Criegee中间体CH3CHOO与H2O反应机理及酸催化效应

采用CCSD（T）//B3LYP/6-311+G（d，p）方法研究了H₂O及甲酸等6种有机酸对CH₃CHOO与H₂O加成反应的催化作用。结果表明，非催化反应存在双质子迁移和加成反应2条通道，其中加成反应为优势通道。其加成机理为H₂O中OH加到CH₃CHOO的α-C上，同时H₂O中另一个H迁移到CH₃CHOO的端O上。催化剂H₂O及有机酸以氢键复合物的形式参与反应促进了H质子转移，可降低基元反应能垒和表观活化能，且催化效应与有机酸的强度成正比。例如，当分别用H₂O（pK_a=15.7）、甲酸（pK_a=3.75）和草酸（pK_a=1.23）催化时，生成syn-HAHP的基元反应能垒由非催化的69.12 kJ·mol^-1分别降至40.78、18.88和10.61 kJ·mol^-1。非催化反应具有正的表观活化能，而所有催化反应则均具有负的表观活化能。

Reaction Mechanism of Criegee Intermediate CH3CHOO with H2O and the Acid Catalytic Effect

The catalytic effect of H₂O and six kinds of organic acids (e.g., formic acid) on the reaction of CH₃CHOO with H₂O is studied at the CCSD(T)//B3LYP/6-311+G(d,p) level. The results reveal that two possible channels exist as the double proton transfer and addition, of which the latter dominates for the non-catalytic reactions. For the additions, the OH of water is added to the α-C of CH₃CHOO, and the H atoms migrate to the end oxygen atoms. Catalysts such as H₂O and organic acid can form a hydrogen-bonded complex with CH₃CHOO, which promotes the H transfer and thus significantly reduces the elementary reaction energy barrier and apparent activation energy when compared with that of the non-catalytic reaction. The catalytic effect is proportional to the strength of the organic acids. For example, for the formation of syn-HAHP catalyzed by H₂O (pK_a=15.7), formic acid (pK_a=3.75) and oxalic acid (pK_a=1.23), the energy barrier is reduced from 69.12 to 40.78, 18.88 and 10.61 kJ·mol^-1, respectively. In addition, the non-catalytic reaction has a positive activation energy, whereas the catalytic reactions have an negative apparent activation energy.