Role of Carbonyl Compounds for N -Nitrosamine Formation during Nitrosation: Kinetics and Mechanisms.

N -Nitrosamines are potential human carcinogens frequently detected in natural and engineered aquatic systems. This study sheds light on the role of carbonyl compounds in the formation of N -nitrosamines by nitrosation of five secondary amines via different pathways. The results showed that compared to a control system, the presence of formaldehyde enhances the formation of N -nitrosamines by a factor of 5-152 at pH 7, depending on the structure of the secondary amines. Acetaldehyde showed a slight enhancement effect on N -nitrosamine formation, while acetone and benzaldehyde did not promote nitrosation reactions. For neutral and basic conditions, the iminium ion was the dominant intermediate for N -nitrosamine formation, while carbinolamine became the major contributor under acidic conditions. Negative free energy changes (<-19 kcal mol -1 ) and relatively low activation energies (<18 kcal mol -1 ) of the reactions of secondary amines with N 2 O 3 , iminium ions with nitrite and carbinolamines with N 2 O 3 from quantum chemical computations further support the proposed reaction pathways. This highlights the roles of the iminium ion and carbinolamine in the formation of N -nitrosamines during nitrosation in the presence of carbonyl compounds, especially in the context of industrial wastewater.