Some effects of phenol- and thiol-nitrosation reactions on N-nitrosamine formation

C-Nitrosophenols, produced by the nitrosation of phenols, catalyse N-nitrosamine formation. The rate of N-nitrosation of pyrrolidine, catalysed by p-nitroso-o-cresol, is fastest at about pH 5. The catalytic species is thought to be the quinone monoxime tautomer of the nitrosophenol. A possible mechanism for the catalysis is proposed. A reaction of pyrrolidine with nitrite at pH 5.0 is described, which gives enhanced N-nitrosation in the presence of p-cresol. The yield of N-nitrosopyrrolidine (NPYR) is further enhanced when this reaction is carried out under anaerobic conditions. Nitrosocysteine hydrochloride reacts with N-methylaniline at pH 2.65, 5.5 and 9.75 in the absence of nitrite to give N-nitroso N-methylaniline. The N-nitrosation of morpholine and pyrrolidine at pH 9.75 is also effected by nitrosocysteine hydrochloride. The rate of N-nitrosation at this pH decreases with increasing amine basicity. The reaction of nitrosocysteine with N-methylaniline at pH 9.75 under anaerobic conditions leads to a significant reduction in the yield of N-nitroso-N-methylaniline.