Chemically activated formation of organic acids in reactions of the Criegee intermediate with aldehydes and ketones
Chemically activated formation of organic acids in reactions of the Criegee intermediate with aldehydes and ketones
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DOI：
10.1039/c3cp52598h
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发表时间：
2013-01-01
影响因子：
3.3
通讯作者：
Green, William H.
中科院分区：
文献类型：
--
作者：
Jalan, Amrit;Allen, Joshua W.;Green, William H.
Criegee中间体（Cl，（CH_2OO中心点）-C中心点）反应在大气臭氧分解模型中具有重要意义。在这项工作中，我们计算（CH_2 OO中心点）-C-中心点与甲醛，CH_3CHO和CH_3COCH_3之间的反应速率，导致形成二级臭氧化物（SOZ）和有机酸。相对于无限分离的反应物，发现在所有三种情况下的SOZ的能量低48-51 kcal mol（-1），通过（CH 2 OO中心点）-C-中心点跨C=O键的1，3-环加成形成。发现SOZ分解的最低能量途径是由O-O键裂解形成羟烷基酯的单线态双自由基中间体的分子内缩合。这些羟烷基酯经历协同分解，提供从SOZ到酸的低能量途径。使用B3 LYP/MG 3S DFT模型化学获得所有固定点的几何构型和频率，并且使用RCCSD（T）-F12 a/cc-pVTZ-F12单点计算来细化能量。RRKM计算用于获得微正则速率系数（k（E）），并且使用储层状态方法获得温度和压力依赖的速率系数（k（T，P））和产物支化比。在常压下，碰撞稳定SOZ的产率按HCHO <CH_3CHO <CH_3COCH_3的顺序增加（最高产率比初始（CH_2 OO中心点）-C-中心点浓度低10 ~（-4）倍）。在低压下，化学活化形成的有机酸（甲酸的情况下，甲醛和CH 3COCH 3，甲酸和乙酸的情况下，CH 3CHO）被认为是与最近的直接测量协议的主要产品通道。碰撞能量传递参数和SOZ反应的势垒高度是决定SOZ和有机酸产率的最敏感参数。
Reactions of the Criegee intermediate (CI, (CH2OO center dot)-C-center dot) are important in atmospheric ozonolysis models. In this work, we compute the rates for reactions between (CH2OO center dot)-C-center dot and HCHO, CH3CHO and CH3COCH3 leading to the formation of secondary ozonides (SOZ) and organic acids. Relative to infinitely separated reactants, the SOZ in all three cases is found to be 48-51 kcal mol(-1) lower in energy, formed via 1,3-cycloaddition of (CH2OO center dot)-C-center dot across the C=O bond. The lowest energy pathway found for SOZ decomposition is intramolecular disproportionation of the singlet biradical intermediate formed from cleavage of the O-O bond to form hydroxyalkyl esters. These hydroxyalkyl esters undergo concerted decomposition providing a low energy pathway from SOZ to acids. Geometries and frequencies of all stationary points were obtained using the B3LYP/MG3S DFT model chemistry, and energies were refined using RCCSD(T)-F12a/cc-pVTZ-F12 single-point calculations. RRKM calculations were used to obtain microcanonical rate coefficients (k(E)) and the reservoir state method was used to obtain temperature and pressure dependent rate coefficients (k(T, P)) and product branching ratios. At atmospheric pressure, the yield of collisionally stabilized SOZ was found to increase in the order HCHO < CH3CHO < CH3COCH3 (the highest yield being 10(-4) times lower than the initial (CH2OO center dot)-C-center dot concentration). At low pressures, chemically activated formation of organic acids (formic acid in the case of HCHO and CH3COCH3, formic and acetic acid in the case of CH3CHO) was found to be the major product channel in agreement with recent direct measurements. Collisional energy transfer parameters and the barrier heights for SOZ reactions were found to be the most sensitive parameters determining SOZ and organic acid yield.