Cyanogen bromide formation from the reactions of monobromamine and dibromamine with cyanide ion

Cyanide ion (CN^-) was found to react with monobromamine (NH ₂Br) 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 CICN through these reaction mechanisms. The NH₂Br reaction was found to be general-acid-catalyzed. The third-order catalysis rate constants for H⁺, H₂PO ₄^-, HPO₄^2-, H₃BO ₃, 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.