INVESTIGATIONS INTO THE KINETICS AND MECHANISM OF THE ELECTRON TRANSFER REACTIONS OF N- METHYL THIOUREA AND DIAQUOTETRAKIS(2,2’- BIPYRIDINE) - μ - OXODIRUTHENIUM (III) ION, IN AQUEOUS ACIDIC MEDIUM

The kinetics of the oxidation of n- Methyl thiourea (MTU) by diaquotetrakis (2,2’- bipyridine) - μ - oxodiruthenium (III) ion, [(bipy)4(H2O)2Ru2O]4+, in an HClO4 medium has been studied spectrophotometrically at a temperature, T = 30 ± 1°C, ionic strength, I = 0.5 mol dm-3 (NaClO4) and hydrogen ion concentration, [H+] = 5.0 x 10–2 mol dm-3. The stoichiometry of the reaction conformed to an overall equation [H2O(bipy)2RuORu(bipy)2H2O]4+ H+3CHN C NH2 + H2O 2[(H2O)2(bipy)2Ru]2+ + H3CHN C S S C NH2 NH S

• 2 NH The reaction showed first order kinetics with respect to the dimer and [MTU], respectively, k2 = (3.14 ± 0.05) x 10–2 dm3 mol–1 s–1, and was inversely affected by changes in [H+]. Changes in ionic strength and dielectric constant of reaction medium and addition of ions to the reaction medium had no or little effect on the rate constants of the reaction. The reaction has been found to conform to the rate equation: –d[[(H2O)2Ru2O4+]/ dt = (a+b 1 [𝐻+] )[[(H2O)2Ru2O4+][MTU] The reaction is considered to proceed through the formation of ion – pairs which go on to decompose at the rate determining steps to give rise to free radicals which diamerise to form the reaction products. The reduction product was found to be disulfides and the reaction is considered to proceed through the outer sphere pathway. A plausible mechanism is proposed.