Mechanism of oxidation of selenium(IV) by cobalt(III) in perchloric acid — a kinetic study

Summary

The kinetics of Co^III oxidation of Se^IV have been studied in aqueous HClO₄. The order with respect to Co^m is two the order with respect to Se^IV is one at low concentrations; two at high concentrations. The latter variation is attributed to the greater reactivity of the Se^IV dimier A mechanism involving complexation between oxidant and substrate is proposed. [CoOH]²⁺ is presumed to be the reactive Co^III species and H₂SeO₃ and HSeO ⁻₃ to be those of Se^IV. At 25° C, E_a, ΔH^‡ and ΔS^‡ for the monomeric path are 125.6±4.0 kJ mol⁻¹, 122.1±3.8 kJ mol⁻¹ and 206±12 JK⁻¹ mol⁻¹ respectively and those for the dimeric path are 88.6±3.6 kJ mol⁻¹, 85.9±3.4 kJ mol⁻¹ and 62.6±11.3 JK⁻¹ mol⁻¹ respectively.