Kinetics of the reaction between hydrogen peroxide and hypobromous acid: Implication on water treatment and natural systems

Abstract

HOBr can be formed in various oxidation processes in engineered and natural systems. The rate of HOBr reduction by H 2O 2 is decisive to avoid formation of brominated organic compounds and bromate during ozone or hydrogen peroxide-based advanced or naturally occurring oxidation processes. From the pH dependence of this rate that was determined by stopped-flow measurements we conclude that either OBr − and H 2O 2 or HOBr and HO − 2 react with each other. Assuming that either one of the reactions takes place the corresponding second-order rate constants were determined to be k OBr −·H 2O 2 = (1.2 ± 0.2)·10 6M −1s −1 and k HOBr·HO − 2 = (7.6 ± 1.3)·10 8M −1s −1. Mechanistic considerations lead to the conclusion that a nucleophilic attack of HO − 2 on HOBr must be the dominant reaction in the system. From the determined rate constants it can be estimated that the half-life for HOBr is less than a few seconds for a H 2O 2 concentration of 0.1 mg L −1 (3 μM) at pH 8. However, at a lower pH of 5, as encountered in cloud waters, the half-life of HOBr is several hours for the same H 2O 2 concentration.