Chemistry of sodium dithionite. Part 1.—Kinetics of decomposition in aqueous bisulphite solutions

Abstract

The decomposition of sodium dithionite in concentrated bisulphite buffer solutions follows first-order kinetics with an activation energy of 18 kcal/mole. The rate is also first order in bisulphite ion, variable fractional order in hydrogen ion and shows zero salt effect. The reaction ˙HSO₂+˙SO^–₂+HSO^–₃→intermediate products (3) is proposed as the rate-determining step. Two sets of stable products, (½Na₂S₂O₃+NaHSO₃) and (Na₂S₃O₆), found in ratios between 9 : 1 and 1 : 1, probably result from common intermediates in reaction (3). These results are combined with those of hydrolysis to give a unified account of dithionite decomposition.