Abstract

Bromide ion is rapidly converted to HOBr via BrCl by reaction with HOCl. The subsequent slow reactions of (HOCl, OCl⁻)/(HOBr, OBr⁻) mixtures are monitored directly by multiwavelength UV–vis absorbance methods and simultaneously by ion chromatographic measurement of ClO₂⁻, ClO₃⁻, and BrO₃⁻ (p[H⁺] 5.6–7.6). A first-order loss of HOCl is observed which is catalyzed by trace concentrations of Br⁻ and BrCl. Chlorite ion forms first and is subsequently oxidized to ClO₃⁻. The loss of HOBr is slower and is second-order in HOBr, so that BrO₃⁻ formation takes longer than ClO₃⁻ formation. Under the conditions of this work, the relative yield of BrO₃⁻ increases with increase in pH. The decomposition of HOCl by bromide proceeds primarily by a series of halogen(I) cation-transfer reactions with subsequent halide release. The presence of HOCl increases the BrO₃⁻ yield three-fold from HOBr decay alone.