Photochemical reaction mechanism of 4-chloro-2-aminophenol and superoxide ions
摘要
4-Chloro-2-aminophenol (4C2AP) is a toxic and carcinogenic priority pollutant used in the chemical and pharmaceutical industries. This study explored the photochemical reaction between 4C2AP and superoxide anion radicals (O2•−) in the atmospheric aqueous phase. O2•− was produced by irradiating riboflavin (RF)/O2 solution with 365 nm ultraviolet light. The results showed that the conversion efficiency of 4C2AP increased with the increase of solution pH and RF concentration, but decreased with elevated pollutant concentration. The second-order rate constant for the reaction between O2•− and the 4C2AP phenoxy radical was determined to be (9.12 ± 0.75) × 109 L mol−1 s−1 by laser flash photolysis technique. Upon UVA irradiation of a RF/4C2AP mixture solution, the transformation of chlorophenol was accompanied by Cl− release, a process mediated by O2•−. GC–MS analysis indicated that the main products were 2-amino-1, 4-benzoquinone (2ABQ), 2-aminohydroquinone (2AHQ), and 2-aminophenol (2AP). The reaction mechanism involved two pathways: nucleophilic attack on C–Cl bond leading to dechlorination, and addition to phenoxyl radical forming intermediate adducts, with the latter being the dominant route. This work would provide a theoretical insight into the environmental behavior of chlorophenol pollutants in the atmosphere.