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Kinetics and Mechanism of Keggin Type 12-Tungstocobaltate (II) Catalyzed Potassium Iodide Oxidation by Perborate

D. S. Rajmane and G. S. Gokavi

The oxidation of potassium iodide by perborate catalyzed by Keggin type [Co(II)W12O40]6- has been studied in sulphuric acid medium. The reaction proceeds by the oxidation of [Co(II)W12O40]6- to [Co(III)W12O40]5- by hydrogen peroxide, generated by the decomposition of perborate, which then oxidizes potassium iodide in a rate determining step. The reaction was found to be independent of [H+]. 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.