Role of Carbonyl Compounds for <i>N</i>-Nitrosamine Formation during Nitrosation: Kinetics and Mechanisms
Yishuai Pan, Florian Breider, Benjamin Barrios, Daisuke Minakata, Huiping Deng, Urs von Gunten
Abstract
High Resolution Image Download MS PowerPoint Slide 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.