Kinetic and Mechanistic Investigations on Oxidation of L-tryptophan by Diperiodatocuprate(III) in Aqueous Alkaline Medium

Abstract

AbstractThe oxidation of L-tryptophan (L-TRP) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium at a constant ionic strength of 0.20 mol dm-3was studied spectrophotometrically at 298 K. The reaction between DPC and L-tryptophan in alkaline medium exhibits 1:4 stoichiometry (L-tryptophan: DPC). The reaction is of first order in [DPC] and has less than unit order in [L-TRP] and negative fractional order in [periodate] and [alkali]. Intervention of free radicals was observed in the reaction. The oxidation reaction in alkaline medium has been shown to proceed via a DPC- L-tryptophan complex, which decomposes slowly in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test, IR,1H NMR,13CNMR and LC-MS spectral studies. The reaction constants involved in the different steps of the mechanism were calculated. The activation parameters with respect to slow step of the mechanism were computed and discussed and thermodynamic quantities were also determined.