Oxidation of Tryptophan by Permanganate Ion in Acid, Neutral and Alkaline Media: A Comparative Kinetic and Mechanistic Study

Oxidation of tryptophan (Trp) by potassium permanganate in acid, neutral and alkaline media led to the formation of the corresponding aldehyde (indole-3-acetaldehyde), ammonia and carbon dioxide. The oxidation kinetics was studied by a spectrophotometric technique at fixed ionic strengths and ammonia and carbon dioxide. The oxidation kinetics was studied by a spectrophotometric technique at fixed ionic strengths and at 25 ᵒC. All the reactions showed a first order dependence on [MnO₄⁻] and fractional-first order kinetics in [Trp]. Fractional-second order kinetics in [H⁺] and fractional-first order dependence with respect to [OH⁻] were revealed in acid and alkaline media, respectively. An increase in the ionic strength in alkaline medium increased the oxidation rate of tryptophan, whereas it had a negligible effect on the oxidation rate in acid medium. Plausible oxidation mechanisms in all media were suggested and the rate-laws expressions were derived. Furthermore, the reactions constants included in the various steps of the suggested mechanisms were evaluated.