Redox Kinetics and Mechanism of the Oxidation of Thiourea by Diaquotetrakis(2,2’- Bipyridine) - µ - Oxodiruthenium (III) Ion, in Aqueous Perchloric Acid

The kinetics of the oxidation of thiocarbamide (thiourea) by diaquotetrakis(2,2’- bipyridine) - µ - oxodiruthenium (III) ion, [(bpy)2(H2O)RuORu(H2O)(bpy)2]4+, in perchloric acid has been investigated at a temperature, T = 30±1ºC, ionic strength, I = 0.5 mol dm-3 (NaClO4) and hydrogen ion concentration, [H+] = 5.0 x 10–2 mol dm-3. The reaction showed a stoichiometry of 1:2 (oxidant/ thiourea), first order kinetics with respect to the thiourea (RSH), k2 = (7.39±0.05) dm3 mol–1 s–1, inverse [H+] dependence and zero salt effect. The rate equation for the reaction has been proposed –d[(bpy)2(H2O)RuORu(H2O)(bpy)2]4+]/dt=(a+b )[(bpy)2(H2O)RuORu(H2O)(bpy)2]4+[RSH]. Outer sphere mechanism is implicated to operate in this reaction as evidenced by lack of the formation of a stable intermediate complex as suggested by absence of intercept in the Michaelis - Menten plot, lack of shift in λmax of the reaction mixture 1 minute after start of reaction and absence of observable anion catalysis. A plausible mechanism is proposed.