Revisiting the Kinetics and Mechanism of the Tetrathionate−Hypochlorous Acid Reaction in Nearly Neutral Medium†

The tetrathionate−hypochlorous acid reaction has been investigated in nearly neutral medium at I = 0.5 M ionic strength and T = 25.0 ± 0.1 °C in dihydrogen-phosphate−hydrogen-phosphate buffer by UV−vis spectrophotometry. In excess of hypochlorous acid, the stoichiometry was found to be S4O62− + 7HOCl + 3H2O → 4SO42− + 7Cl− + 13H+, but in excess of tetrathionate colloidal sulfur precipitates. On the basis of the simultaneous evaluation of the kinetic curves, a nine-step kinetic model with four fitted and five fixed rate coefficients is proposed. Analogous oxidation reactions of tetrathionate are also compared and discussed.