Kinetic and mechanistic studies of oxidation of glycine and valine by N-bromosuccinimide using chloro complex of Rh(III) in its nano-concentration range as homogeneous catalyst

Abstract

Kinetics of oxidation of glycine (gly) and valine (val) by N-bromosuccinimide (NBS) using chloro complex of Rh(III) in its nano-concentration range as homogeneous catalyst have been investigated at 35 ^oC . The reaction shows first order kinetics with respect to NBS and Rh(III) in the oxidation of both the amino acids. The first order kinetics with respect to amino acid obtained at its lower concentration changes to zero order at its higher concentration. Inverse fractional order with respect to [H⁺] was obtained in Rh(III)-catalysed oxidation of gly and val. Variation in [Hg(II)], [NHS], [Cl^-], ionic strength and dielectric constant of the medium has no effect on the rate of oxidation of both the amino acids. NBS itself and [RhCl₅(H₂O)]^2-have been postulated as the reactive species of NBS and Rh(III) chloride in acidic medium, respectively. Various activation parameters have been calculated with the pseudo-first-order rate constant values observed at four different temperatures. The main oxidation products of the reactions have been identified as formaldehyde and ammonia in the case of gly and isobutaldehyde and ammonia in the case of val. The proposed reaction mechanism is well supported by kinetic data, spectrophotometric evidence and positive entropy of activation.