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Transesterification of Methyl-10-undecenoate and Poly(ethylene adipate) Catalyzed by (Cyclopentadienyl)titanium Trichlorides as Model Chemical Conversions of Plant Oils and Acid-, Base-Free Chemical Recycling of Aliphatic Polyesters

Cite this: ACS Sustainable Chem. Eng. 2022, 10, 38, 12504–12509
Publication Date (Web):September 15, 2022
https://doi.org/10.1021/acssuschemeng.2c04877

Copyright © 2022 The Authors. Published by American Chemical Society. This publication is licensed under

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Supporting Info (1)»

Abstract

Highly active and exclusive transesterifications of methyl 10-undecenoate with alcohols (cyclohexanemethanol, 1,4-cyclohexanedimethanol, 10-undecen-1-ol, 3-hexanol) have been demonstrated by Cp′TiCl3 (Cp′ = Cp, C5Me5) at 100–120 °C. The CpTiCl3 enabled depolymerization of poly(ethylene adipate) by the transesterification (>99% conv., 0.25–0.5 mol % Ti) at 120 °C; the depolymerization completed after 6 h at 150 °C (0.5 mol % Ti).

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Synopsis

Efficient transesterifications of methyl 10-undecenoate (FAEs) and depolymerization (chemical recycle) of polyesters with alcohols have been demonstrated by CpTiCl3.

Introduction

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The efficient chemical conversion of plant oils [fatty acids and the esters (FAEs)] to biofuels, (1−5) aliphatic polyesters, (6−13) and fine chemicals (6−8,14,15) has been an important subject for development of the alternative technology of petroleum-based process. The catalytic transesterification has been recognized as the key reaction for the purpose. (5,15−31) Moreover, acid-, base-free depolymerization of polyesters to monomers (efficient chemical recycling under mild conditions) has also been considered as one of the key subjects to establish the circular economy. (32−34) Since there are also the reports concerning the catalysis for organic synthesis, (35−37) we thus first revisited the catalyst screening to find the suitable catalysts for the transesterification of biobased FAEs and applied them to the depolymerization of aliphatic polyesters by reaction with alcohols.
We herein communicate that an efficient transesterification of unsaturated fatty acid ester, methyl 10-undecenoate (MU), with alcohols has been demonstrated by CpTiCl3 and Cp*TiCl3 (Cp* = C5Me5); CpTiCl3 also enabled depolymerization of aliphatic polyesters, poly(ethylene adipate) (PEA) and poly(butylene adipate) (PBA), and chemical recycling to monomers (Scheme 1).

Scheme 1

Scheme 1. Catalytic Transesterification of Methyl-1-undecenoate (MU) and Poly(ethylene adipate) (PEA)

Results and Discussion

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Transesterification of methyl 10-undenenoate (MU, derived from castor oil) with cyclohexanemethanol (CM, chosen for synthesis of 1,ω-diene by reaction with 1,4-cyclohexanedimethanol, monomer in biobased aliphatic polyester (9,27,39)) has been chosen as a model reaction for the catalyst screening (chosen from previous reports for fine chemicals synthesis, (35−37) Lewis acids). The reactions were conducted at 100 °C in the presence of a minimum amount of solvent (toluene) to charge the catalyst (0.5 mol %). The selected results are summarized in Table 1, and the additional results are also shown in the Supporting Information, Table S1. (38)
Table 1. Transesterification of Methyl-10-undecenoate with Cyclohexanemethanol (Catalyst 0.5 mol %, 100 °C)a
runcatalysttime (h)yieldb (%)select.b (%)TONc
1Sc(OTf)33369372
2Sc(OTf)3247379146
312MoO3·H3PO4·xH2O36394126
412MoO3·H3PO4·xH2O24445288
5Ti(OiPr)433.7197
6TiCl4(THF)2376>99152
7TiCl4(THF)2247779154
8CpTiCl3360>99120
9CpTiCl3674>99148
10CpTiCl32490>99180
11dCpTiCl3392>99184
12Cp*TiCl3359>99118
13Cp*TiCl3680>99160
14Cp*TiCl3248295164
15dCp*TiCl3392>99184
16Cp2TiCl235388106
17Hf(OTf)436378126
18Hf(OTf)4245866116
19FeCl3338>9976
20FeCl3655>99110
21FeCl3248295164
22FeBr3332>9964
23FeBr366398126
24FeBr3248391166
a

Conditions: Methyl-10-undecenoate (MU) and cyclohexanemethanol (CM) 2.0 mmol (MU:CM = 1.0:1.0 molar ratio), catalyst 0.5 mol %, toluene 0.5 mL, 100 °C.

b

Based on MU; selectivity (%) = (molar amount of 1 formed/molar amount of MU reacted) × 100.

c

TON (turnover number) = product (mmol)/catalyst (mmol). TON based on Mo (runs 3 and 4).

d

Temp. 120 °C.

It was revealed that Sc(OTf)3 (OTf = CF3SO3) and Hf(OTf)4, known as the efficient catalysts, (35,36) showed the rather low selectivity especially after long reaction hours (runs 2 and 18, observed as an additional peak in the GC chromatograms, exemplified as Figure S14), (38) suggesting a possibility of the occurrence of a side reaction from the product, cyclohexymethyl-10-undecenoate (1). Similar trends were observed in the reactions with TiCl4(THF)2 and phosphomolybdic acid, 12MoO3·H3PO4·xH2O, as the catalysts (runs 4 and 7), whereas TiCl4(THF)2 exhibited both high activity and selectivity at 120 °C after 3 h (run S6, Table S1). (38) In contrast, the reactions by FeCl3 and FeBr3 proceeded with high selectivities (runs 19–24) and significant decreases in the selectivity were not seen even after long reaction hours (runs 21 and 24); the activity slightly increased at 120 °C (run S8, Table S1). (38) The attempted reactions in the presence of V(acac)3 (acac = acetylacenonato), Mn(CH3CO2)2, Ru(acac)3, Ni(acac)2, NiCl2, Cu[CF3C(O)CHC(O)CF3]2, Cu(OTf)2, Zn(CH3CO2)2, CeCl3, nBu4N+X (X = Br, I, HSO4), and Ph3(Me)P+X (X = Br, I) conducted under the same conditions (0.5 mol %, 100 °C, 3 h) recovered the starting compounds.
It should be noted that CpTiCl3 and Cp*TiCl3 exhibited higher catalytic activities (TON 120 and 118, respectively, after 3 h at 100 °C, runs 8 and 12), and the reaction proceeded with high selectivity even after 24 h (runs 10 and 14). Moreover, the reactions at 120 °C afforded the corresponding ester (1) exclusively (selectivity >99%) in high yields (92%, runs 11 and 15). The presence of chloride in the ligand seems important for exhibiting the high activity, because Ti(OiPr)4 and Cp*TiMe2(O-2,6-Me2C6H3) showed the low activities (run 7 and run S11). In contrast, Cp2TiCl2 and Cp*TiCl2(Y) (Y = O-2,4,6-Me3C6H2, O-2,6-Cl2-4-MeC6H2, N═CtBu2), (indenyl)TiCl2(N═CtBu2), and (tBuC5H4)TiCl2(O-2,6-tBu2-4-MeC6H2) showed moderate activities (runs 16 and S9–S14), (38) although the observed activities were rather low compared to those by CpTiCl3 and Cp*TiCl3 conducted under the same conditions. Therefore, the trichlorides seem more suited for this purpose as the titanium catalysts.
On the basis of the initial catalyst screening, the reactions with CpTiCl3, Cp*TiCl3, FeCl3, and FeBr3 were further explored as summarized in Table 2. Additional results are shown in Table S2 in the Supporting Information. (38) Interestingly, the activities increased when the reactions by FeCl3 and FeBr3 were conducted under low catalyst concentration conditions with preservation of the high selectivities (runs 25–28, S15, and S16); the TON by FeCl3 reached 292, affording 1 in 73% yield as the exclusive product (run 26).
Table 2. Transesterification of Methyl-10-undecenoate (MU) with Cyclohexanemethanol by FeCl3, FeBr3, CpTiCl3, and Cp*TiCl3 at 100 °C (Effect of Time Course and Catalyst Concentrationa)
runcatalystMU (mmol)time (h)yieldb (%)select.c (%)TONd
19FeCl32.0655>99110
25FeCl34.0644>99176
26FeCl34.02473>99292
22FeBr32.066398126
27FeBr34.0642>99168
28FeBr34.02460>99240
8CpTiCl32.0674>99148
29CpTiCl34.0332>99128
30CpTiCl34.0666>99264
31CpTiCl34.02485>99340
12Cp*TiCl32.0680>99160
32Cp*TiCl34.0359>99118
33Cp*TiCl34.0664>99256
34Cp*TiCl34.02481>99324
a

Conditions: catalyst 0.01 mmol (0.25 or 0.5 mol %), methyl-10-undecenoate (MU) and cyclohexanemethanol (CM) 2.0 or 4.0 mmol (MU:CM = 1.0:1.0 molar ratio), toluene 0.5 mL.

b

Based on MU.

c

Selectivity (%) = (1 formed in mmol/MU reacted in mmol) × 100.

d

TON = product (mmol)/catalyst (mmol).

Similarly, the activities by CpTiCl3 and Cp*TiCl3 increased upon increasing the reaction scale with lowering the catalyst concentration. It thus seems likely that the increase of activity (especially after 6 h) could be explained as being due to the fact that the reaction would be (first order) dependent upon the substrate (MU) concentration in situ (although we have not yet conducted it in detail). The reaction after 24 h exclusively gave 1 in high yields (85 and 81% for runs 31 and 34). In contrast, improvements in the selectivities after 24 h were not observed when the reactions by Sc(OTf)3, Hf(OTf)4, and TiCl4(THF)2 were also conducted under the same conditions (Table S2). (38) Therefore, further studies were conducted in the presence of CpTiCl3 (and Cp*TiCl3).
As shown in Table 3, Cp′TiCl3 (Cp′ = Cp, Cp*) are also effective catalysts for transesterification of MU with 1,4-cyclohexanedimethanol to afford the monoester (3, as the initial product) and diester (2) exclusively. (38) The activities conducted at 120 °C were apparently higher than those conducted at 100 °C. Noteworthy is that the quantitative conversions (both >99% conversions and the yields) of MU to the diester (2), a monomer for synthesis of biobased aliphatic polyester, (9,39) could be demonstrated in the reaction by CpTiCl3 at 120 °C (run 37).
Table 3. Transesterification of Methyl-10-undecenoate (MU) with 1,4-Cyclohexanedimethanol (CD)a
     yieldb (%)select.c
runcatalyst (mol %)temp. (°C)time (h)conv.b (%)322 + 3(2 + 3)
35CpTiCl3 (0.5)100249722699194
36CpTiCl3 (0.5)12018>99595100>99
37CpTiCl3 (0.5)12024>99 99100>99
38Cp*TiCl3 (0.5)100249725669194
39Cp*TiCl3 (1.0)1002496375996>99
40Cp*TiCl3 (0.5)12018>99496100>99
a

Conditions: catalyst 0.01 mmol (0.5 or 1.0 mol % Ti to MU), methyl-10-undecenoate (MU) 2.0 mmol (1.0 mmol, run 39), MU:CD = 2.0:1.0 molar ratio; 1,4-cyclohexanedimethanol (CD), toluene 0.5 mL.

b

Based on CD.

c

Selectivity on the basis of MU.

Moreover, as shown in Scheme 2, CpTiCl3 catalyzed transesterifications of MU with 10-undecen-1-ol to give undec-10-enyl undec-10-enoate exclusively (>99% selectivity), also used as monomer for the polyester. (40,41) The quantitative conversion of MU could also be demonstrated when the reaction was conducted at 120 °C after 12 h (0.5 mol %, TON 200). The reaction with 3-hexanol (as a model of secondary alcohol) at 120 °C also gave the product with the exclusive selectivity (84% yield after 18 h). (38)

Scheme 2

Scheme 2. Transesterification of Methyl-10-undecenoate (MU) with 10-Undecen-1-ol and 3-Hexanol (38)
It has been postulated that activation of the carbonyl group in the ester by coordination to the titanium (as a Lewis acid) could play a role in this catalysis. However, as shown in Figures S41–S45, no significant differences in the resonance corresponding to the carbonyl carbon in MU were observed upon addition of CpTiCl3 (1.0 equiv) in CDCl3; no significant differences in the carbonyl carbon were seen in the CDCl3 solution containing CpTiCl3 upon addition of MU (1.0 equiv) and CM (1.0 or 1.5 equiv).
In contrast, as shown in Figure 1, (42) a decrease in the (so-called) shoulder edge peak ascribed to the Ti–Cl absorption (4978.5 eV, shown as an arrow) (43,44) in the Ti K-edge XANES (X-ray absorption near edge structure) spectra was observed when MU (50 and 100 equiv) was added to CpTiCl3 in toluene at 25 °C, whereas no significant changes were observed in the edge absorption (strongly suggesting the preservation of the oxidation state) and the pre-edge absorptions (observed at 4966.5 and 4967.9 eV in CpTiCl3). Slight changes in the pre-edge absorptions with their intensities were observed at 4966.7 and 4967.9 eV when CM (50 equiv) was added to CpTiCl3 in toluene; the spectrum was the same when both MU and CM were added to CpTiCl3 in toluene. These results suggest that the geometry around titanium would change especially upon addition of CM with preservation of the oxidation state. (45)

Figure 1

Figure 1. Ti K-edge XANES spectra (in toluene at 25 °C) for CpTiCl3 upon addition of methyl 10-undecenoate (MU, 50 or 100 equiv) and/or cyclohexanemethanol (CM 50 equiv). (42)

Based on the EXAFS (extended X-ray absorption fine structure) analysis of these spectra (shown in Figures S35–S39, and the analysis data for the coordination numbers and the bond distances are summarized in Table S3), it was revealed that one Cl in CpTiCl3 was replaced with an oxygen atom (1.75–1.79 Å, σ bond character) upon addition of MU or CM. Partial formation of one Ti–O σ bond would also be suggested by monitoring the NMR spectra in the reaction of CpTiCl3 with 1.0 equiv of CM as well as with MU and CM (in CDCl3, Figures S44–S47). (45−48) In addition to the XANES analysis data, it is thus strongly suggested that formation of ester or alcohol coordinated species plays a role in this catalysis. It thus seems likely that the presence of a Ti–Cl bond would be necessary to activate the substrate. (49)
It should be noted that transesterification of poly(ethylene adipate) (PEA) with CM by CpTiCl3 (0.25 or 0.5 mol %) completed after 18 h at 120 °C (Scheme 3). (38) The reaction product was bis(cyclohexylmethyl)adipate exclusively accompanied with formation of ethylene glycol (EG). Monitoring the reaction by 13C NMR spectra (Figure S23, Supporting Information) revealed that the resonance corresponding to the carbonyl carbon (173.0 ppm) in PEA already disappeared even after 1 h (Figure S23c) and the intensity of a new resonance at 173.4 ppm corresponding to carbonyl carbon of the diester increased gradually and became a sole resonance after 18 h (Figure S23h and Figure S24f), (38) strongly suggesting the proceeding of this depolymerization. The products were confirmed not only by NMR spectra but also by the GC chromatograms (quantitative analysis using an internal standard). (38) The transesterification completed even in the presence of 0.25 mol % of CpTiCl3 (120 °C, 18 h, corresponding to TON 800 on the basis of ester formation). (38)

Scheme 3

Scheme 3. Depolymerization of Poly(ethylene adipate) (PEA) by Transesterification with Cyclohexanemethanol (CM) (38)
Moreover, importantly, transesterification of PEA (500 mg) with ethanol (5.0 mL) by CpTiCl3 (1.0 mol %) at 120 °C completed after 24 h to afford diethyl adipate (yield >99% GC) and EG. Note that the reaction by CpTiCl3 (0.5 or 1.0 mol %) completed even after 6 h at 150 °C (Scheme 3). (38) The transesterification of poly(butylene adipate) (PBA) (500 mg) with ethanol (5.0 mL) by CpTiCl3 (1.0 mol %) also completed after 3 h at 150 °C, affording dibutyl adipate (yield >99%) and 1,4-butanediol exclusively (by GC and 13C NMR spectra). (38)

Conclusion

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We have shown that CpTiCl3 and Cp*TiCl3 exhibited promising capability of selective transesterification of FAE (exemplified by MU) with alcohols (CM, 1,4-cyclohexanedimethanol, 10-undecen-1-ol, 3-hexanol) at 100 °C and the activity increased at 120 °C. CpTiCl3 catalyzed depolymerization of PEA and PBA by the transesterification with alcohols (CM and ethanol) at 120–150 °C. On the basis of solution XAS (XANES and EXAFS) analysis, one Ti–Cl bond in CpTiCl3 was replaced with a Ti–O bond (1.75–1.79 Å, with a Cp–Ti bond and two Ti–Cl bonds remaining) upon addition of MU or CM without a change in Ti(IV) oxidation state. The present catalyst demonstrates an acid-, base-free depolymerization of aliphatic polyesters under rather mild conditions. We shall introduce more results in the forthcoming articles.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acssuschemeng.2c04877.

  • General procedure, calculations for reaction products by GC and synthesis of standards, additional results in the transesterification of methyl-10-undecenoate (MU) with cyclohexanemethanol (CM) and the selected GC charts, depolymerization results, Ti K-edge XANES spectra for the catalyst solution and their EXAFS analysis data, and 13C NMR spectra for CpTiCl3 upon addition of MU and/or CM (PDF)

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Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

Author Information

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  • Corresponding Author
  • Authors
    • Tomoyuki Aoki - Department of Chemistry, Tokyo Metropolitan University, 1-1 Minami Osawa, Hachioji, Tokyo 192-0397, Japan
    • Yuriko Ohki - Department of Chemistry, Tokyo Metropolitan University, 1-1 Minami Osawa, Hachioji, Tokyo 192-0397, Japan
    • Soichi Kikkawa - Department of Chemistry, Tokyo Metropolitan University, 1-1 Minami Osawa, Hachioji, Tokyo 192-0397, JapanOrcidhttps://orcid.org/0000-0002-8193-6374
    • Seiji Yamazoe - Department of Chemistry, Tokyo Metropolitan University, 1-1 Minami Osawa, Hachioji, Tokyo 192-0397, JapanOrcidhttps://orcid.org/0000-0002-8382-8078
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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This project was partly supported by JST-CREST (Grant Number JPMJCR21L5), JST SICORP (Grant Number JPMJSC19E2), Japan, and Tokyo Metropolitan Government Advanced Research (Grant Number R2-1). XAS analysis was partly supported by Fund for the Promotion of Joint International Research (Fostering Joint International Research, 19KK0139). The authors express their thanks to Ms. N. Nakashima, Mr. M. Okabe, Mr. R. Iwase, Ms. M. Unoki, and Mr. K. Morishima (Tokyo Metropolitan Univ., TMU) for technical assistance for the XAS analysis at the BL01B1 beamline at the SPring-8 facility of Japan Synchrotron Radiation Research Institute (JASRI, proposal no. 2021B1594). K.N. and T.A. also express their thanks to Dr. S. M. A. H. Siddiki, Dr. Y. Ogiwara, Ms. S. Sudhakaran, and Mr. T. Fujioka (TMU) for technical assistance.

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    Malavolti, M.; Brandi, A.; Salvini, A.; Giomi, D. Transesterification of castor oil with trimethylchlorosilane: simultaneous formation of fatty acid alkyl esters and α-monochlorohydrin. RSC Adv. 2015, 5, 7734177347,  DOI: 10.1039/C5RA12756D
  26. 26
    Stanley, N.; Chenal, T.; Jacquel, N.; Saint-Loup, R.; Prates Ramalho, J. P.; Zinck, P. Organocatalysts for the synthesis of poly(ethylene terephthalate-co-isosorbide terephthalate): A combined experimental and DFT study. Macromol. Mater. Eng. 2019, 304, 1900298,  DOI: 10.1002/mame.201900298
  27. 27
    Sudhakaran, S.; Taketoshi, A.; Siddiki, S. M. A. H.; Murayama, T.; Nomura, K. Transesterification of ethyl-10-undecenoate using Cu deposited V2O5 catalyst as a model reaction for efficient conversion of plant oils to monomers, fine chemicals. ACS Omega 2022, 7, 43724380,  DOI: 10.1021/acsomega.1c06157
  28. 28
    For selected reports of monomer synthesis by transesterification, see refs :Fokou, P. A.; Meier, M. A. R. Use of a renewable and degradable monomer to study the temperature-dependent olefin isomerization during ADMET polymerizations. J. Am. Chem. Soc. 2009, 131, 16641665,  DOI: 10.1021/ja808679w
  29. 29
    Lillie, L. M.; Tolman, W. B.; Reineke, T. M. Structure/property relationships in copolymers comprising renewable isosorbide, glucarodilactone, and 2,5-bis(hydroxymethyl)furan subunits. Polym. Chem. 2017, 8, 37463754,  DOI: 10.1039/C7PY00575J
  30. 30
    Dannecker, P.-K.; Biermann, U.; Sink, A.; Bloesser, F. R.; Metzger, J. O.; Meier, M. A. R. Fatty acid-derived aliphatic long chain polyethers by a combination of catalytic ester reduction and ADMET or thiol-ene polymerization. Macromol. Chem. Phys. 2019, 220, 1800440,  DOI: 10.1002/macp.201800440
  31. 31
    Piccini, M.; Leak, D. J.; Chuck, C. J.; Buchard, A. Polymers from sugars and unsaturated fatty acids: ADMET polymerisation of monomers derived from D-xylose, D-mannose and castor oil. Polym. Chem. 2020, 11, 26812691,  DOI: 10.1039/C9PY01809C
  32. 32
    Coates, G. W.; Getzler, Y. D. Y. L. Chemical recycling to monomer for an ideal, circular polymer economy. Nat. Rev. Mater. 2020, 5, 501516,  DOI: 10.1038/s41578-020-0190-4
  33. 33
    Circular Economy of Polymers: Topics in Recycling Technologies; Collias, D. I., James, M. I., Layman, J. M., Eds.; ACS Symposium Series; American Chemical Society: Washington, DC, 2021. DOI: 10.1021/bk-2021-1391 .
  34. 34
    Häußler, M.; Eck, M.; Rothauer, D.; Mecking, S. Closed-loop recycling of polyethylene-like materials. Nature 2021, 590, 423427,  DOI: 10.1038/s41586-020-03149-9
  35. 35
    For selected reports of transesterification including long chain aliphatic esters, see refs :Ishihara, K.; Ohara, S.; Yamamoto, H. Science 2000, 290, 11401142,  DOI: 10.1126/science.290.5494.1140
  36. 36
    Ishihara, K.; Nakayama, M.; Ohara, S.; Yamamoto, H. Direct ester condensation from a 1:1 mixture of carboxylic acids and alcohols catalyzed by hafnium(IV) or zirconium(IV) salts. Tetrahedron 2002, 58, 8179,  DOI: 10.1016/S0040-4020(02)00966-3
  37. 37
    Hatano, M.; Ishihara, K. Lanthanum(III) catalysts for highly efficient and chemoselective transesterification. Chem. Commun. 2013, 49, 19831997,  DOI: 10.1039/c2cc38204k
  38. 38

    Additional results (the transesterification of MU with CM, the selected GC charts and the identifications, and the depolymerization results) are shown in the Supporting Information.

  39. 39
    Nomura, K.; Chaijaroen, P.; Abdellatif, M. M. Synthesis of biobased long-chain polyesters by acyclic diene metathesis polymerization and tandem hydrogenation and depolymerization with ethylene. ACS Omega 2020, 5, 1830118312,  DOI: 10.1021/acsomega.0c01965
  40. 40
    Rybak, A.; Meier, M. A. R. Acyclic diene metathesis with a monomer from renewable resources: Control of molecular weight and one-step preparation of block copolymers. ChemSusChem 2008, 1, 542547,  DOI: 10.1002/cssc.200800047
  41. 41
    Ortmann, P.; Mecking, S. Long-spaced aliphatic polyesters. Macromolecules 2013, 46, 72137218,  DOI: 10.1021/ma401305u
  42. 42

    The results including Ti K-edge (in toluene at 25 °C) EXAFS oscillations, FT-EXAFS spectra, and fitting curves and summary of analysis data are shown in the SI.

  43. 43
    Yi, J.; Nakatani, N.; Nomura, K.; Hada, M. Time-dependent DFT study of K-edge spectra for vanadium and titanium complexes: Effects of chloride ligands on pre-edge features. Phys. Chem. Chem. Phys. 2020, 22, 674682,  DOI: 10.1039/C9CP05891E
  44. 44
    Yi, J.; Nakatani, N.; Nomura, K. Solution XANES and EXAFS analysis of active species of titanium, vanadium complex catalysts in ethylene polymerisation/dimerisation and syndiospecific styrene polymerization. Dalton Trans. 2020, 49, 80088028,  DOI: 10.1039/D0DT01139H
  45. 45

    On the basis of EXAFS analysis, formation of the mono alkoxide CpTiCl2(OCH2C6H11) would be suggested, and further reaction did not proceed under these conditions (as expected from the reported results described in refs (46−48), shown below). NMR spectra are shown in the Supporting Information.

  46. 46
    For the reaction of CpTiCl3 with alcohols and phenol, see refs :Hafner, A.; Duthaler, R. O.; Marti, R.; Rihs, G.; Rothe-Streit, P.; Schwarzenbach, F. Enantioselective syntheses with titanium carbohydrate complexes. Part 7. Enantioselective allyltitanation of aldehydes with cyclopentadienyldialkoxyallyltitanium complexes. J. Am. Chem. Soc. 1992, 114, 23212336,  DOI: 10.1021/ja00033a005
  47. 47
    Nomura, K.; Naga, N.; Miki, M.; Yanagi, K. Olefin polymerization by (cyclopentadienyl)(aryloxy)titanium(IV) complexes-cocatalyst systems. Macromolecules 1998, 31, 75887597,  DOI: 10.1021/ma980690f
  48. 48
    Zhao, W.; Yan, Q.; Tsutsumi, K.; Nomura, K. Efficient norbornene (NBE) incorporation in ethylene/NBE copolymerization by half-titanocene catalysts containing chlorinated aryloxo ligands. Organometallics 2016, 35, 18951905,  DOI: 10.1021/acs.organomet.6b00242
  49. 49

    Reviewers commented that HCl plays a role in this catalysis. (46) However, this can be excluded due to low selectivity in the reaction with TiCl4(THF)2 under the same conditions (Table 1 and Table S1 in the Supporting Information). We have added depolymerization results (PEA 500 mg, 1.0 mol% CpTiCl3, EtOH 5.0 mL, 150 °C 6 h) after placing the premixed solution of CpTiCl3 and EtOH in vacuo (to remove volatile) in the Supporting Information (Figures S48 and S49). We confirmed completion of the depolymerization to yield diethyl adipate and EG.

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This article is cited by 4 publications.

  1. Yohei Ogiwara, Kotohiro Nomura. Chemical Upcycling of PET into a Morpholine Amide as a Versatile Synthetic Building Block. ACS Organic & Inorganic Au 2023, 3 (6) , 377-383. https://doi.org/10.1021/acsorginorgau.3c00037
  2. Mika Kojima, Xiuxiu Wang, Lance O’Hari P. Go, Ryoji Makino, Yuichi Matsumoto, Daisuke Shimoyama, Mohamed Mehawed Abdellatif, Joji Kadota, Seiji Higashi, Hiroshi Hirano, Kotohiro Nomura. Synthesis of High Molecular Weight Biobased Aliphatic Polyesters Exhibiting Tensile Properties Beyond Polyethylene. ACS Macro Letters 2023, 12 (10) , 1403-1408. https://doi.org/10.1021/acsmacrolett.3c00481
  3. Xiuxiu Wang, Weizhen Zhao, Kotohiro Nomura. Synthesis of High-Molecular-Weight Biobased Aliphatic Polyesters by Acyclic Diene Metathesis Polymerization in Ionic Liquids. ACS Omega 2023, 8 (7) , 7222-7233. https://doi.org/10.1021/acsomega.3c00390
  4. Yuriko Ohki, Yohei Ogiwara, Kotohiro Nomura. Depolymerization of Polyesters by Transesterification with Ethanol Using (Cyclopentadienyl)titanium Trichlorides. Catalysts 2023, 13 (2) , 421. https://doi.org/10.3390/catal13020421
  • Abstract

    Scheme 1

    Scheme 1. Catalytic Transesterification of Methyl-1-undecenoate (MU) and Poly(ethylene adipate) (PEA)

    Scheme 2

    Scheme 2. Transesterification of Methyl-10-undecenoate (MU) with 10-Undecen-1-ol and 3-Hexanol (38)

    Figure 1

    Figure 1. Ti K-edge XANES spectra (in toluene at 25 °C) for CpTiCl3 upon addition of methyl 10-undecenoate (MU, 50 or 100 equiv) and/or cyclohexanemethanol (CM 50 equiv). (42)

    Scheme 3

    Scheme 3. Depolymerization of Poly(ethylene adipate) (PEA) by Transesterification with Cyclohexanemethanol (CM) (38)
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      Malavolti, M.; Brandi, A.; Salvini, A.; Giomi, D. Transesterification of castor oil with trimethylchlorosilane: simultaneous formation of fatty acid alkyl esters and α-monochlorohydrin. RSC Adv. 2015, 5, 7734177347,  DOI: 10.1039/C5RA12756D
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      Stanley, N.; Chenal, T.; Jacquel, N.; Saint-Loup, R.; Prates Ramalho, J. P.; Zinck, P. Organocatalysts for the synthesis of poly(ethylene terephthalate-co-isosorbide terephthalate): A combined experimental and DFT study. Macromol. Mater. Eng. 2019, 304, 1900298,  DOI: 10.1002/mame.201900298
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      Sudhakaran, S.; Taketoshi, A.; Siddiki, S. M. A. H.; Murayama, T.; Nomura, K. Transesterification of ethyl-10-undecenoate using Cu deposited V2O5 catalyst as a model reaction for efficient conversion of plant oils to monomers, fine chemicals. ACS Omega 2022, 7, 43724380,  DOI: 10.1021/acsomega.1c06157
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      Dannecker, P.-K.; Biermann, U.; Sink, A.; Bloesser, F. R.; Metzger, J. O.; Meier, M. A. R. Fatty acid-derived aliphatic long chain polyethers by a combination of catalytic ester reduction and ADMET or thiol-ene polymerization. Macromol. Chem. Phys. 2019, 220, 1800440,  DOI: 10.1002/macp.201800440
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    36. 36
      Ishihara, K.; Nakayama, M.; Ohara, S.; Yamamoto, H. Direct ester condensation from a 1:1 mixture of carboxylic acids and alcohols catalyzed by hafnium(IV) or zirconium(IV) salts. Tetrahedron 2002, 58, 8179,  DOI: 10.1016/S0040-4020(02)00966-3
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    38. 38

      Additional results (the transesterification of MU with CM, the selected GC charts and the identifications, and the depolymerization results) are shown in the Supporting Information.

    39. 39
      Nomura, K.; Chaijaroen, P.; Abdellatif, M. M. Synthesis of biobased long-chain polyesters by acyclic diene metathesis polymerization and tandem hydrogenation and depolymerization with ethylene. ACS Omega 2020, 5, 1830118312,  DOI: 10.1021/acsomega.0c01965
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    41. 41
      Ortmann, P.; Mecking, S. Long-spaced aliphatic polyesters. Macromolecules 2013, 46, 72137218,  DOI: 10.1021/ma401305u
    42. 42

      The results including Ti K-edge (in toluene at 25 °C) EXAFS oscillations, FT-EXAFS spectra, and fitting curves and summary of analysis data are shown in the SI.

    43. 43
      Yi, J.; Nakatani, N.; Nomura, K.; Hada, M. Time-dependent DFT study of K-edge spectra for vanadium and titanium complexes: Effects of chloride ligands on pre-edge features. Phys. Chem. Chem. Phys. 2020, 22, 674682,  DOI: 10.1039/C9CP05891E
    44. 44
      Yi, J.; Nakatani, N.; Nomura, K. Solution XANES and EXAFS analysis of active species of titanium, vanadium complex catalysts in ethylene polymerisation/dimerisation and syndiospecific styrene polymerization. Dalton Trans. 2020, 49, 80088028,  DOI: 10.1039/D0DT01139H
    45. 45

      On the basis of EXAFS analysis, formation of the mono alkoxide CpTiCl2(OCH2C6H11) would be suggested, and further reaction did not proceed under these conditions (as expected from the reported results described in refs (46−48), shown below). NMR spectra are shown in the Supporting Information.

    46. 46
      For the reaction of CpTiCl3 with alcohols and phenol, see refs :Hafner, A.; Duthaler, R. O.; Marti, R.; Rihs, G.; Rothe-Streit, P.; Schwarzenbach, F. Enantioselective syntheses with titanium carbohydrate complexes. Part 7. Enantioselective allyltitanation of aldehydes with cyclopentadienyldialkoxyallyltitanium complexes. J. Am. Chem. Soc. 1992, 114, 23212336,  DOI: 10.1021/ja00033a005
    47. 47
      Nomura, K.; Naga, N.; Miki, M.; Yanagi, K. Olefin polymerization by (cyclopentadienyl)(aryloxy)titanium(IV) complexes-cocatalyst systems. Macromolecules 1998, 31, 75887597,  DOI: 10.1021/ma980690f
    48. 48
      Zhao, W.; Yan, Q.; Tsutsumi, K.; Nomura, K. Efficient norbornene (NBE) incorporation in ethylene/NBE copolymerization by half-titanocene catalysts containing chlorinated aryloxo ligands. Organometallics 2016, 35, 18951905,  DOI: 10.1021/acs.organomet.6b00242
    49. 49

      Reviewers commented that HCl plays a role in this catalysis. (46) However, this can be excluded due to low selectivity in the reaction with TiCl4(THF)2 under the same conditions (Table 1 and Table S1 in the Supporting Information). We have added depolymerization results (PEA 500 mg, 1.0 mol% CpTiCl3, EtOH 5.0 mL, 150 °C 6 h) after placing the premixed solution of CpTiCl3 and EtOH in vacuo (to remove volatile) in the Supporting Information (Figures S48 and S49). We confirmed completion of the depolymerization to yield diethyl adipate and EG.

  • Supporting Information

    Supporting Information

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    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acssuschemeng.2c04877.

    • General procedure, calculations for reaction products by GC and synthesis of standards, additional results in the transesterification of methyl-10-undecenoate (MU) with cyclohexanemethanol (CM) and the selected GC charts, depolymerization results, Ti K-edge XANES spectra for the catalyst solution and their EXAFS analysis data, and 13C NMR spectra for CpTiCl3 upon addition of MU and/or CM (PDF)


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