Kinetics and mechanism of Ru(III)-catalysed oxidation of amino acids by N-chloro-N-sodio-toluene-p-sulphonamide in acid media

Abstract

The kinetics of Ru(III)-catalysed oxidations of several amino acids (AA) (glycine, alanine, valine, leucine and phenyl alanine) by N-chloro-N-sodio-toluene-p-sulphonamide have been studied in aqueous perchloric acid medium under various conditions. Catalysed oxidations of all the amino acids show second-order kinetics in [oxidant], fractional order each in [AA] and Ru(III), and inverse fractional order in [H+] as compared to the second order dependence in [oxidant], first order in [AA] and inverse first order in [H+], generally observed for the uncatalysed oxidations. Variation in ionic strength of the medium or the addition of reduced product of the oxidant had no significant effect on the rates of reactions. Decrease in dielectric constant of the medium by changing the solvent composition with methanol decreased the rate in all the cases. A two-pathway mechanism has been considered to explain the observed kinetics and other effects. The rate-controlling steps have been identified in all cases and coefficients of these steps are calculated at different temperatures by varying [AA] at each temperature. Hence the activation parameters associated with the rate-controlling steps have been computed. The rate constants were also predicted from the rate laws as [AA] and [Ru(III)] were varied.