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Gas-Phase Kinetics and Mechanism of the Reactions of Protonated Hydrazine with Carbonyl Compounds. Gas-Phase Hydrazone Formation: Kinetics and Mechanism

Supporting Info

Thomas G. Custer,^† Shuji Kato,^† Veronica M. Bierbaum,^† Carleton J. Howard,^‡^§ and Glenn C. Morrison*^‡

Contribution from the Department of Chemistry and Biochemistry, University of Colorado, 215 UCB, Boulder, Colorado 80309-0215, National Oceanic and Atmospheric Administration (NOAA), Aeronomy Laboratory R/AL2 325 Broadway, Boulder, Colorado 80305, Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Campus Box 216, Boulder, Colorado 80309

J. Am. Chem. Soc., 2004, 126 (9), pp 2744–2754

DOI: 10.1021/ja0350886

Publication Date (Web): February 14, 2004

†

Department of Chemistry and Biochemistry, University of Colorado.

‡

National Oceanic and Atmospheric Administration.

Retired, current e-mail address: cjhome@comcast.net.

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

Cooperative Institute for Research in Environmental Sciences, University of Colorado.

Current address: Department of Civil Engineering, 221 Butler-Carleton Hall, University of Missouri−Rolla, Rolla, MO 65409-0030.

, gcm@umr.edu

Abstract

The gas-phase reactions of protonated hydrazine (hydrazinium) with organic compounds were studied in a selected ion flow tube−chemical ionization mass spectrometer (SIFT-CIMS) at 0.5 Torr pressure and 300 K and with hybrid density functional calculations. Carbonyl and other polar organic compounds react to form adducts, e.g., N₂H₅⁺(CH₃CH₂CHO). In the presence of neutral hydrazine, aldehyde adducts react further to form protonated hydrazones, e.g., CH₃CH₂CHHNNH₂⁺ from propanal. Using deuterated hydrazine (N₂D₄) and butanal, we demonstrate that the gas-phase ion chemistry of hydrazinium and carbonyls operates by the same mechanisms postulated for the reactions in solution. Calculations provide insight into specific steps and transition states in the reaction mechanism and aid in understanding the likely reaction process upon chemical or translational activation. For most carbonyls, rate coefficients for adduct formation approach the predicted maximum collisional rate coefficients, k 10^-⁹ cm³ molecule^-¹ s^-¹. Formaldehyde is an exception (k 2 × 10^-¹¹ cm³ molecule^-¹ s^-¹) due to the shorter lifetime of its collision complex. Following adduct formation, the process of hydrazone formation may be rate limiting at thermal energies. The combination of fast reaction rates and unique chemistry shows that protonated hydrazine can serve as a useful chemical-ionization reagent for quantifying atmospheric carbonyl compounds via CIMS. Mechanistic studies provide information that will aid in optimizing reaction conditions for this application.