Abstract
Reaction between chlorine(III) and bromine results in the oxidation of chlorine(III) to chlorine dioxide according to 2C102" (or 2HC102) + Br2 — 2C102 + 2Br (+ 2H+) (reaction A). The kinetics of reaction A were studied by stopped-flowspectrophotometry in the pH range 0.58-4.23, leading to a proposed mechanism in which the rate-determining step is BrC102 + C102" (or HC102) — 2C102 + Br" (+ H+) (reaction B). The rate data obtained at 25 °C and ionic strength 0.66 M yield the rate constant of reaction B, kB = (2.94 ± 0.25) X 103 NT1 s"1, and the acidity constant of the intermediate BrC102H+, K, = (1.23 ± 0.02) X 10"2 M. At pH 7.41 bromine is present as BrOH and Cl(III) as C102~. Consequently the rate constant for the reaction between BrOH and C102~, 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.