Kinetics and mechanism of the reaction between thiosulfate and chlorine dioxide

The reaction between thiosulfate and chlorine dioxide in slightly alkaline medium has been studied by stopped-flow techniques. The reaction cannot be studied under pseudo-first-order condition, thus a new approach based on the improved calibration and use of stopped-flow spectrophotometers was applied. The reaction starts with irreversible formation of . S2O3ClO22- radical. The main path of the reaction produces tetrathionate and chlorite through the formation of light absorbing tetrathionate radical (. S4O63-). Any of the reactant present in excess slightly modifies the 1:1 stoichiometry, and sulfate as well as chloride ions are also formed. A detailed mechanism based on a rigorous simultaneous fitting of the experimental data is proposed.