Kinetics and mechanism of the reaction between hypochlorous acid and tetrathionate ion

The reaction has been studied spectrophotometrically monitoring the absorbance in the 240–400 nm wavelength range. The spectra of the reactants, intermediates, and products in this system are overlapping; thus special programs 1 , 2 ] have been used (and tested) to unravel the kinetics and mechanism of the reaction. The stoichiometry of the reaction in excess hypochlorous acid is S₄O₆²⁻ + 7HOCl + 3H₂O → 4SO₄²⁻ + 7Cl⁻ + 13H⁺. Various experiments are presented to show that—in excess tetrathionate—the reaction produces a light‐absorbing intermediate identified as S₂O₃Cl⁻. The intermediate slowly hydrolyzes into sulfur and sulfate and it yields pentathionate in excess tetrathionate. The rate‐determining steps and their rate constants are The further oxidation of S₂O₄²⁻ and SO₃²⁻ by HOCl to sulfate are fast processes. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 395–402, 2000