摘要
Understanding the molecular mechanisms behind the formation of unregulated nitrogenous disinfection by-products (N-DBPs), such as dichloroacetonitrile (DCAN) and dichloroacetamide (DCAcAm), during chloramination of various dissolved organic nitrogen compounds—particularly free amino acids (AAs)—is critical for elucidating their formation fate and mitigating their occurrence in treated water. This study offers computational and experimental insights into the formation potential and mechanisms of DCAN/DCAcAm from distinct precursors. The experiments reveal a clear trend in DCAN formation potential: Asparagine (Asn) > aspartic acid (Asp) > β -alanine ( β -Ala) ≈ 4 - amino-2-hydroxybutyric acid (AHBA) > > alanine (Ala), aligning well with computed reaction energetics. The computations highlight a novel “one-step chlorination + decarboxylation” mechanism that may kinetically dominate the formation of DCAN and its hydrolysate DCAcAm from Asp and Asn at low NH 2 Cl levels, while higher concentrations of NH 2 Cl promote DCAN formation via the “aldehyde” pathway. Notably, Asn chloramination preferentially generates DCAcAm via multistep transformation from an aldehyde-based intermediate, enhancing its overall yield. By contrast, both β -Ala and AHBA form DCAN via a two-step N -chlorination pathway, owing to the absence of C α −COO - . The application of 15 NH 2 Cl to Asp and Asn further confirms NH 2 Cl as the primary nitrogen donor for DCAN formation at high [NH 2 Cl]/[org-N] ratios, whereas β -CONH 2 in Asn predominantly contributes to DCAcAm nitrogen. Mechanistically, electron-withdrawing groups at the C α and C β sites of precursors synergistically activate the C α −C β bond, facilitating DCAN/DCAcAm formation. Accordingly, removing the precursors with R , R' -CH-NH 2 groups effectively reduces DCAN/DCAcAm levels during water chloramination disinfection.
危险品化学品经营许可证（带存储）