Kinetic, spectroscopic and potentiometric studies of the redox reactions of the iron (III) and copper (II) thiosulfate complexes

The mechanism of the copper(II)-catalysed oxidation of thiosulfate ion by iron(III) in aqueous solutions is poorly understood, but is of interest because of its analytical applications, and its relevance to the disposal of waste solutions of thiosulfate and sulfoxyanions in general. The aim of this study was to determine or confirm the mechanisms of the reactions between copper(H) and thiosulfate, iron(III) and thiosulfate, and the reaction of aqueous mixtures of both metal ions with thiosulfate. This was done with a view to assessing the application of these reactions in both existing and proposed analytical procedures for the determination of copper and/or iron in aqueous media, with techniques such as flow-injection analysis. Stopped-flow and continuous flow methods were employed both to characterise the short-lived, coloured complexes of copper(II) and iron(III) with thiosulfate and to record kinetic data for the study of their rapid decomposition reactions. In addition, Raman spectra of frozen solutions of the iron (III)-thiosulfate complex were recorded for the first time.