Oxidation mechanism of aliphatic ethers : theoretical insights on the main reaction channels
Résumé
This paper presents a quantum chemical study on oxidation process of a series of aliphatic ethers. On the basis of a detailed theoretical work on diethyl ether oxidation, the mechanism has been reduced at three competing reactions: the beta-scission of the alkyl radical (R(I)OR(II)(.)) issued from the initiation step, the isomerization of the peroxy radical (R(I)OR(II)OO(.)) produced by reaction of the alkyl radical with molecular oxygen, and the hydroperoxide production, a bimolecular reaction between the peroxy radical and an ether molecule that also regenerates a R(I)OR(II)(.) radical. Results obtained from DFT calculations, including thermochemistry and rate constant evaluations, have been reported and discussed. The influence of the presence of the oxygen atom in the ether skeleton has been evaluated by making a comparison between some ethers and parent hydrocarbons. In particular, it has been found that oxygen increases the reactivity of vicinal sites by lowering activation barriers and favors the stabilization of radicals. Direct proportionality relationships have been searched between activation and reaction enthalpies of each class of competing reactions, but one has been found only for the isomerization reaction.