Kinetics and mechanism of the reaction between thiosulfate and chlorite ions at 90°C

The kinetics of the oxidation of S 2 O 3 2− by ClO 2 − have been studied in aqueous alkaline solution at 90 0 C using classical titrimetric methods to follow the course of the reaction. The reaction takes place according to the stoichiometry S 2 O 3 2− + 2ClO 2 − + 2OH − = 2SO 4 2− + 2Cl − + H 2 O even in large S 2 O 3 2− excess. There is some indication of a complex reaction pattern, but 70% of the ClO 2 − disappearance can be best described by the autocatalytic rate equation ‐ d [ClO 2 − ]/ dt = k[S 2 O 3 2− ] [ClO 2 − ] [H + ] with k = (1.3 ± 0.2) ×10 8 M −2 sec −1 . The mechanism is explained by postulating nucleophilic attack of S 2 O 3 2− on HClO 2 to form a chlorine‐containing intermediate.