Formation Mechanisms of Nitro Products from Transformation of Aliphatic Amines by UV/Chlorine Treatment
Zhechao Hua, Jieying Liang, Ding Wang, Zhihong Zhou, Jingyun Fang
Abstract
Formation of nitrogenous disinfection byproducts from aliphatic amines is a widespread concern owing to the serious health risks associated with them. However, the mechanisms of transforming aliphatic amines and forming nitro products in the UV/chlorine process have rarely been discussed, which are investigated in this work. Initially, secondary amines (R 1 R 2 NH) are transformed into secondary organic chloramines (R 1 R 2 NCl) via chlorination. Subsequently, radicals, such as HO• and Cl•, are found to contribute predominantly to such transformations. The rate constants at which HO•, Cl•, and Cl 2 •– react with R 1 R 2 NCl are (2.4–5.1) × 10 9, (1.5–3.8) × 10 9, and (1.2–6.1) × 10 7 M –1 s –1, respectively. Consequently, R 1 R 2 NCl are transformed into primary amines (R 1 NH 2 /R 2 NH 2 ) and chlorinated primary amines (R 1 NHCl/R 2 NHCl and R 1 NCl 2 /R 2 NCl 2 ) by excess chlorine. Furthermore, primarily driven by UV photolysis, chlorinated primary amines can be transformed into nitroalkanes with conversion rates of ∼10%. Dissolved oxygen and free chlorine play crucial roles in forming nitroalkanes, and post-chlorination can further form chloronitroalkanes, such as trichloronitromethane (TCNM). Radicals are involved in forming TCNM in the UV/chlorine process. This study provides new insights into the mechanisms of transforming aliphatic amines and forming nitro products using the UV/chlorine process.