Thermochemical Property, Pathway and Kinetic Analysis on the Reactions of Allylic Isobutenyl Radical with O2: an Elementary Reaction Mechanism for Isobutene Oxidation

Abstract

Kinetics for the reactions of allylic isobutenyl radical (CC(C)C) with molecular oxygen are analyzed by using quantum Rice−Ramsperger−Kassel (QRRK) theory for k(E) and master equation analysis for falloff. Thermochemical properties and reaction path parameters are determined by ab initio−Moller−Plesset (MP2(full)/6-31g(d) and MP4(full)/6-31g(d,p)//MP2(full)/6-31g(d)), complete basis set model chemistry (CBS-4 and CBS-q with MP2(full)/6-31g(d) and B3LYP/6-31g(d) optimized geometries), and density functional (B3LYP/6-31g(d) and B3LYP/6-311+g(3df,2p)//B3LYP/6-31g(d)) calculations. An elementary reaction mechanism is constructed to model the experimental system, isobutene oxidation. The forward and reverse rate constants for initiation reaction C2CC + O2 ↔ CC(C)C + HO2 are determined to be 1.86 × 109 T1.301 exp(−40939 cal/RT) (cm3 mol-1 s-1) and 6.39 × 108 T0.944 exp(−123.14 cal/RT) (cm3 mol-1 s-1), respectively. Calculations on 2,5-dimethylhexa-1,5-diene, methacrolein, isobutene oxides, and acetone product f...