The reaction between BrO2- and excess HOCl (p[H+] 6-7, 25.0 degreesC) proceeds through several pathways. The primary path is a multistep oxidation of HOCl by BrO2- to form ClO3- and HOBr (85% of the initial 0.15 mM BrO2-). Another pathway produces ClO2 and HOBr (8%), and a third pathway produces BrO3- and Cl- (7%). With excess HOCl concentrations, Cl2O also is a reactive species. In the proposed mechanism, HOCl and Cl2O react with BrO2- to form steady-state species, HOClOBrO- and ClOClOBrO-. Acid facilitates the conversion of HOClOBrO- and ClOClBrO- to HOBrOClO-. These reactions require a chainlike connectivity of the intermediates with alternating halogen-oxygen bonding (i.e. HOBrOClO-) as opposed to Y-shaped intermediates with a direct halogen-halogen bond (i.e. HOBrCl(O)O-). The HOBrOClO- species dissociates into HOBr and ClO2- or reacts with general acids to form BrOClO. The distribution of products suggests that BrOClO exists as a BrOClO.HOCl adduct in the presence of excess HOCl. The primary products, ClO3- and HOBr, are formed from the hydrolysis of BrOClO.HOCl. A minor hydrolysis path for BrOClO.HOCl gives, BrO3- and Cl-. An induction period in the formation Of ClO2 is observed due to the buildup of ClO2-, which reacts with BrOClO.HOCl to give 2 ClO2 and Br-. Second-order rate constants for the reactions of HOCl and Cl2O with BrO2- are k(1)(HOCl) = 1.6 x 10(2) M-1 s(-1) and k(1)(Cl2O) = 1.8 x 10(5) M-1 s(-1). When Cl- is added in large excess, a Cl-2 pathway exists in competition with the HOCl and Cl2O pathways for the loss of BrO2-. The proposed Cl-2 pathway proceeds by Cl+ transfer to form a steady-state ClOBrO species with a rate constant of k(1)(Cl2) = 8.7 x 10(5) M-1 s(-1).