Cyanogen Bromide Formation from the Reactions of Monobromamine and Dibromamine with Cyanide Ion

Cyanide ion (CN-) was found to react with monobromamine (NH2Br) and dibromamine (NHBr2) according to the reactions NH2Br + CN- + H2O → NH3 + BrCN + OH- and NHBr2 + CN- + H2O → NH2Br + BrCN + OH- with respective reaction rate constants of 2.63 × 104 M-1 s-1 and 1.31 × 108 M-1 s-1. These values were found to be 105−106 times greater than those for the corresponding reactions between chloramine species and CN-. As a result, bromamines, even if present at relatively low concentrations, would tend to outcompete chloramines in reacting with CN-, and thus, the formation of BrCN would predominate that of ClCN through these reaction mechanisms. The NH2Br reaction was found to be general-acid-catalyzed. The third-order catalysis rate constants for H+, H2PO4 -, HPO4 2-, H3BO3, and NH4 + correlated linearly with their corresponding acid dissociation constants, consistent with the Brønsted−Pedersen relationship. The NHBr2 reaction did not undergo catalysis. A model was developed to predict the concentrations of bromamines over time on the basis of the above two reactions with CN- and bromamine formation/decomposition reactions previously reported.