CHEMISTRY OF NITROSO-COMPOUNDS .11. NITROSATION OF AMINES BY THE 2-PHASE INTERACTION OF AMINES IN SOLUTION WITH GASEOUS OXIDES OF NITROGEN

The formation of secondary N-nitrosoamines when MeCN solutions of amines are brought into contact with gaseous NO, N2O3, and N 2O4 at 25 °C is reported. With NO, N-nitrosoamine formation from piperidine, morpholine, and diphenylamine occurs very slowly (t1/2 ca. 8 days). Reaction rates are largely independent of the amine, suggesting that oxidation of NO by adventitious oxygen is the slow step. Very much faster reactions are observed, however, with N2O3 and N2O4. With a ca. 10-fold excess of N2O 3 or N2O4, quantitative yields of both N-nitrosopiperidine and N-nitrosodiphenylamine are found in less than 3 min. With a 27-fold excess of piperidine and N2O4 only, ca. 8% N-nitropiperidine and 92% N-nitrosopiperidine are obtained. Rapid reactions also ensue when solutions of either primary aromatic or secondary amines dissolved in 0.1M-aqueous NaOH are brought into contact with gaseous N2O 3 and N2O4. With a ca. 2-400-fold excess of these nitrogen oxides, 12-65% of the amine is converted either to N-nitrosoamine or diazonium ion in less than 3 min. Competitive hydrolysis of the nitrogen oxide by the solvent is not HO--catalysed and the amine: H 2O reactivities are in ca. 1 000 : 1. The extent of N-nitrosation varies insignificantly over a wide range of basicities (pKa 11.12 to -1.0), but no reaction occurs with either 2,4-dinitroaniline or N-butyl-acetamide. With N2O4, smaller amounts of N-nitroamines form concurrently and increase with decreasing amine basicity. The results are discussed in relation to amine nitrosation by N2O 3 and N2O4 in aqueous acidic solutions. It is suggested that the lower selectivity for the dissolved gaseous reagents may relate to the presence of more reactive N2O3 and N 2O4 isomers. The results also show that carcinogenic N-nitrosoamines form under a much wider range of experimental conditions than previously known, some of which are relevant to atmospheric pollution.