Kinetics and Mechanism of Oxidation of Antimony (III) by Keggin-Type 12-Tungstocobaltate(III) in Aqueous Hydrochloric Acid Medium

摘要

The reaction between Sb (III) and [Co~(III)W_(12)O_(40)]~(5-) proceeds with, one-electron steps; formation of unstable Sb(IV) is the slow first step followed by tis reaction with another oxidant in a fast step. The reaction rate is unaffected by the [H~+] as there are no protonation equilibria involved with both the reactants, whereas the acceloerating effect of chloride ion is due to the formation of an active chlorocomplex of the reductant, SbCl_6~(3-). Increase in the ionic strength and decrease in 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 reactants. The activation parameters were also determined and these values support the proposed mechanism.