Mechanism of Ru(III)-catalyzed oxidation of L-cystine by Ce(IV) ions in sulphuric acid medium

Abstract

Mechanism of oxidation of L-cystine by acidic solution of Ce(IV) ions in the presence of Ru(III) ions as homogeneous catalyst was studied using kinetic approach. A first-order dependence of the reaction rate on [cystine] and [Ce(IV)] was observed. The rate is inversely proportional to [H+] and decreased with increasing ionic strength of the medium. The active species of the oxidant in sulphuric acid medium and that of the catalyst were Ce(SO4)2 and [RuCl2(H2O)4]+ respectively. A suitable mechanism based on the kinetic data is proposed. The activation parameters and the thermodynamic quantities were also evaluated which supported the proposed mechanisms.