KINETICS AND MECHANISMS OF THE OXIDATION REACTIONS OF SOME 2,3-DIALKYLINDOLE DERIVATIVES BY PEROXODISULFATE AND PEROXOMONOSULFATE ANIONS

The kinetics and mechanisms of the oxidation of several 2,3-dialkylind oles, 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 peroxo monosulfate and peroxodisulfate anions have been investigated in sulfu ric acid (0.1 mol dm(-3) and 20% v/v methanol-water solutions. For eac h, the reaction pathway starts with the electrophilic attack of the pe roxidic bond at the C-3 atom of the indole ring to give an indoleninic intermediate. The subsequent steps depend on the viability of the tau tomerization of this indoleninic intermediate to an exocyclic enamine. Thus, in those cases where the short-lived enamine derivative is favo ured, 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 fa voured, there is not a second peroxoanion attack, the reaction product s being the imine or an oxoindolic derivative.