Chemistry of nitroso-compounds. Part 16. Formation of N-nitrosamines from dissolved NOCl in the presence of alkanolamines and related compounds

Abstract

The formation of carcinogenic N-nitrosamines (e.g. N-nitrosopiperidine) from dissolved NOCl gas in the presence of eight alkanolamines (triethanolamine, diethanolamine, N-methylethanolamine, N,N-diethylethanolamine, N-acetylethanolamine, N-nitrosodiethanolamine, N-methyl- N-nitrosoethanolamine and choline chloride) and secondary amines in aqueous solution (usually 0·1 m-NaOH) at 25°C is reported. In the absence of alkanolamines and with an approximately sixfold excess of NOCl, about 35% of the amine is converted into N-nitrosamine in less than 3 min. In the presence of alkanolamines, the reactions are slower but often much more extensive. With 0·05 m- N-nitrosodiethanolamine (the best promotor examined) about 85% of 2 × 10 −3 m-piperidine in 0·1 m-NaOH at 25°C is converted to N-nitrosopiperidine in 38 min by a sixfold excess of NOCl. These reactions are considered to proceed via an alkyl nitrite intermediate generated from the alkanolamine and the NOCl, which then nitrosates the secondary amine in a rate-limiting step. The most reactive intermediates derive from alkanolamines bearing strong electron-withdrawing substituents. Similar reactions are observed with N 2O 4 in place of NOCl, and it is suggested that in this way, NO x pollutants may contribute to the formation of N-nitrosamines in consumer products containing alkanolamines as emulsifiers.