OXIDATION OF 2,3-DIMETHYLINDOLE BY PEROXOPHOSPHATES

The kinetics of the oxidation of 2,3-dimethylindole 1 by peroxodiphosp horic, PDP, and peroxomonophosphoric, PMP, acids have been investigate d in sulfuric acid (0.1-1 mol dm(-3)) and 20% v/v methanol-water solut ions, On the basis of the spectral and kinetic results and by analogy with the mechanism previously proposed for the oxidation of 1 by perox omono- and peroxodi-sulfate anions, we have concluded that the reactio ns proceed through the following steps: an electrophilic attack of the peroxide bond at the C-3 atom of the indole ring to form an indolenin ic intermediate, a second peroxo attack on the enaminic tautomer of th is intermediate and the hydrolysis of the product to finally give 3-me thylindole-2-carbaldehyde. The analysis of the dependence of the react ion rates with acidity shows that, under our experimental conditions, neutral H4P2O8 and cationic H4PO5+ are, respectively, the active speci es mainly involved in the oxidation processes.