Color Reactions of Aqua(ethylenediaminetetraacetato)ruthenate(III) with Sulfur Compounds. Kinetic Study of Thiosulfate Anation

Abstract

Abstract New color reactions of aqua(ethylenediaminetetraacetato)ruthenate(III) with sulfur compounds such as thiols, thiourea and thiosulfate have been found and investigated. It has been established that the coloration is due to the anation of the complex with sulfur compounds. In the case of thiosulfate, the reaction is first order in either reactant and independent of [H+] in the pH range 4 to 6. The rate constant (kAN) was found to be 2.94±0.11 M−1 s−1 at 30 °C and I=0.1. For a pH>6, the rate decreases with increase in pH due to the formation of a hydroxo complex. In the higher pH region, the reverse reaction, [Ru(edta) (S2O3)]3−+OH−\ightleftarrows[Ru(edta) (OH)]2−+S2O32− takes place. From the value of the equilibrium constant (Keq) for this reaction, the equilibrium constant (KAN) for thiosulfate anation has been estimated as, logKAN=5.02 at 30 °C and I=0.1.