Model for the oscillatory reaction between hydrogen peroxide and thiosulfate catalysed by copper(II) ions

Abstract

A mechanistic model is presented for the Cu^II-catalysed oxidation of thiosulfate by hydrogen peroxide, which gives oscillatory behaviour in a flow reactor. A simple four-step model, in which formation of the intermediate HOS₂O₃^– and attack on that species by H₂O₂ and S₂O₃^2– play key roles, suffices to give oscillatory behaviour. By extending this core set of reactions with additional steps that describe acid–base equilibria and reactions between H₂O₂ and sulfur species, we obtain better agreement with the observed oscillatory behaviour as well as the ability to simulate the observed batch behaviour and the bistability and complex multi-peaked oscillations found in flow systems. Our results suggest that mechanistic descriptions of sulfur-containing hydrogen peroxide oscillators should emphasize the capability of the sulfur substrate to be partially oxidized to a relatively stable intermediate prior to its total oxidation to sulfate.