvents (DESs) were tested for the valorisation of goethite residue produced by the zinc industry. The objective of the work was to selectively recover zinc from the iron-rich matrix using deep-eutectic solvents as lixiviants. The effect of the type of hydrogen bond donor and hydrogen bond acceptor of the deep-eutectic solvent on the leaching efficiency was studied. Levulinic acid-choline chloride (xChCl = 0.33) (LevA-ChCl) could selectively leach zinc from the iron-rich matrix, and it was selected as the best-performing system to be used in further study. The leaching process was optimized in terms of temp., contact time, liq.-to-solid ratio and water content of the deep-eutectic solvent. The role of the choline cation on the leaching process was investigated by considering the leaching properties of a LevA-CaCl2 mixt. The goethite residue was also leached with pure levulinic acid. The results were compared to a purely hydrometallurgical approach using sulfuric acid leaching. Leaching with LevA-ChCl resulted in higher selectivity compared to the conventional "hot leaching" with 80 g L-1 sulfuric acid. Furthermore, a slightly higher zinc recovery and comparable selectivity for zinc over iron were achieved with LevA-ChCl compared to conventional "neutral leaching" with 10 g L-1 sulfuric acid.
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7. 7
  European Commission. Communication from the Commission to the European Parliament, the Council, the Eurpean Economic and Social Committee and the Committee of the Regions on the 2017 List of Critical Raw Materials for the EU. 2017.
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  There is no corresponding record for this reference.
8. 8
  Ellis, L. US Department of the Interior - Office of the Secretary: Final List of Critical Minerals 2018. Fed. Regist. 2018, 83, 23295– 23296
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  There is no corresponding record for this reference.
9. 9
  Sheng, P. P.; Etsell, T. H. Recovery of Gold from Computer Circuit Board Scrap Using Aqua Regia. Waste Manage. Res. 2007, 25, 380– 383, DOI: 10.1177/0734242X07076946
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  9
  Recovery of gold from computer circuit board scrap using aqua regia
  Sheng, Peter P.; Etsell, Thomas H.
  Waste Management & Research (2007), 25 (4), 380-383CODEN: WMARD8 ISSN:. (Sage Publications Ltd.)
  Computer circuit board scrap was first treated with one part concd. nitric acid and two parts water at 70° for 1 h. This step dissolved the base metals and thereby liberated the chips from the boards. After solid-liq. sepn., the chips, intermixed with some metal flakes and tin oxide ppt., were mech. crushed to liberate the base and precious metals contained within the protective plastic or ceramic chip cases. The base metals in the crushed product were dissolved by leaching again with the same type of nitric acid-water soln. The remaining solid constituents, crushed chips and resin, plus solid particles of gold, were leached with aqua regia at various times and temps. Gold was pptd. from the leachate with ferrous sulfate.
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10. 10
  Gökelma, M.; Birich, A.; Stopic, S.; Friedrich, B. A Review on Alternative Gold Recovery Re-Agents to Cyanide. J. Mater. Sci. Chem. Eng. 2016, 04, 8– 17, DOI: 10.4236/msce.2016.48002
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  There is no corresponding record for this reference.
11. 11
  Binnemans, K.; Jones, P. T. Solvometallurgy: An Emerging Branch of Extractive Metallurgy. J. Sustain. Metall. 2017, 3, 570– 600, DOI: 10.1007/s40831-017-0128-2
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  There is no corresponding record for this reference.
12. 12
  Li, X.; Monnens, W.; Li, Z.; Fransaer, J.; Binnemans, K. Solvometallurgical Process for Extraction of Copper from Chalcopyrite and Other Sulfidic Ore Minerals. Green Chem. 2020, 22, 417– 426, DOI: 10.1039/C9GC02983D
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  12
  Solvometallurgical process for extraction of copper from chalcopyrite and other sulfidic ore minerals
  Li, Xiaohua; Monnens, Wouter; Li, Zheng; Fransaer, Jan; Binnemans, Koen
  Green Chemistry (2020), 22 (2), 417-426CODEN: GRCHFJ; ISSN:1463-9262. (Royal Society of Chemistry)
  Extn. of copper from sufidic ores, either by pyrometallurgy or hydrometallurgy, has various limitations. In this study, a solvometallurgical process for the extn. of copper from sulfidic ore minerals (chalcopyrite, bornite, chalcocite and digenite) was developed by using an org. lixiviant (FeCl3 as oxidizing agent and ethylene glycol (EG) as org. solvent). All the studied copper sulfide minerals could be leached efficiently with a FeCl3-EG soln. Other lixiviant systems, namely CuCl2-EG, FeCl3-ethanol and FeCl3-propylene glycol could also ext. copper, but they did not perform as well as the FeCl3-EG solns. The mechanistic study of chalcopyrite leaching in FeCl3-EG solns. confirmed that the leaching products of chalcopyrite were FeCl2, CuCl and solid elemental sulfur, where the Fe(II) and Cu(I) were quantified by UV-Vis absorption spectroscopy and solid sulfur was identified by powder x-ray diffraction. A kinetic study showed that the leaching process was a surface chem. controlled process and the apparent activation energy was calcd. to be 60.1 kJ mol-1. Subsequently, electrodeposition of copper from the pregnant leachate was investigated, and SEM-energy-dispersive x-ray anal. showed that uniform cubic cryst. deposits of pure copper were produced. Meanwhile, the Fe(III) was regenerated by oxidizing Fe(II) at the anode, with a Morgane membrane in between two electrode compartments to prevent the transfer of Fe(III) to the cathode. Finally, a closed-loop solvometallurgical process was designed with three operational steps: leaching, electrodeposition and removal of Fe(II). The regeneration of the FeCl3-EG soln. and the use of EG contribute to the sustainability and the greenness of the process.
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13. 13
  Li, Z.; Zhang, Z.; Smolders, S.; Li, X.; Raiguel, S.; Nies, E.; De Vos, D. E.; Binnemans, K. Enhancing Metal Separations by Liquid–Liquid Extraction Using Polar Solvents. Chem. - Eur. J. 2019, 25, 9197– 9201, DOI: 10.1002/chem.201901800
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  13
  Enhancing Metal Separations by Liquid-Liquid Extraction Using Polar Solvents
  Li, Zheng; Zhang, Zidan; Smolders, Simon; Li, Xiaohua; Raiguel, Stijn; Nies, Erik; De Vos, Dirk E.; Binnemans, Koen
  Chemistry - A European Journal (2019), 25 (39), 9197-9201CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
  The less polar phase of liq.-liq. extn. systems was studied extensively for improving metal sepns.; however, the role of the more polar phase was overlooked for far too long. Herein, we investigate the extn. of metals from a variety of polar solvents and demonstrate that, the influence of polar solvents on metal extn. is so significant that extn. of many metals can be largely tuned, and the metal sepns. can be significantly enhanced by selecting suitable polar solvents. Furthermore, a mechanism on how the polar solvents affect metal extn. is proposed based on comprehensive characterizations. The method of using suitable polar solvents in liq.-liq. extn. paves a new and versatile way to enhance metal sepns.
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14. 14
  Li, Z.; Mercken, J.; Li, X.; Riaño, S.; Binnemans, K. Efficient and Sustainable Removal of Magnesium from Brines for Lithium/Magnesium Separation Using Binary Extractants. ACS Sustainable Chem. Eng. 2019, 7, 19225– 19234, DOI: 10.1021/acssuschemeng.9b05436
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  14
  Efficient and Sustainable Removal of Magnesium from Brines for Lithium/Magnesium Separation Using Binary Extractants
  Li, Zheng; Mercken, Jonas; Li, Xiaohua; Riano, Sofia; Binnemans, Koen
  ACS Sustainable Chemistry & Engineering (2019), 7 (23), 19225-19234CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
  Lithium is becoming increasingly important due to its essential role in lithium-ion batteries. Over 70% of the global lithium resources are found in salt lake brines, but lithium is always accompanied by magnesium. It is a challenge to efficiently sep. lithium from magnesium in brines. The state-of-the-art processes for lithium/magnesium sepn. either consume large quantities of chems. and generate large amts. of waste or are energy-intensive. In this study, we develop a sustainable solvent extn. process based on binary extractants to efficiently sep. lithium and magnesium. A binary extractant composed of Aliquat 336 and Versatic Acid 10, [A336][V10], was prepd. and investigated for removal of magnesium from both a (synthetic) concd. brine (106 g L-1 Mg and 10 g L-1 Li) and an (synthetic) original brine (15 g L-1 Mg, 80 g L-1 Na and 0.2 g L-1 Li). Through batch counter-current expts. and mixer-settler expts., it was found that [A336][V10] is able to quant. remove magnesium from the original brine in three continuous counter-current extn. stages with as little as about 10% coextn. of lithium. The loaded org. phase can be stripped and regenerated by water. The whole process (extn. and stripping) does not consume any acid or base but makes use of the differences in the chloride concn. during extn. and stripping. This process is an environmentally friendly alternative to the state-of-the-art processes and represents a step forward in the sustainable prodn. of Li2CO3 from brines. The binary extractant [A336][V10] removes magnesium from brine solns. selectively and efficiently without consumption of any acid or base.
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15. 15
  Li, X.; Li, Z.; Orefice, M.; Binnemans, K. Metal Recovery from Spent Samarium-Cobalt Magnets Using a Trichloride Ionic Liquid. ACS Sustainable Chem. Eng. 2019, 7, 2578– 2584, DOI: 10.1021/acssuschemeng.8b05604
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  15
  Metal Recovery from Spent Samarium-Cobalt Magnets Using a Trichloride Ionic Liquid
  Li, Xiaohua; Li, Zheng; Orefice, Martina; Binnemans, Koen
  ACS Sustainable Chemistry & Engineering (2019), 7 (2), 2578-2584CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
  Recycling of samarium-cobalt (SmCo) magnets is essential due to the limited resources of the mentioned metals and their high economic importance. The ionic liq. (IL) trihexyltetradecylphosphonium trichloride, [P666,14][Cl3], which can safely store Cl gas in the form of the trichloride anion, was used as an oxidizing solvent for the recovery of metals from spent SmCo magnets. The dissoln. was studied considering various mixts. of the ILs [P666,14][Cl3] and [P666,14]Cl, solid-to-liq. ratios and different temps. The results showed that the max. capacity of [P666,14][Cl3] for SmCo magnets was 71±1 mg/g of [P666,14][Cl3], in the presence of an extra source of coordinating Cl-. The max. loading of the IL could be reached within 3 h at 50°. Four stripping steps effectively removed all metals from the loaded IL, where NaCl soln. (3 mol/L), twice water and ammonia soln. (3 mol/L) were used consecutively as the stripping solvents. The regenerated IL showed a similar dissoln. performance as fresh IL. Oxidative dissoln. of metals in trichloride ILs is easily transferable to the recycling of valuable metals from other end-of-life products such as Nd-Fi-B magnets and Ni metal hydride batteries.
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16. 16
  Deferm, C.; Malaquias, J. C.; Onghena, B.; Banerjee, D.; Luyten, J.; Oosterhof, H.; Fransaer, J.; Binnemans, K. Electrodeposition of Indium from the Ionic Liquid Trihexyl(Tetradecyl)Phosphonium Chloride. Green Chem. 2019, 21, 1517– 1530, DOI: 10.1039/C8GC03389G
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  16
  Electrodeposition of indium from the ionic liquid trihexyl(tetradecyl)phosphonium chloride
  Deferm, Clio; Malaquias, Joao C.; Onghena, Bieke; Banerjee, Dipanjan; Luyten, Jan; Oosterhof, Harald; Fransaer, Jan; Binnemans, Koen
  Green Chemistry (2019), 21 (6), 1517-1530CODEN: GRCHFJ; ISSN:1463-9262. (Royal Society of Chemistry)
  The electrochem. behavior of In in the ionic liq. trihexyl(tetradecyl)phosphonium chloride (Cyphos IL 101) was studied. Cyphos IL 101 1st had to be purified, as the impurities present in com. Cyphos IL 101 interfered with the electrochem. measurements. Electrochem. deposition of In metal from this electrolyte occurs without H evolution, increasing the cathodic current efficiency compared to deposition from H2O and avoiding porosity within the deposited metal. Indium(III) is the most stable oxidn. state in the ionic liq. This ion is reduced in two steps, 1st from In(III) to In(I) and subsequently to In(0). The high thermal stability of Cyphos IL 101 allowed the electrodeposition of In at 120° and 180°. At 180° In was deposited as liq. In which allows for the easy sepn. of the In and the possibility to design a continuous electrowinning process. On Mo, In deposits as liq. droplets even below the m.p. of In. This was explained by the combination of m.p. depression and undercooling. The possibility to sep. In from Fe and Zn by electrodeposition was tested. It is possible to sep. In from Zn by electrodeposition, but Fe deposits together with In.
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17. 17
  Abbott, A. P.; Frisch, G.; Gurman, S. J.; Hillman, A. R.; Hartley, J.; Holyoak, F.; Ryder, K. S. Ionometallurgy: Designer Redox Properties for Metal Processing. Chem. Commun. 2011, 47, 10031– 10033, DOI: 10.1039/c1cc13616j
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  Ionometallurgy: designer redox properties for metal processing
  Abbott, A. P.; Frisch, G.; Gurman, S. J.; Hillman, A. R.; Hartley, J.; Holyoak, F.; Ryder, K. S.
  Chemical Communications (Cambridge, United Kingdom) (2011), 47 (36), 10031-10033CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
  The first electrochem. series in a deep eutectic solvent is described. Speciation resulting from the unusual chem. of the choline chloride based deep eutectic solvent is used to explain both similarities and differences from aq. media. Examples are given of how these differences can be exploited in technol. important systems as a solvent in hydrometallurgical systems.
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18. 18
  Larsen, R. P. Dissolution of Uranium Metal and Its Alloys. Anal. Chem. 1959, 31, 545– 549, DOI: 10.1021/ac50164a026
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  18
  Solution of uranium metal and its alloys
  Larsen, Robert P.
  (1959), 31 (), 545-9CODEN: ANCHAM; ISSN:0003-2700.
  The most useful methods for the soln. of U metal and its alloys are reviewed, with particular emphasis on the prepn. of solns. for analysis. The behavior of the metal and its alloys in the common acids, EtOAc solns. of Br and HCl, and NaOH-H2O2 mixts. is described. Recommendations for dissolving each of a wide variety of U alloys are summarized in tabular form. 10 references.
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19. 19
  Eberle, A. R.; Lerner, M. W. Determination of Boron in Beryllium, Zirconium, Thorium, and Uranium Dissolution in Bromine-Methanol. Anal. Chem. 1960, 32, 146– 149, DOI: 10.1021/ac60158a001
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  19
  Determination of boron in beryllium, zirconium, thorium, and uranium. Dissolution in bromine-methanol
  Eberle, A. R.; Lerner, M. W.
  (1960), 32 (), 146-9CODEN: ANCHAM; ISSN:0003-2700.
  B (0.10-500 p.p.m.) in Be, Zr, Th, and U can be detd. by dissoln. of the metal in Br-MeOH followed by distn. of the boron ester and color development with diaminochrysazin (cf. Cogbill and Yoe, C.A. 51, 17571e). In the case of Zr, Th, and U, more Br than that required for stoichiometry is added to enable a reasonably fast reaction, the excess Br being consumed by Be scavenger. More than recommended quantities of Be scavenger tend to give low results. The recovery of B is complete even by distg. 50% of the anhyd. reaction mixt. only, thus saving time and minimizing the quantities in the distillate of Br and bromide which in large amts. may interfere. The fluoride ion in the sample is not distd. The distillate is treated with lime suspension to hydrolyze the Me borate and to prevent hydrolysis of the resulting salt to the volatile free acid. On evapn. H2SO4 is added to the residue prior to absorbance measurements. The precision and accuracy of the method are good. The analysis of 2 samples of Zircaloy (15 detns.) showed an av. deviation of ±0.00058 and ±0.00107, resp.
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20. 20
  Beeghly, H. F. Determination of Aluminum Nitride Nitrogen in Steel. Anal. Chem. 1949, 21, 1513– 1519, DOI: 10.1021/ac60036a024
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  20
  Determination of aluminum nitride nitrogen in steel
  Beeghly, H. F.
  (1949), 21 (), 1513-19CODEN: ANCHAM; ISSN:0003-2700.
  If a sample of steel is extd. with Br and MeOAc under a reflux condensor, all the Fe is dissolved and the residue contains AlN. The N can be detd. by the procedure described in (C.A. 36, 1866.9). A suitable app. is shown; 32 references.
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21. 21
  Busheina, I. S.; Headridge, J. B. Studies in Chemical Phase Analysis Part I. Determination of the Solubilities of Elements in Certain Organic Solvent - Bromine Mixtures. Analyst 1980, 105, 600– 604, DOI: 10.1039/an9800500600
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  21
  Studies in chemical phase analysis. Part 1. Determination of the solubilities of elements in certain organic solvent-bromine mixtures
  Busheina, I. S.; Headridge, J. B.
  Analyst (Cambridge, United Kingdom) (1980), 105 (1251), 600-4CODEN: ANALAO; ISSN:0003-2654.
  The solubilities of Al, Cr, Co, Cu, Fe, Pb, Mn, Mo, Ni, Nb, P, Si, S, Sn, Ti, W, and V were detd. at 25° in org. solvent-Br mixts. (10:1) after refluxing. MeOAc, BuOAc, and MeCN were used as solvents. Pb, Mo, Si, and W were not appreciably sol. in these solvents. E.g., the soly. of Al was 3.1, 2.8, and 3.4 g/100 mL in MeOAc-Br, BuOAc-Br, and MeCN-Br solns., resp., compared with <0.02, <0.01, and <0.02 g/100 mL, resp., for W.
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22. 22
  Abou Zeid, G. T.; Headridge, J. B. Studies in Chemical Phase Analysis Part III.*Determination of the Solubilities of Certain Elements and Compounds Pertinent to Steels in Organic Solvent - Halogen Mixtures with Particular Emphasis on Manganese Silicon Nitride. Analyst 1982, 107, 200– 205, DOI: 10.1039/an9820700200
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  22
  Studies in chemical phase analysis. Part III. Determination of the solubilities of certain elements and compounds pertinent to steels in organic solvent-halogen mixtures with particular emphasis on manganese silicon nitride
  Abou Zeid, G. T.; Headridge, J. B.
  Analyst (Cambridge, United Kingdom) (1982), 107 (1271), 200-5CODEN: ANALAO; ISSN:0003-2654.
  To assist in the development of methods for the detn. of MnSiN2 in steels contg. Al or Nb nitrides, the solubilities of Fe and MnSiN2 were detd. in MeOH and Me acetate each contg. a halogen or an interhalogen compd. The best solvent for the detn. of Al nitride or Nb nitride in the presence of MnSiN2 is ICl3-Me acetate under reflux. However, for the isolation of MnSiN2 together with the more stable nitrides, I2-Me acetate is the best solvent. The solubilities of Fe and certain other elements and of some compds. of Fe and Mn were detd. in I2-MeOH soln. The solvent is recommended for the isolation of Fe(II) and Mn(II) oxides from steels but Fe(II) and Mn(II) sulfides and cementite are appreciably attacked by the solvent.
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23. 23
  Busheina, I. S.; Headridge, J. B. Studies in Chemical Phase Analysis Part II. Determination of the Solubilities of Carbides, Nitrides, Oxides and Sulphides in Certain Organic Solvent - Bromine Mixtures. Analyst 1981, 106, 221– 226, DOI: 10.1039/an9810600221
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  23
  Studies in chemical phase analysis. Part II. Determination of the solubilities of carbides, nitrides, oxides, and sulfides in certain organic solvent-bromine mixtures
  Busheina, I. S.; Headridge, J. B.
  Analyst (Cambridge, United Kingdom) (1981), 106 (1259), 221-6CODEN: ANALAO; ISSN:0003-2654.
  The solubilities of 5 carbides, 7 nitrides, 16 oxides, and 11 sulfides were detd. at 25° in MeOAc- and MeCN-Br mixts. (10:1) after shaking at room temp. and refluxing. AlN, Cr2N, NbN, TiN, and VN had very low solubilities, esp. in MeOAc-Br at room temp. Fe3C and Fe and Mn nitrides were extensively decompd. with the Fe and Mn passing into soln. The oxides were sparingly sol. but the sulfides were appreciably sol.
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24. 24
  Strubbe, K.; Gomes, W. P. Bromine-Methanol as an Etchant for Semiconductors: A Fundamental Study on GaP: I. Etching Behavior of N- and P-Type. J. Electrochem. Soc. 1993, 140, 3294– 3300, DOI: 10.1149/1.2221026
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  24
  Bromine-methanol as an etchant for semiconductors: a fundamental study on gallium phosphide. I. Etching behavior of n- and p-type GaP
  Strubbe, K.; Gomes, W. P.
  Journal of the Electrochemical Society (1993), 140 (11), 3294-300CODEN: JESOAN; ISSN:0013-4651.
  Electrochem. and etching expts. were performed at n- and p-type GaP single crystals in the commonly used etchant bromine-methanol to study the fundamental aspects of the etching reaction. The etching properties of these methanolic bromine solns. were similar to those of bromine solns. in which water is used as the solvent; thus, e.g., as in water, the etching kinetics and morphologies at the (111) and (111) faces are markedly different. In many cases of practical etching, methanol may be substituted by water as the solvent for bromine. The results allow one to propose an overall reaction equation for the etch process as well as a detailed mechanism involving radical decompn. intermediates of the semiconductor. These intermediates may further react chem. either with species formed in the etch process itself or with ligands from the soln.
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25. 25
  Sullivan, M. V.; Kolb, G. A. The Chemical Polishing of Gallium Arsenide in Bromine-Methanol. J. Electrochem. Soc. 1963, 110, 585, DOI: 10.1149/1.2425820
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  Chemical polishing of gallium arsenide in bromine-methanol
  Sullivan, M. V.; Kolb, G. A.
  Journal of the Electrochemical Society (1963), 110 (), 585-7CODEN: JESOAN; ISSN:0013-4651.
  Best chem. polishing of GaAs is obtained by combining the etchant MeOH contg. a few percent Br with intensive stirring. Etch rates are shown for different crystal faces of GaAs as a function of the Br concn. and the pressure exerted on the crystal. The {111} face of GaAs is the most difficult to polish, but a high polish can be obtained on it by reducing the Br content to 0.0025%.
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26. 26
  Drobot, N. F.; Noskova, O. A.; Ovchinnikova, N. A.; Zvereva, G. A.; Larin, G. M.; Krenev, V. A.; Trifonova, E. N.; Drobot, D. V. Complex Formation during Molybdenum Chlorination in DMF Medium. Russ. J. Coord. Chem. 2003, 29, 474– 477, DOI: 10.1023/A:1024774829021
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  Complex Formation During Molybdenum Chlorination in DMF Medium
  Drobot, N. F.; Noskova, O. A.; Ovchinnikova, N. A.; Zvereva, G. A.; Larin, G. M.; Krenev, V. A.; Trifonova, E. N.; Drobot, D. V.
  Russian Journal of Coordination Chemistry (Translation of Koordinatsionnaya Khimiya) (2003), 29 (7), 474-477CODEN: RJCCEY; ISSN:1070-3284. (MAIK Nauka/Interperiodica Publishing)
  IR and EPR studies of solns. formed after Mo chlorination in the medium of DMF revealed the diamagnetic Mo(VI) and paramagnetic Mo(V) complexes R2[MoOCl5], where R is [Me2NCOH2]+ (I) and [Me2NH2]+ (II). The hydrolysis of complex II gave Me2NH2Cl.
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27. 27
  Drobot, N. F.; Trifonova, E. N.; Krenev, V. A.; Drobot, D. V. Oxidative Dissolution of Refractory Metals by Chlorination in Aqueous Organic Media. Russ. J. Coord. Chem. 2005, 31, 243– 246, DOI: 10.1007/s11173-005-0084-4
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  Oxidative dissolution of refractory metals by chlorination in aqueous organic media
  Drobot, N. F.; Trifonova, E. N.; Krenev, V. A.; Drobot, D. V.
  Russian Journal of Coordination Chemistry (2005), 31 (4), 243-246CODEN: RJCCEY; ISSN:1070-3284. (Pleiades Publishing, Inc.)
  Chlorination of rhenium, tungsten, and molybdenum with gaseous chlorine in a DMF-water medium was studied. The degree to which the metals pass to the soln. is higher in the presence of water. The activating effect of water is attributed to the catalytic properties of solns. of HCl in DMF. The activating effect on metal dissoln. increases in the sequence W < Mo < Re.
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28. 28
  Drobot, N. F.; Kupriyanova, T. A.; Krenev, V. A.; Filippov, M. N. Rhenium and Platinum Recovery from Platinum and Rhenium Catalysts Used. Theor. Found. Chem. Eng. 2009, 43, 539– 543, DOI: 10.1134/S0040579509040319
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  Rhenium and platinum recovery from platinum and rhenium catalysts used
  Drobot, N. F.; Kupriyanova, T. A.; Krenev, V. A.; Filippov, M. N.
  Theoretical Foundations of Chemical Engineering (2009), 43 (4), 539-543CODEN: TFCEAU; ISSN:0040-5795. (Pleiades Publishing, Ltd.)
  The recovery of Re and Pt from spent Pt-Re catalysts is done by chlorinating with chlorine gas mixed with DMF and hydrochloric acid. The two-stage process conducted with a burning residue after the first phase chlorination results in addnl. platinum transfer into the soln. and makes it possible to obtain 70-94% platinum recovery and 91-96% rhenium recovery.
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  Chekmarev, A. M.; Buchikhin, E. P.; Sidorov, D. S.; Koshcheev, A. M. Zirconium Dissolution by Low-Temperature Chlorination in Dimethylformamide. Theor. Found. Chem. Eng. 2007, 41, 752– 754, DOI: 10.1134/S0040579507050521
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  Zirconium dissolution by low-temperature chlorination in dimethylformamide
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  The oxidative dissoln. of zirconium by low-temp. chlorination in N,N-dimethylformamide-chlorine-iron(III) chloride compns. has been studied. Optimum process parameters at low chlorine concns. have been detd. The orders of reaction in iron and chlorine have been detd. The activation energy of the process has been calcd.
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30. 30
  Buchikhin, E. P.; Kuznetsov, A. Y.; Vidanov, V. L.; Shatalov, V. V.; Chekmarev, A. M. Nonaqueous Chlorination of Uranium Metal in Tributyl Phosphate. Radiochemistry 2005, 47, 263– 265, DOI: 10.1007/s11137-005-0084-8
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  Nonaqueous Chlorination of Uranium Metal in Tributyl Phosphate
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  Low-temp. chlorination of uranium metal in the TBP-TCE-Cl2 systems was studied. Dissoln. of uranium in the dipolar aprotic solvent proceeds with formation of U(IV) compds. The activation energy of this process is 31.24 kJ mol-1, and relative reaction order with respect to Cl2 is 2. The effect of TBP concn. on chlorination was examd. The chlorination rate sharply increases at a water content in the TBP-TCE system of 0.2-0.6 vol %.
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31. 31
  Park, T. H.; Cho, Y. H.; Kang, B.; Kim, J. G.; Suh, K.; Kim, J.; Bae, S. E.; Kim, J. Y.; Giglio, J. J.; Jones, M. M. Constituent Analysis of Metal and Metal Oxide in Reduced SIMFuel Using Bromine-Ethyl Acetate. J. Radioanal. Nucl. Chem. 2018, 316, 1253– 1259, DOI: 10.1007/s10967-018-5841-1
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  Constituent analysis of metal and metal oxide in reduced SIMFuel using bromine-ethyl acetate
  Park, Tae-Hong; Cho, Young-Hwan; Kang, Byungman; Kim, Jong-Goo; Suh, Kyungwon; Kim, Jihye; Bae, Sang-Eun; Kim, Jong-Yun; Giglio, Jeffrey J.; Jones, Matthew M.
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  We demonstrated that bromine in Et acetate can selectively sep. metallic contents in lanthanide metal-oxide mixts. for anal., which had been validated for uranium. This Br2-EtOAc dissoln. method was applied to det. the constituents of metal and metal oxide in SIMFuel (simulated oxide spent fuel) that was electrochem. reduced from oxide fuel in the molten salt. Compared with the anal. results obtained after dissolving the fuel in an acid soln., we concluded that the Br2-EtOAc method can be applied to uranium and rare earths but not to noble metals for the redn. yield detn.
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  Cosstick, R. J.; Nancarrow, P. C. Estimation of Metallic Iron in Rusted Sponge-Iron: Dissolution of Iron Oxides by Bromine/Methanol. Talanta 1978, 25, 486– 488, DOI: 10.1016/0039-9140(78)80030-7
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  The soly. in Br-MeOH soln. of several Fe oxides commonly found in rusted sponge iron was examd. Oxide samples (10 mg, grain size <152 μ) were treated 20 min, and 2 h with 20 mL 5% Br-MeOH soln. at room temp. and under reflux. At room temp., <2.1% Fe dissolved, whereas 2 h reflux dissolved substantial amts. of Fe from samples of industrial mixed-oxides (9.92%), rust from steel (27.9%), and α-, β-, and γ-FeOOH (47.3, 52.9, and 41.6%, resp.), but <5% from Fe3O4, Fe2O3, and FeO samples.
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33. 33
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  Phase separation and analysis of sintered titanium carbide-nickel cermets using alcoholic bromine
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  (1961), 33 (), 1600-2CODEN: ANCHAM; ISSN:0003-2700.
  Sintered TiC was sepd. from TiC-Ni cermets by treating the sample with 5% Br in abs. MeOH for 6 hrs. at -20° and occasionally stirring with a thermometer. The soln. was filtered through a weighed fritted-glass crucible, and the ppt. was washed with abs. MeOH, dried at 110°, and weighed to obtain TiC.
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  Orefice, M.; Eldosouky, A.; Škulj, I.; Binnemans, K. Removal of Metallic Coatings from Rare-Earth Permanent Magnets by Solutions of Bromine in Organic Solvents. RSC Adv. 2019, 9, 14910– 14915, DOI: 10.1039/C9RA01696A
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  Removal of metallic coatings from rare-earth permanent magnets by solutions of bromine in organic solvents
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  RSC Advances (2019), 9 (26), 14910-14915CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
  Successful direct recycling routes are known for both Nd-Fe-B permanent magnets and Sm-Co permanent magnets. Often the magnets are coated by a nickel-copper-nickel coating to prevent corrosion of Nd-Fe-B magnets and chipping of Sm-Co magnets. However, this coating does not contribute to the magnetic properties and only ends up as a contamination in the recycled magnet powder, which in turn dils. the magnet alloy and reduces the magnetic performance. One soln. is the addn. of virgin magnet alloy to the recycled powder, but this is not the best option from a sustainable point of view. Another option is to remove the coating prior to the magnet recycling. We developed a solvometallurgical process for removal of the metallic coating prior to direct recycling. In particular, a mixt. of bromine in org. solvents was found to be very selective in the removal of the nickel-copper-nickel coating from both Nd-Fe-B permanent magnets and Sm-Co permanent magnets, without codissoln. of the magnet alloy.
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  A potential hazard in preparing bromine-methanol solutions
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  Journal of the Electrochemical Society (1990), 137 (4), 1309-11CODEN: JESOAN; ISSN:0013-4651.
  The reactivity of Br2-MeOH solns. useful in semiconductor etching and general chem. and biochem. prepns. was studied as a function of time and Br concn. 10-25 (vol./vol. %) mixts. all showed initial temp. increases followed by varying rates of temp. decrease. At higher Br concs., a second temp. increase occurred to reach the b.p. in the 25% soln. The study followed a violent explosion of a 50% vol./vol. soln. Some starting materials gave different temp. change patterns and an impurity may be involved.
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  Nakao, Y. Dissolution of Metals in Halogen-Cetylpyridinium Halide-Benzene Systems. J. Chem. Res., Synop. 1991, 228– 229
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  Dissolution of metals in halogen-cetylpyridinium halide-benzene systems
  Nakao, Yukimichi
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  Many metals can be dissolved in halogen-cetylpyridinium halide-benzene systems; linear rates of dissoln. of Fe, Ni, Cu, Zn, Pd, Ag and Au are reported.
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  Nakao, Y. Dissolution of Noble Metals in Halogen-Halide-Polar Organic Solvent Systems. J. Chem. Soc., Chem. Commun. 1992, 426– 427, DOI: 10.1039/C39920000426
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  Dissolution of noble metals in halogen-halide-polar organic solvent systems
  Nakao, Yukimichi
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  The dissoln. rates of Pd, Ag, and Au were detd. in (Cl, Br, I)-(Et4NCl, Me3NHCl, Et4NBr, KBr, KI, NaI)-(MeCN, MeOH, Me2CO) systems. The I-NaI-acetone system leached 99.3 Au and 93.5% Ag from an ore contg. 13.1 Au and 389.2 ppm Ag.
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  Nakao, Y. Three Procedures of Reversible Dissolution/Deposition of Gold Using Halogen-Containing Organic Systems. Chem. Commun. 1997, 1765– 1766, DOI: 10.1039/a704171c
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  Three procedures of reversible dissolution/deposition of gold using halogen-containing organic systems
  Nakao, Yukimichi
  Chemical Communications (Cambridge) (1997), (18), 1765-1766CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
  Gold is reversibly and repeatedly dissolved and deposited under restricted conditions in a soln. consisting of an elemental halogen, a halide and acetonitrile by a procedure involving one of three phys. operations: addn. of methanol, cooling, or evapn. to dryness.
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  Nakao, Y.; Sone, K. Reversible Dissolution/Deposition of Gold in Iodine-Iodide-Acetonitrile Systems. Chem. Commun. 1996, 897– 898, DOI: 10.1039/CC9960000897
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  Reversible dissolution/deposition of gold in iodine-iodide-acetonitrile systems
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  Chemical Communications (Cambridge) (1996), (8), 897-898CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
  Gold can be dissolved on heating in iodine-iodide-acetonitrile solvent systems, where the ratio I2/I- is >0.5, as [AuI2]-, and deposited from the resulting soln. on cooling via the formation of [AuI4]-.
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  Nakao, Y.; Kaeriyama, K. 5139752 Method for Extraction of Gold and Silver from Ore with a Solution Containing a Halogen, Halogenated Salt and Organic Solvent. Miner. Eng. 1993, 6, 438, DOI: 10.1016/0892-6875(93)90031-H
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  Nakao, Y.; Kaeriyama, K. Quaternary Ammonium Trihalide and Method for Dissolution of Metal with Liquid Containing the Compound. U.S. Patent 5,264,191, 1993.
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  Nakao, Y. Method for the Recovery of Gold Value. U.S. Patent 5,389,124, 1995.
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  Bricklebank, N.; Godfrey, S. M.; McAuliffe, C. A.; Pritchard, R. G. Facile One-Step Synthesis of the Cobalt(III) and Nickel(III) Tertiary Arsine Complexes [MI₃(AsMe₃)₂] (M = Co or Ni) Directly from the Powdered Elemental Metals. J. Chem. Soc., Dalton Trans. 1996, 157– 160, DOI: 10.1039/dt9960000157
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  Facile one-step synthesis of the cobalt(III) and nickel(III) tertiary arsine complex [MI3(AsMe3)2] (M = Co or Ni) directly from the powdered elemental metals
  Bricklebank, Neil; Godfrey, Stephen M.; McAuliffe, Charles A.; Pritchard, Robin G.
  Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry (1996), (2), 157-60CODEN: JCDTBI; ISSN:0300-9246. (Royal Society of Chemistry)
  Diiodotrimethylarsine, Me3AsI2, was treated with Co or Ni metal powder to give the metal(III) complex, [MI3(AsMe3)2]. In the case of Co, a metal(II) complex, [AsMe3I][CoI3(AsMe3)], was also produced, whereas for the Ni reaction only the Ni(III) complex, [NiI3(AsMe3)2], was formed in quant. yield. The only other product from the reactions was diiodine, which was detected spectrophotometrically. Both complexes were crystallog. characterized and are isostructural, consisting of a metal(III) atom with three equatorial iodide ligands capped by two trimethylarsine ligands. These complexes are unique examples of x-ray structural characterization of compds. of this stoichiometry. Conventional wisdom would not have expected the 'soft' ligands I- and AsMe3 to bind to the relatively hard metal(III) center.
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  Godfrey, S. M.; McAuliffe, C. A.; Pritchard, R. G. Inorganic Grignard Analogues. Reaction of Nickel Powder with Dihalogenotriorganophosphorus Compounds to Form Nickel-(II) and -(III) Phosphine Complexes; Isolation of Planar [Ni(PPh₃)I₃]⁻ and the Crystal Structure of [Ni(PPhMe₂)₂Br₂]. J. Chem. Soc., Dalton Trans. 1993, 2875– 2881, DOI: 10.1039/dt9930002875
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  Inorganic Grignard analogs. Reaction of nickel powder with dihalogenotriorganophosphorus compounds to form nickel-(II) and -(III) phosphine complexes; isolation of planar [Ni(PPh3)I3]- and the crystal structure of [Ni(PPhMe2)2Br2]
  Godfrey, Stephen M.; McAuliffe, Charles A.; Pritchard, Robin G.
  Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry (1972-1999) (1993), (19), 2875-81CODEN: JCDTBI; ISSN:0300-9246.
  Reactions of R3PX2 (R = Me, Et, Pr, Bu, Ph, PhCH2CH2; X = Br, I) with unactivated coarse-grain Ni metal powder were studied. The nature of the Ni phosphine complexes formed is dependent on both R and X. Where R ≠ Me and X = I [R3PI][Ni(PR3)I3] are formed, analogous to, but not isostructural with, similar Co complexes of the same stoichiometry formed from Co powder and R3PI2. Quant. electronic spectroscopic studies indicated that [R3PI][Ni(PR3)I3] all have predominantly square-planar geometry around Ni. When R = Me and X = I, [Ni(PMe3)2I3] is obtained in quant. yield, the other product being I2. Reaction of Ni powder with Me2PhPI2 yields both [Me2PhPI][Ni(PPhMe2)I3] and [Ni(PPhMe2)2I3]. These observations again mirror analogous Co reactions. Reaction of R3PBr2 with Ni powder is sensitive to the nature of R. Where R = Me, Et, or Pr no reaction occurs; where R3 = PhMe2 square-planar [Ni(PPhMe2)2Br2] and octahedral Ni(PPhMe2)2Br4 are obtained in equal yield. Where R3 = Ph2Pr octahedral [Ni(PPh2Pr)2Br4] is formed with a trace of square-planar [Ni(PPh2Pr)2Br2], and where R = Ph octahedral [Ni(PPh3)2Br4] is formed in quant. yield. [Ni(PPhMe2)2Br2] was crystallog. characterized: monoclinic, space group P21/a, a 10.018(2), b 10.249(1), c 10.138(1) Å, Z = 2, R = 0.061, R' = 0.069 (mol. centrosym.).
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46. 46
  Godfrey, S. M.; McAuliffe, C. A.; Pritchard, R. G. The Reaction of Bromo- and Iodo-Phosphoranes with Unactivated Coarse Grain Manganese Metal Powder to Yield [MnI₂(Phosphine)₂] and [{MnX₂(Phosphine)}_n] (X = Br or I) by Insertion of Mn into the P-X Bond. The Crystal Structure of [MnI₂(PPh₃)₂]. J. Chem. Soc., Dalton Trans. 1993, 371– 375, DOI: 10.1039/DT9930000371
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  The reaction of bromo- and iodo-phosphoranes with unactivated coarse grain manganese metal powder to yield [MnI2(phosphine)2] and [{MnX2(phosphine)}n] (X = Br or I) by insertion of Mn into the P-X bond. The crystal structure of [MnI2(PPh3)2]
  Godfrey, Stephen M.; McAuliffe, Charles A.; Pritchard, Robin G.
  Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry (1972-1999) (1993), (3), 371-5CODEN: JCDTBI; ISSN:0300-9246.
  The novel reaction of crude Mn metal powder with R3PX2 (X = Br, I) was studied. Reaction of R3PI2 (R = Ph or substituted aryl) with Mn allows insertion of Mn into P-I bonds and gives monomeric tetrahedral [MnI2(PR3)2] and MnI2. Reaction of R3PX2 (R3 = mixed aryl/alkyl, trialkyl; X = Br, I) with Mn, proceeded via insertion into P-X bonds, and leads to the quant. isolation of polymeric [{MnX2(PR3)}n], illustrating the subtle nature of these reactions. Examples of both types of complexes were crystallog. characterized and represent rare examples of such. There is some evidence that where R3 = Ph2Me an equil. exists and both types, [MnI2(PPh2Me)2] and [{MnI2(PPh2Me)}n], can be detected from the same reaction. Crystal data: [MnI2(PPh3)2]; monoclinic, space group P21/c, a 19.135(2), b 10.286(2), c 18.690(2) Å, Z = 4, R = 0.069, R' = 0.045.
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47. 47
  Godfrey, S. M.; McAuliffe, C. A.; Pritchard, R. G. Extreme Symbiosis: The Facile One-Step Synthesis of the Paramagnetic Cobalt(III) Complex of Triphenylantimony, Col₃(SbPh₃)₂, from the Reaction of Triphenylantimonydiiodine with Unactivated Coarse Grain Cobalt Metal Powder. J. Chem. Soc., Chem. Commun. 1994, 45– 46, DOI: 10.1039/c39940000045
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  Extreme symbiosis: the facile one-step synthesis of the paramagnetic cobalt(III) complex of triphenylantimony, CoI3(SbPh3)2, from the reaction of triphenylantimony diiodine with unactivated coarse grain cobalt metal powder
  Godfrey, Stephen M.; McAuliffe, Charles A.; Pritchard, Robin G.
  Journal of the Chemical Society, Chemical Communications (1994), (1), 45-6CODEN: JCCCAT; ISSN:0022-4936.
  Triphenylantimony diiodine (2 equiv.) reacts with unactivated cobalt powder to yield the unexpected cobalt(III) complex CoI3(SbPh3)2 (I); this five coordinate species represents a rare example of a paramagnetic cobalt(III) complex. The crystal structure of I was detd.
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48. 48
  Bricklebank, N.; Godfrey, S. M.; McAuliffe, C. A.; MacKie, A. G.; Pritchard, R. G. The X-Ray Crystal Structure of [Zn(PEt₃)I₂]₂, the First 1:1 Zinc(II) Complex of a Tertiary Phosphine of Low Steric Requirements, Prepared by the Reaction of Unactivated Zinc Metal with Diiodotriethylphosphorane. J. Chem. Soc., Chem. Commun. 1992, 944– 945, DOI: 10.1039/c39920000944
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  The x-ray crystal structure of [Zn(PEt3)I2]2, the first 1:1 zinc(II) complex of a tertiary phosphine of low steric requirements, prepared by the reaction of unactivated zinc metal with diiodotriethylphosphorane
  Bricklebank, Neil; Godfrey, Stephen M.; McAuliffe, Charles A.; Mackie, Anthony G.; Pritchard, Robin G.
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  Pd dissoln. capabilities of a variety of org. triiodides (OrgI3) in org. solvent, where Org+ =3,5-bis(phenylamino)-1,2-dithiolylium [(PhHN)2DTL+], 3,5-bis(morpholino)-1,2-dithiolylium (Mo2DTL+); tetrabuthylammonium (TBA+); and tetraphenylphosphonium (Ph4P+), toward the crude metal and model-spent 3-way catalyst (TWC), are described here. Enhanced Pd-leaching yields from TWC were obtained using OrgI3 solns. (≤98%) in spite of the fully inorg. KI3 one (38%) in the same mild conditions. The reaction products were isolated and characterized as Org2[Pd2I6]. Crystallog. and DFT studies highlighted the presence of several ion-pair secondary interactions in the products, which can explain the improved effectiveness of the Pd etching by OrgI3. For comparison purposes, the gold leaching by using R2DTLI3 and the obtained Au complexes were studied. Preliminary results addressed to recover the metal and the reagents from the etching product showed that (PhHN)2DTLI3 is the most promising reagent to improve sustainability in the whole process.
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  Serpe, A.; Artizzu, F.; Mercuri, M. L.; Pilia, L.; Deplano, P. Charge Transfer Complexes of Dithioxamides with Dihalogens as Powerful Reagents in the Dissolution of Noble Metals. Coord. Chem. Rev. 2008, 252, 1200– 1212, DOI: 10.1016/j.ccr.2008.01.024

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Oxidative Dissolution of Metals in Organic Solvents

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1. Introduction

Figure 1

Figure 2

2. Solutions of Halogens in Polar Organic Solvents

2.1. Halogens in Organic Solvents

2.1.1. Bromine in Organic Solvents

Figure 3

2.1.2. Chlorine in Organic Solvents

Scheme 1

Figure 4

Scheme 2

2.1.3. Other Halogens in Organic Solvents

2.2. Halogens + Halide Ligands + Organic Solvents

2.3. Dihalogen or Interhalogen Adducts

Scheme 3

Scheme 4

Scheme 5

Figure 5

Scheme 6

Scheme 7

Figure 6

Scheme 8

Figure 7

3. Halocarbons as Oxidizing Agent

Figure 8

Scheme 9

4. Donor–Acceptor Electron-Transfer Systems

4.1. DMSO with Halide Acids or Salts

Scheme 10

Scheme 11

Scheme 12

4.2. DMSO with SO2

4.3. Organic Aqua Regia

Figure 9

5. Ionic Liquids and Deep Eutectic Solvents

5.1. Ionic Liquids

5.1.1. ILs as Oxidizing Agents

Scheme 13

5.1.2. ILs as Solvents

Figure 10

5.2. Deep-Eutectic Solvents

6. Other Oxidizing Agents

6.1. Oxygen Gas

Scheme 14

Figure 11

6.2. Nitrogen Dioxide

6.3. Copper(II) Bromide

6.4. Organic Compounds

Scheme 15

7. Conclusions and Outlook

Author Information

Biographies

Xiaohua Li

Koen Binnemans

Acknowledgments

Abbreviations

References

Cited By

Abstract

Figure 1

Figure 2

Figure 3

Scheme 1

Figure 4

Scheme 2

Scheme 3

Scheme 4

Scheme 5

4.2. DMSO with SO₂