Dichloroacetonitrile formation from anthropogenic aromatic compounds during chlorination: Identification of structural characteristics and development of a predictive flowchart.

Dichloroacetonitrile (DCAN), a highly toxic nitrogenous disinfection byproduct, is of particular concern because of frequent detection in drinking water. Although natural precursors have been well characterized, the contributions of diverse anthropogenic aromatic compounds remain poorly understood. In this study, we systematically evaluated DCAN formation during the chlorination of 185 compounds, including 63 compounds selected from the list of the Japanese Pollutant Release and Transfer Register system and 122 nitrogenous aromatic compounds, to identify key structural features governing DCAN formation. These results demonstrated that aromatic amines and N-heterocycles were the primary precursors. Several compounds, such as m-phenylenediamine, exhibited molar yields exceeding those of well-known natural precursors such as amino acids. Specific structural moieties associated with high yields (>5%) were identified, including meta-diamino substitutions on the aromatic rings, para-amino substitutions on the pyridine rings, and an unsaturated C2-carbon in the five-membered N-heterocycles. Based on these findings, a practical flowchart was developed to qualitatively predict the DCAN yield categories (high/medium/low) and was applied to four structurally complex compounds (N-(1,3-dimethylbutyl)-N'-phenyl-1,4-phenylene diamine (6PPD), amodiaquine, indomethacin, and prilocaine). This illustrates the utility of the flowchart as a proactive screening tool for anthropogenic compounds with high DCAN formation potential, thereby supporting water quality management and risk assessment.