Abstract

The oxidation of hexacyanoferrate(II) by perborate catalyzed by Keggin type [Co^IIW₁₂O₄₀]^6- has been studied in sulphuric acid medium. The reaction proceeds by the oxidation of [Co^IIW₁₂O₄₀]^6- to [Co^IIIW₁₂O₄₀]^5- by hydrogen peroxide, generated by the decomposition of perborate, which then oxidizes hexacyanoferrate(II) to hexacyanoferrate(III) in a rate determining step. The reaction was found to be inhibited by increase in the [H⁺] due to conversion of active hexacyanoferrate(II) into an inactive protonated form. Decreasing the relative permittivity of the medium increases the rate of the reaction which is attributed to the formation of an outer-sphere complex between the catalyst and active oxidant. The activation parameters were also determined and the values support the proposed mechanism.

Keywords

Kinetics, Mechanism, Hexacyanoferrate(II) oxidation, Perborate