Mechanistic aspects of some nitrosation reactions
Mechanistic studies on a range of reactions involving both and N- and S-nitrosation have been performed. N-nitrosation reactions of diphenylamine, ammonia, dimethylamine, and hydrazine sulphate have been studied. As expected, the reactions were oatalysed by added nucleophiles. Possibly the most significant overall result from this study is that further evidence is provided which supports the theory that the encounter-controlled limit for the nitrosation of non=aromatic amines by NOX species, where X is a nucleophile, is approximately one hundred times lower than for aromatic amines. A kinetic study of the nitrosation of benzenesulphinic acid (BSA) has been carried out. The acidity dependence revealed that reaction with H(_2)NO(^+)(_2)/NO(^+), the nitrosyl halides or nitrosyl thiocyanate occurs via both the neutral acid molecule of BSA and its anion. The overall reactivity of benzenesulphinio acid towards nitrosation is very high, and it appears that the reaction of the sulphinate anion with H(_2)NO(^+)(_2)/NO(^+) is encounter-controlled. This high reactivity suggests that water soluble sulphinic acids may have potential use as nitrite traps, where it is important to remove nitrous acid quantitatively, rapidly and irreversibly. The ability of the nitrosothiosulphate anion to act directly as a nitrosating agent was also investigated, and compared directly with nitrosyl bromide and nitrosyl thiosulphate. It appears that this anion may act directly as a nitrosating agent, at least towards reactive substrates, and thus it represents an unusual example of a negatively charged electrophilic nitrosating agent. The mechanism of nitrosation of dimethyl sulphide has not been completely elucidated. However, it seems likely that a S-nitroso species is formed which apparently may act directly as a nitrosating agent.It is proposed that the mechanism of denitrosation of N-acetyl- S-nitroso-D, L-penicillamine in the presence of mercuric chloride occurs via the intermediacy of a mercury-sulphur complex.