KINETICS AND MECHANISM OF THE REACTION OF CHLOROUS ACID WITH CHLORATE IN AQUEOUS SULFURIC-ACID

Millimolar concentrations of chlorous acid in aqueous sulfuric acid (> 0.5 M) react in the presence of chlorate ions, producing chlorine dioxide, chloride ions, and chlorate ions. Reaction rates have been measured in terms of disappearance of chlorous acid and appearance of chloride and chlorine dioxide. All rates have apparent first-order dependencies with respect to chlorate concentration and Hammett acidity function. With regard to chlorous acid concentration, chloride and chlorous acid rates exhibit first-order dependence, while chlorine dioxide rate exhibits an order of 1.7. Catalysis by the chloride impurity in chlorate was experimentally ruled out as the cause of the rapid reaction rates we observed. A mechanism compatible with experimental observations involves chlorate acting as a catalyst in chlorous acid disproportionation, rather than acting as a reactant. Rate equations derived from the mechanism fit initial rate data with reasonable accuracy. Integrated equations derived from the mechanism predict chlorate and chlorine dioxide concentrations with reasonable accuracy at high chlorous acid conversion.