Kinetics of the autoxidation of toluene catalysed by cobaltic acetate

Abstract

The autoxidation of toluene catalysed by cobaltic acetate in acetic acid at 90° has been studied kinetically in order to clarify the reaction mechanism. When a cobaltic salt catalyst alone is used rather than cobaltous acetate together with a promoter, the autoxidation gives benzoic acid. The rate is proportional to the concentration of toluene and cobaltic acetate. The rate constant increases with increasing oxygen percentage at low concentrations of oxygen (below 42 percent in a mixture of oxygen and nitrogen), but is independent of it at high oxygen percentage (above 42 per cent). The addition of a small amount of aldehyde (below 0·0374M) shortened the induction period, while the addition of a large amount of aldehyde (above 0·0601M) gave an early increase in the rate. The addition of benzyl alcohol, however, inhibits the reaction. A probable mechanism is suggested and discussed, which involves a hydrogen abstraction from the methyl group of toluene by cobaltic ion, benzoyl-oxy-and/or peroxyradicals.