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

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• 作者：Thomas G. Custer ; Shuji Kato ; Veronica M. Bierbaum ; Carleton J. Howard ; and Glenn C. Morrison
• 刊名：Journal of the American Chemical Society
• 出版年：2004
• 出版时间：March 10, 2004
• 年：2004
• 卷：126
• 期：9
• 页码：2744 - 2754
• 全文大小：215K
• 年卷期：v.126,no.9(March 10, 2004)
• ISSN：1520-5126

文摘

The gas-phase reactions of protonated hydrazine (hydrazinium) with organic compounds werestudied in a selected ion flow tube-chemical ionization mass spectrometer (SIFT-CIMS) at 0.5 Torr pressureand ~300 K and with hybrid density functional calculations. Carbonyl and other polar organic compoundsreact to form adducts, e.g., N₂H₅⁺(CH₃CH₂CHO). In the presence of neutral hydrazine, aldehyde adductsreact further to form protonated hydrazones, e.g., CH₃CH₂CH=HNNH₂⁺ from propanal. Using deuteratedhydrazine (N₂D₄) and butanal, we demonstrate that the gas-phase ion chemistry of hydrazinium andcarbonyls operates by the same mechanisms postulated for the reactions in solution. Calculations provideinsight into specific steps and transition states in the reaction mechanism and aid in understanding thelikely reaction process upon chemical or translational activation. For most carbonyls, rate coefficients foradduct formation approach the predicted maximum collisional rate coefficients, k ~ 10^-9 cm³ molecule^-1s^-1. Formaldehyde is an exception (k ~ 2 × 10^-11 cm³ molecule^-1 s^-1) due to the shorter lifetime of itscollision complex. Following adduct formation, the process of hydrazone formation may be rate limiting atthermal energies. The combination of fast reaction rates and unique chemistry shows that protonatedhydrazine can serve as a useful chemical-ionization reagent for quantifying atmospheric carbonyl compoundsvia CIMS. Mechanistic studies provide information that will aid in optimizing reaction conditions for thisapplication.