MODEL FOR THE OSCILLATORY REACTION BETWEEN HYDROGEN-PEROXIDE AND THIOSULFATE CATALYZED BY COPPER(II) IONS

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 i ntermediate HOS2O3- and attack on that species by H2O, and S2O32- play key roles, suffices to give oscillatory behaviour. By extending this core set of reactions with additional steps that describe acid-base eq uilibria and reactions between H2O, and sulfur species, we obtain bett er agreement with the observed oscillatory behaviour as well as the ab ility 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 pe roxide oscillators should emphasize the capability of the sulfur subst rate to be partially oxidized to a relatively stable intermediate prio r to its total oxidation to sulfate.