Kinetics and mechanism of the oxidation of thiosulfate ion by hexachloroiridate(IV)
In the oxidation of thiosulfate ion by hexachloroiridate(IV) ion the value Δ[IrCl62–]/Δ[S2O32–] has been determined to be 1.08 ± 0.06 (where Δ indicates concentrations used in the reaction). The reaction is first-order with respect to [S2O32–] whereas Kobs, the pseudo-first-order rate constant ([IrCl62–][S2O32–]), increased with increasing pH. The dependence of Kobs on [H+] indicated that both HS2O–3 and S2O2–3 are involved in the reduction which can only be explained on the basis of an asymmetrical structure for thiosulfuric acid. The reactivity of the S2O32– ion is almost 104 times greater than that of the HS2O3– ion. The ΔH‡ values for the two paths is almost identical indicating that the energy barrier for the electron transfer is the same in the two cases. The electron is probably transferred from the thiolic sulfur.