Kinetics and thermodynamics of the reaction of aliphatic N-bromamines with bromide ion in acid media, and the pKa of N-bromamines

The kinetics of the oxidation of bromide ions by aliphatic N-bromamines in aqueous acid media were studied using a pH jump technique. The reaction is first order in both bromide ion and total bromamine concentrations, and takes place only through the protonated N-bromamine. For two of the N-bromamines studied (N-Br-dimethylamine and N-Br-diethylamine), hydrolysis competed with the reaction with bromide ions, whereas in all the other cases hydrolysis was too slow to be detected. The pK(a) values obtained from the k(obs) vs. [H+] data at 25 degrees C are 2.88 for N-Br-dimethylamine, 3.24 for N-Br-diethylamine, 3.33 for N-Br-piperidine (all at I = 0.1 M), 2.26 for N-Br-isobutylamine and 2.92 for N-Br-sec-butylamine (both at I = 0.5 M).