Kinetics and Mechanism of the Reduction of Tetraoxochromate(VI) by Thiophenol

P. O. Ukoha, S. O. Okonkwo, N. N. Ukwueze, O. T. Ujam


The kinetics and mechanism of the reduction of tetraoxochromate(VI), to chromium(III) by thiophenol, was studied in aqueous perch loric acid at 27±0.5°C, I = 0.05 mol dm-3 (NaClO4), [H+] = 0.5 mol dm-3 and λmax = 350 nm.  Spectrophotometric titration following the Yoe-Jones method gave a point of inflexion at the mole ratio of 1:1 inferring that one mole of the oxidant was consumed as one mole of the reductant was oxidized.  Kinetic decays indicated first order dependence of the reaction on both oxidant and reductant and gave the reaction as second order overall. Pseudo-first order rate constants increased with increase in concentration of the reductant and k2 values were constant within 0.114±0.006 dm3mol-s-1.  The reaction rate increased with [H+] and ionic strength. Catalytic effects by CH3COO- and Cl- was not very significant. The reaction was rationalized on the basis of two parallel routes: an outer-sphere path that is non-acid dependent and an inner-sphere route that is acid dependent. 

Keywords: kinetics, mechanisim, tetraoxochromate(VI), reduction, thiophenol, chromium(III) 

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