Kinetics and mechanism of oxidation of 2,3-dimethylindole by potassium peroxodisulphate

Abstract

The oxidation of 2,3-dimethylindole by potassium peroxodisulphate in dilute sulphuric acid media has been studied. The kinetic and spectrophotometric results indicate the formation of a detectable intermediate of unknown structure which decomposes to give 3-methylindole-2-carbaldehyde in low yield. The formation of the intermediate is first order in both 2,3-dimethylindole and peroxodisulphate whereas its decomposition is independent of oxidant concentration and acid-catalysed. The proposed mechanism is based on the assumption that the intermediate is a readily hydrolysable rearrangement product of the 2,3-dimethyl-3H-indol-3-yl sulphate formed from electrophilic attack of peroxodisulphate at C-3 involving nucleophilic displacement of peroxide oxygen.