Kinetics and mechanism of the oxidation of iodide by diaquote- trakis(2,2′-bipyridine)-μ-oxodiruthenium(III) ion in acid medium

Summary

The kinetics of the oxidation of iodide by diaquotetrakis-(2,2-bipyridine)-μ-oxodiruthenium(III), [Ru₂O]⁴⁺, were studied in aqueous perchloric acid at 25.0±0.1°C, I = 1.0 M (NaClO₄). The reaction conforms to the overall equation: $$ {⤪ [Ru_{2}O]^{4+}+I^{-}⌝ghtarrow [Ru_{2}O]^{3+}+{1⩈er 2}I_{2}} $$ The experimental data are consistent with a second-order rate law: $$ {⤪ -d[Ru_{2}O^{4+}]/dt=k_{2}[Ru_{2}O^{4+}][I^{-}]} $$ with k₂ = (3.5 ± 0.2) × 10⁻² M⁻¹ s⁻¹ at [H⁺] = 0.05 M. Added Li⁺, K⁺, Na⁺, Mg²⁺, Zn²⁺, Cl⁻, Br⁻ and $ {⤪ NO_{3}^{-}} $ had no effect on the rate of the reaction. The reaction rate was independent of variation in the ionic strength of the reaction medium in the range 0.25 ⩽ I ⩽ 2.0 M, but linearly dependent on [H⁺] in the acid range 0.05 ⩽ [H⁺] ⩽ 1.0 M. The absence of both kinetic and spectroscopic evidence for complex formation suggests that the reaction proceeds by the outer-sphere mechanism; this deduction is further supported by the non-conformity of the rate data to the Michaelis-Menten equation.