Mechanistic Investigations of Ruthenium(III) Catalyzed Oxidation of L-Tryptophan by Diperiodatocuprate(III) in Aqueous Alkaline Media (Stopped Flow Technique): A Kinetic Study

The kinetics of the oxidation of ruthenium(III) (Ru(III)) catalyzed oxidation of L-tryptophan (L-trp) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium at a constant ionic strength of 0.20 mol dm -3 was studied spectrophotometrically. The reaction between L-tryptophan and DPC in alkaline medium in presence of [Ru(III)] exhibits 1:4 stoichiometry (L-trp:DPC). The reaction was of first order in [DPC], less than unit order in [L-trp] and negative fractional order in both [OH ] and [IO4 ]. The order in [Ru(III)] was unity. Intervention of free radicals was observed in the reaction. The oxidation reaction in alkaline medium has been shown to proceed via a Ru(III)-L-trp complex, which reacts with monoperiodatocuprate(III) to decompose in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test, IR, NMR and LC-MS. Probable mechanism is proposed and discussed. The activation parameters with respect to the slow step of the mechanism were computed and discussed and thermodynamic quantities were also calculated. The active species of catalyst and oxidant have been identified.