Kinetics and mechanism of oxidation of neutral ? -amino acids by sodium N-chloro-p-toluenesulfonamide in acid medium

Abstract

Kinetics of oxidation of α -amino acids, glycine, valine, alanine, and phenylalanine, by sodium N-chloro-p-toluenesulfonamide or chloramine-T (CAT) has been investigated in HClO4 medium at 30°C. The rate shows first-order dependence on both CAT and amino acid concentrations and an inverse first-order on [H+]. The variation of ionic strength and the addition of p-toluenesulfonamide and Cl− ion had no effect on the reaction rate. Decrease of dielectric constant of the medium by increasing the MeOH content decreased the rate. Rate studies in D2O medium showed the inverse solvent-isotope effect of kD2O/kH2O=0.50. Proton-inventory studies were carried out using H2O–D2O mixtures. The activation parameters have been computed. The proposed mechanism and the derived rate law are consistent with the observed kinetic data. An isokinetic relationship is observed with β=323 K, indicating enthalpy as a controlling factor. The rate of oxidation increases in the following order: Gly < Val < Phe < Ala. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 49–55, 2002