Abstract
A mechanistic model is presented for the CuII-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 S2O32– 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.