Rate limiting electrophilic attack in nitrosation of aminoguanidine

摘要

Nitrosation reaction of aminoguanidine (AG) has been studied. The nitrosation rate is first-order with respect to both the AG and acid concentration. The absence of general base catalysis, the existence of catalysis by nucleophilic anions (X- and SCN-) and the observed inverse deuterium isotope effect lead us to propose a mechanism for AG nitrosation similar to that which operates in the case of amines, in which the electrophilic attack of the nitrosating agents is the rate determining step. From this mechanism, we were able to obtain the values of the rate constants for the nitrosation process. We have found that unlike the other amines, the protonated form of AG is the reactive species. This situation becomes possible for AG because protonation of guanidines occurs mostly on the iminic nitrogen, and this may be the reason for the lower reactivity of this amine.