Theoretical study of the oxidation reactions of methylacrylic acid and methyl methacrylate by triplet O2.
The oxidations of organic compounds and polymers by triplet O2 were called "dark oxidation" or "auto-oxidation", in contrast to their "photo-oxidation" by singlet O2. To study the relevant dark oxidation mechanism we take methylacrylic acid (MAA) and methyl methacrylate (MMA) as prototypes to study their reactions with triplet O2 by performing density functional theory calculations. Two reaction channels, the C-H bond oxidation and C=C bond oxidation, have been characterized in detail. The structures of the initial contact charge-transfer complexes, intermediates, transition states, and final oxides involved in the reactions have been localized at the UB3LYP/6-311+G(d,p) level. It is found that the C-H bond in the methyl group connected to the C=C bond presents relatively higher reactivity toward triplet O2 than the C=C bond itself. Thus, the reactions are expected to proceed via the C-H bond oxidation branch at room temperature and also via C=C bond oxidation at elevated temperature. In this sense, an effective method for preventing or retarding the dark oxidations of MAA and MMA in a natural environment is to chemically decorate or protect the C-H bond in the methyl connected to the C=C bond. The present results are expected to provide a general guide for understanding the dark oxidation mechanism of organic compounds and polymers.
Wang
Guixiu
G
Institute of Theoretical Chemistry, Shandong University, Jinan 250100, P. R. China.
Zhang
Dongju
D
Xu
Xiaohong
X
Zhou
Jianhua
J
D008689:Methacrylates / Q000737:chemistry*; D020366:Methylmethacrylate / Q000737:chemistry*; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*
D008689:Methacrylates; D020366:Methylmethacrylate; C008384:methacrylic acid; D010100:Oxygen