Ruthenium(III) Mediated Cerium(IV) Oxidation of Thallium(I) in Aqueous Sulphuric Acid--A Kinetic and Mechanistic Study

The cerium(IV) oxidation of thallium(I) has been studied in an aqueous sulphuric acid medium. A minute amount (10 m 6 mol dm m 3 ) of ruthenium(III) is sufficient to catalyse the reaction. The reaction is first order in [cerium(IV)] in the presence of ruthenium(III) catalyst. The order in [thallium(I)] varies from zero to unity, whereas that in [ruthenium(III)] is unity. Increase in sulphuric acid concentration accelerates the reaction rate. The added products cerium(III) and thallium(III) do not significantly effect the reaction rate. The active catalyst, substrate and oxidant species are [Ru(H 2 O) 6 ] 3+ , Tl(SO 4 ) m and H 3 Ce( SO 4 ) 4 m , respectively. Possible mechanisms are proposed and the reaction constants involved have been determined.