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

摘要

Cyanide ion (CN~-) was found to react with monobromamine (NH_2Br) and dibromamine (IMHBr_2) according to the reactions NH_2Br + CN~- + H_2O - NH_3 + BrCN + OH-and IMHBr_2 + CN~- + H_2O - NH_2Br + BrCN + OH~- with respective reaction rate constants of 2.63 x 10~4 M~(-1) s~(-1) and 1.31 x 10~8 M~(-1) s~(-1) These values were found to be 10~5-10~6 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 NH_2Br reaction was found to be general-acid-catalyzed.The third-order catalysis rate constants for H~+,H~2PO~4~-,HPO_4~(2-),H_3BO_3,and NH_4~+ correlated linearly with their corresponding acid dissociation constants,consistent with the Br0nsted-Pedersen relationship.The NHBr_2 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.