Photochemical transformations of 2, 6-dichlorophenol and 2-chlorophenol with superoxide ions in the atmospheric aqueous phase

The possible photochemical transformation pathways of chlorophenols (2, 6-dichlorophenol and 2-chlorophenol) with superoxide anion radical (O2·−) were studied by steady-state irradiation and 355 nm laser flash photolysis technique. O2·− was generated by irradiating riboflavin O2-saturated solution with an UVA light (maximum at 365 nm). The steady-state experimental results suggested that the transformation efficiency of chlorophenols improved with the increase of the initial riboflavin concentration and solution initial pH value, while the increase of chlorophenols concentration would inhibit the photochemical reaction. The second-order rate constant of the reaction of O2·− with 2, 6-DCP phenoxyl radical (2, 6-DCP·) and 2-CP phenoxyl radical (2-CP·) were determined as (8.39 ± 0.99) × 109 L mol−1 s−1 and (5.17 ± 0.68) × 109 L mol−1 s−1 by laser flash photolysis techniques, respectively. The transformation of chlorophenols was accompanied by the formation of Cl− induced by superoxide radicals after the mixed riboflavin and chlorophenols solution with UVA irradiation. The main conversion products of the reaction between 2, 6-DCP and O2·− were identified by GC-MS, as 2-chlorophenol, 2, 6-dichloro-1, 4-benzoquinone, 2, 6-dichloro-hydroquinone and 3-chlorocatechol, while 2-CP with O2·− was 2-chloro-1, 4-benzoquinone, 2-chlorohydroquinone and phenol, respectively. The transformation pathways of 2, 6-DCP and 2-CP with O2·− were also proposed.