Kinetics and mechanism of hexachloroiridate(IV) oxidation of tellurium(IV) in aqueous solutions

The kinetics of oxidation of tellurium(IV) by [IrCl6](2-) in aqueous perchlorate solutions at a constant ionic strength of 0.1 mol dm(-3) have been investigated spectrophotometrically. The results showed a first-order dependence in [IrCl6](2) , fractional-first-order kinetics with respect to tellurium(IV) concentration and second-order overall kinetics. The increase in the [H+] was found to be accompanied by a decrease in the rate constants, i.e., the oxidation reaction was acid-inhibited. Kinetic evidence for the formation of a 1 : 1 intermediate binuclear complex between the two reactants has been obtained. The ionization constant of tellurium(IV) has been evaluated and found to be 1.69 x 10(-3) dm(3) mol(-1) at 25 degrees C. The kinetic parameters have been calculated and a tentative reaction mechanism consistent with the kinetic data is suggested.