Metal-ion oxidations in solution. Part X. A reinvestigation of the reactions of thiourea and its N-substituted derivatives with cobalt(III) ions in aqueous perchlorate media

Abstract

The oxidation of thiourea and its N-substituted derivatives by cobalt(III) ions has been reinvestigated, over the temperature range 8–25 °C at hydrogen-ion concentrations 0·17–1·44M, using a stopped-flow apparatus. There is no evidence for intermediate-complex formation and the observed rate constants, k_obs, may be expressed in the form k_obs=k₁+(k₂K_h/[H⁺]) where k₁ and k₂ refer to reactions involving Co³⁺(aq) and [Co(OH)]²⁺(aq) ions respectively. Thermodynamic parameters are compared with those for other oxidations of this type; the rate-determining steps are metal-ion substitution controlled with possible-effects of the sulphur-containing ligand on the cobalt(III)-ion exchange rate.