A MULTICOMPONENT KINETICS STUDY OF THE ANAEROBIC DECOMPOSITION OF AQUEOUS SODIUM DITHIONITE

Multivariate analysis of aqueous attenuated total reflectance FTIR spectra has provided kinetic data for the anaerobic aqueous decomposition of the dithionite anion under mildly acidic conditions. All seven major components in solution were measured simultaneously in time resolved experiments covering a broad range of initial concentrations and temperatures. The experimental rate expressions from these studies result from three separate pathways, each with its own stoichiometry. Two of the pathways, one involving the heterolytic cleavage of S2O42- and the second its homolytic cleavage, dominate the decomposition process under high bisulfite concentrations. They are simultaneously competitive and consecutive, the first reaction producing the trithionate anion, a key reactant in the second reaction. The ionic strength dependencies of these pathways were measured over a 7-fold ionic strength range. A third pathway appears as the bisulfite ion concentration is lowered, becoming dominant at low [HSO3-](0). This pathway precedes and follows a very rapid, apparently autocatalytic decomposition.