Effect of strong acids on the oxidation of alkylarenes by manganic and cobaltic acetates in acetic acid

Abstract

The oxidation of alkylarenes by both manganic and cobaltic acetates in acetic acid is so enhanced by strong acids that extensive transformations can be achieved at room temperature. Under these conditions, only products from side-chain oxidation are obtained and the formation of nuclear adducts reported in previous studies with manganic acetate has not been observed. The products obtained are different according to whether oxygen is present or not. Under nitrogen, benzylic acetates predominate whereas carbonyl compounds are favoured when oxygen is present. The activating effect of strong acids on the oxidizing properties of manganic and cobaltic acetates seems to be primarily related to their ability to release protons. In the case of cobaltic acetate, this effect appears to be partly the result of a modification in the association state of cobalt atoms. In concentrated systems, Co^III and Co^II are apparently associated in dimeric structures and the effect of strong acids may be to dissociate such dimers with liberation of reactive cobaltic species. The mechanism of attack of alkylarenes is discussed.