Kinetics and Mechanism of the Reaction between Chlorine(III) and Molecular Bromine

Article abstract of DOI:10.1021/j100283a022

Reaction between chlorine(III) and bromine results in the oxidation of chlorine(III) to chlorine dioxide according to 2ClO2^- (or 2HClO2) + Br2 -> 2ClO2 + 2Br^- (+ 2H⁺) (reaction A).The kinetics of reaction A were studied by stopped-flow spectrophotometry in the range 0.58-4.23, leading to a proposed mechanism in which the rate-determining step is BrClO2 + ClO2^- (or HClO2) -> 2ClO2 + Br^- (+ H⁺) (reaction B).The rate data obtained at 25 deg C and ionic strength 0.66 M yield the rate constant of reaction B, k_B = (2.94 +/- 0.25) * 10³ M^-1 s^-1, and the acidity constant of the intermediate BrClO2H⁺, K_a = (1.23 +/-0.02) * 10^-2M.At pH 7.41 bromine is present as BrOH and Cl(III) as ClO2^-.Consequently the rate constant for the reaction between BrOH and ClO2^-, 20.6 M^-1 s^-1, indicates that BrOH is less reactive than Br2 toward Cl(III).Formation of the intermediate is a complex process involving attack by chlorine(III) on molecular bromine followed by electron transfer and leaving of bromide ion.