反式2-甲基-2-丁烯酸甲酯与臭氧反应机理的计算研究

Computational Study of the Reaction Mechanism and Kinetics of CH_3CHC(CH_3)COOCH_3Ozonolysis

采用G3B3方法构建反式2-甲基-2-丁烯酸甲酯与O3反应体系以及后续Criegee自由基有、无水分子参与下异构化反应的势能面剖面.结果表明,反式2-甲基-2-丁烯酸甲酯与O3反应首先生成一个稳定的五元环中间体,此中间体按断键位置不同后续裂解反应存在两条路径,分别生成产物P1(CH3CHOO+CH3OC(O)C(CH3)O)和P2(CH3CHO+CH3OC(O)C(CH3)OO).利用经典过渡态理论(TST)并结合Wigner矫正模型计算了200-1200 K温度区间内标题反应的速率常数kTST/W.计算结果显示,294 K时,该反应速率常数为7.55×10-18cm3molecule-1s-1,与Bernard等对类似反应所测实验值非常接近.生成的Criegee自由基(CH3CHOO和CH3OC(O)C(CH3)OO)可分别与水分子发生α-加成及β-氢迁移反应,其中Criegee自由基与水的α-加成反应较其与水的β-氢迁移反应具有优势.另外与无水分子参与CH3CHOO和CH3OC(O)C(CH3)OO异构化反应相比,水分子的参与使得异构化反应较为容易进行.

The reaction mechanism for the ozonolysis of trans-CH3CHC（CH3）COOCH3 as well as the isomerization reaction of CH3CHOO and CH3OC（O）C（CH3）OO） without and with a water molecule were investigated at the-G3B3 level. The profile of the potential energy surface （PES） was constructed. Adding ozone to trans-CH3CHC（CH3）COOCH3 via a cyclic transition state to produce a highly unstable primary ozonide that can decompose readily to form P1 （CH3CHOO＋CH3OC（O）C（CH3）O） and P2 （CH3CHO＋ CH3OC（O）C（CH3）OO） because the bond breaks in different positions. The total rate constants over the temperature range of 200-1200 K are obtained using the conventional transition state theory with Wigner tunneling correction. The calculated rate constant is 7.55x 10-18 cm3. molecule-1- s-1 at 294 K, in good agreement with previous experimental data for similar reactions. The isomerization reaction of CH3CHOO and CH3OC （O）C（CH3）OO） with a water molecule can occur via a-addition process and/3-hydrogen transfer mechanism. The former is more favorable than the latter. Compared with the naked isomerization reactions of CH3CHOO and CH3OC（O）C（CH3）OO）, the presence of water molecules makes isomerization reactions much easier