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Comparison of N-nitrosodimethylamine formation mechanisms from dimethylamine during chloramination and ozonation: A

Yong Dong Liu¹, Rugang Zhong¹

¹College of Life Science & Bioengineering, Beijing University of Technology, Beijing 100124, China.

Journal of Hazardous Materials

|September 20, 2016

Abstract:

N-nitrosodimethylamine (NDMA) as a disinfection by-product has recently become the focus of considerable research interest due to its unusually high carcinogenicity. In this study, the formation mechanisms of NDMA from dimethylamine (DMA) during chloramination and ozonation were investigated by using the quantum chemical G4 method. The reactivity of haloamines and hydroxylamine reacting with DMA was found in the order: NHCl₂∼NHBrCl (Br-leaving)>NHBr₂>NH₂Cl∼NH₂Br>>NH₂OH. This offers a theoretical support for the experimentally proposed mechanism that dimethylamine reacts with NHCl₂ rather than NH₂Cl to form chlorinated unsymmetrical dimethylhydrazine intermediate and the existence of bromochloramine in the presence of bromide during chloramination, and explains the observation that NDMA yield during ozonation is much lower than that during chloramination. Importantly, an N,N-dimethylaminonitrene was found to be a significant intermediate to form NDMA in oxidation reactions by molecular oxygen and ozone. Additionally, results suggest that the amines containing the second nitrogen source directly connecting or close to the N-(CH₃)₂ moiety are potential significant NDMA precursors upon ozonation. The findings of this study are helpful for expanding the knowledge of NDMA formation mechanism, and predicting potential NDMA precursors during disinfection.

Keywords:

Chloramination Dimethylamine G4 method N-nitrosodimethylamine Ozonation

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