Kinetics and mechanisms of the oxidation reactions of some 2,3-dialkylindole derivatives by peroxodisulfate and peroxomonosulfate anions

Abstract

The kinetics and mechanisms of the oxidation of several 2,3-dialkylindoles, 2-methyl-3-ethyl-, 1b; 2-ethyl-3-methyl-,1c; 1,2,3-trimethyl-, 1d; 2-phenyl-3-methyl-, 1e and 1,2,3,4-tetrahydrocarbazole 2 by peroxomonosulfate and peroxodisulfate anions have been investigated in sulfuric acid 0.1 mol dm^–3 and 20% v/v methanol-water solutions. For each, the reaction pathway starts with the electrophilic attack of the peroxidic bond at the C-3 atom of the indole ring to give an indoleninic intermediate. The subsequent steps depend on the viability of the tautomerization of this indoleninic intermediate to an exocyclic enamine. Thus, in those cases where the short-lived enamine derivative is favoured, a second peroxoanion molecule attacks the exocyclic 2-methylene group to give a new intermediate, which, after hydrolysis, produces a 2-acylindole derivative. However, in those cases where the imine is favoured, there is not a second peroxoanion attack, the reaction products being the imine or an oxoindolic derivative.