Solvent effects on the kinetics of oxidation of cysteinatobis(ethylenediamine)cobalt(III) ion by peroxodisulphate

Abstract

The kinetics of oxidation of cysteinatobis(ethylenediamine)cobalt(III) ion, [Co(CysOS)(en)₂]⁺, by peroxodisulphate were investigated at different ionic strengths, adjusted with various electrolytes, and at different temperatures and concentrations of perchloric acid. Rate constants and activation parameters are also reported for this oxidation in mixtures containing up to 40% acetone, t-butyl alcohol, isopropyl alcohol, or acetonitrile. The solubilities of [Co(CysOS)(en)₂]ClO₄ and KClO₄ have been determined in water and aqueous acetone and aqueous t-butyl alcohol at 298.2 K. From these values, Gibbs free energies of transfer for [Co(CysOS)(en)₂]⁺ and S₂O₈^2– have been estimated. The solvent effects on the oxidation have been divided into their initial-state and transition-state components.