Tadayon Sara V, Foreman Elizabeth S, Murray Craig
Department of Chemistry, University of California, Irvine , Irvine California 92697, United States.
J Phys Chem A. 2018 Jan 11;122(1):258-268. doi: 10.1021/acs.jpca.7b09773. Epub 2017 Dec 29.
Reactions of the simplest Criegee intermediate (CHOO) with a series of alcohols have been studied in a flash photolysis flow reactor. Laser photolysis of diiodomethane at 355 nm in the presence of molecular oxygen was used to produce CHOO, and the absolute number densities were determined as a function of delay time from analysis of broadband transient absorption spectra obtained using a pulsed LED. The kinetics for the reactions of CHOO with methanol, ethanol, and 2-propanol were measured under pseudo-first-order conditions at 295 K, yielding rate constants of (1.4 ± 0.4) × 10 cm s, (2.3 ± 0.6) × 10 cm s, and (1.9 ± 0.5) × 10 cm s, respectively. Complementary ab initio calculations were performed at the CCSD(T)/aug-cc-pVTZ//CCSD/cc-pVDZ level of theory to characterize stationary points on the reaction enthalpy and free energy surfaces and to elucidate the thermochemistry and mechanisms. The reactions proceed over free energy barriers of ∼8 kcal mol to form geminal alkoxymethyl hydroperoxides: methoxymethyl hydroperoxide (MMHP), ethoxymethyl hydroperoxide (EMHP), and isopropoxymethyl hydroperoxide (PMHP). The experimental and theoretical results are compared to reactions of CHOO with other hydroxylic compounds, such as water and carboxylic acids, and trends in reactivity are discussed.
在闪光光解流动反应器中研究了最简单的克里吉中间体（CHOO）与一系列醇类的反应。在分子氧存在下，通过355 nm激光光解二碘甲烷来生成CHOO，并根据使用脉冲发光二极管获得的宽带瞬态吸收光谱分析，确定绝对数密度作为延迟时间的函数。在295 K的准一级条件下测量了CHOO与甲醇、乙醇和2-丙醇反应的动力学，得到的速率常数分别为(1.4±0.4)×10 cm s、(2.3±0.6)×10 cm s和(1.9±0.5)×10 cm s。在CCSD(T)/aug-cc-pVTZ//CCSD/cc-pVDZ理论水平上进行了补充性的从头算计算，以表征反应焓和自由能表面上的驻点，并阐明热化学和反应机理。反应通过约8 kcal mol的自由能垒进行，生成偕二烷氧基甲基氢过氧化物：甲氧基甲基氢过氧化物（MMHP）、乙氧基甲基氢过氧化物（EMHP）和异丙氧基甲基氢过氧化物（PMHP）。将实验和理论结果与CHOO与其他羟基化合物（如水和羧酸）的反应进行了比较，并讨论了反应活性趋势。
