Bromamine decomposition kinetics in aqueous solutions.

The objectives of this study are to investigate the kinetics of bromamine decomposition and to identify the corresponding relevant reactions. Experiments were performed with a stopped-flow spectrophotometer system. Experimental variables investigated included pH (6.5-9.5), bromamines concentration (0.15-0.50 mM), ammonia to bromine ratio (5-100), and phosphate and carbonate buffers concentration (5-40 mM). The experimental results were consistent with a reaction scheme that involved the reversible disproportionation of monobromamine into dibromamine and ammonia (2NH2Br (k1)<=>(k(-1)) NHBr2 + NH3), followed by irreversible decomposition of monobromamine and dibromamine into products (2NHBr2 (k2) --> products and NH2Br + NHBr2 (k3) --> products). The monobromamine disproportionation reaction was found to undergo general acid catalysis, and the two subsequent decomposition reactions were found to experience base catalysis. Experimental results were analyzed for the determination of catalysis terms corresponding to H+, NH4+, H2PO4-, HCO3-, and H2O for rate constants k1 and k(-1); HPO4(2-) and H2O for k2; and OH-, CO3(2-), and H2O for k3. These constants were fitted with the Brønsted relationship, and the resulting fitting expressions were used to calculate any relevant catalysis rate constants that could not be determined at the range of experimental conditions used.