A kinetic study of the reaction between thiourea and ethylenediaminetetraacetato ruthenate(III) complex by the stopped flow technique

Abstract

The kinetics of reaction between thiourea and [Ru^III (H-EDTA)(H₂O)] (1) were investigated in aqueous solution as a function of pH, temperature and metal ion concentration at 0.1 M ionic strength using the stopped flow technique. It was established that the monoanionic species of complex 1, [Ru^IIIEDTA)(H₂O)]⁻ (2) is the major reacting species over the pH range 1.5-8.5. The substitution reaction follows first-order kinetics in [Ru(EDTA)(H₂O)]⁻ as well as in thiourea concentrations over a wide concentration range of the two reactants. The rate constant (k₁) was found to be (2.04±0.17) ×10³M⁻¹ s⁻¹ at 25°C and μ=0.1 M (KCl). From the activation parameters of the reaction it was concluded that the substitution reaction of [Ru(EDTA)H₂O]⁻ follows an associative mechanism. The reactivities of different species of the thiourea complexes formed, have also been discussed.