| Abstract
| - On the basis of stopped-flow spectrophotometric studies, a detailed mechanism is proposed for the oxidation of the chlorite ion by elementary bromine. It is shown that the oxidation proceeds via competing parallel reaction steps with Br2, Br2-, Br, and HOBr as oxidants.
- The kinetics and mechanism of the chlorine(III)−bromine reaction are studied by the stopped-flow method underacidic conditions in 1.0 M NaClO4 and at 25.0 °C. There are two kinetically well-separated phases in this reaction.A detailed mechanism is proposed for the first phase of the reaction, in which Br2 oxidizes ClO2- to chlorinedioxide. It is confirmed that the oxidation occurs via competing parallel reaction steps. The autoinhibition observedin the reaction is attributed to a backward shift in the reversible initial step as the oxidation proceeds. On thebasis of simultaneous evaluations of the kinetic traces, the following forward rate constants are obtained for thekinetically significant reaction steps: Br2 + ClO2- ⇌ ClO2 + Br2-, k1 = (1.3 ± 0.2) × 103 M-1 s-1 (k-1 = 1.1× 109 M-1 s-1); Br2- + ClO2- = ClO2 + 2Br-, k2 = (4.0 ± 0.1) × 106 M-1 s-1; Br + ClO2- = ClO2 + Br-,k8 = (2.3 ± 0.7) × 108 M-1 s-1; HOBr + HClO2 = BrClO2 + H2O (BrClO2 + ClO2- = Br- + 2ClO2, veryfast), k9 = (1.9 ± 0.1) × 105 M-1 s-1. The possible kinetic role of the reactive BrClO2 intermediate is discussedin detail.
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