Aromatic Structures\nGovern the Formation of Chlorinated\nByproducts in Dichlorine Radical Reactions

Radical-induced disinfection byproduct (DBP) formation\nis drawing\nattention with increasing applications of advanced oxidation processes\n(AOPs). Cl<sub>2</sub><sup>•–</sup> represents one of\nthe extensively generated radicals in AOPs, whose behavior in DBP\nformation remains unknown. In this study, we found that aromatic structures\nserve as the main DBP precursors in Cl<sub>2</sub><sup>•–</sup> reactions by employing diverse groups of model compounds. At a typical\nCl<sub>2</sub><sup>•–</sup> exposure of 1.2 × 10<sup>–9</sup> M·s, the sum concentrations of 7 regulated aliphatic\nDBPs (e.g., trichloromethane, chloroacetic acids) are ∼0.10\nto 0.48 μM for aromatic precursors and <0.05 μM for\naliphatic ones. The DBP formation mechanisms from Cl<sub>2</sub><sup>•–</sup> reactions involved the formation of chlorinated\naromatics, radical-induced oxygen incorporation followed by ring cleavage,\nand the interactions of Cl<sub>2</sub><sup>•–</sup> with\nring-cleavage intermediates. In reacting with DOM, Cl<sub>2</sub><sup>•–</sup> reactions produced much fewer aliphatic DBPs\n(5% of the total organochlorine vs 40% for chlorination) and chloroacetic\nacids dominated the aliphatic DBPs (usually trihalomethane for chlorination),\nwhich can be well interpreted by the precursors and mechanisms proposed.\nThis work comprehensively reveals the precursors, formation patterns,\nand mechanisms of DBPs during the less-studied Cl<sub>2</sub><sup>•–</sup> reactions, highlighting the importance of\neliminating the aromatic structures of DOM before the AOPs.