Photochemical oxidation of o-dichlorobenzene in aqueous solution by hydroxyl radicals from nitrous acid

Abstract

The mechanism and kinetic parameters of the photochemical reaction of o-dichlorobenzene (o-DCB) in the presence of nitrite were studied by steady-state irradiation and laser flash photolysis. The degradation efficiency of o-DCB was observed to be influenced by N(III) (H2ONO+, HONO, NO2−) concentration, initial concentration of o-DCB and pH value. The hydroxyl radicals generated by the photolysis of N(III) attacked the benzene ring of o-DCB to form an o-DCB-OH adduct with the second-order reaction rate constant of (2.69 ± 0.3) × 109 L mol−1 s−1. Subsequently, the o-DCB-OH adduct reacts with molecular oxygen, NO2, H2ONO+ and HONO with rate constants of (1.28 ± 0.3) × 108 L mol−1 s−1, (1.5 ± 0.4) × 108 L mol−1 s−1, (1.3 ± 0.2) × 107 L mol−1 s−1 and (1.0 ± 0.3) × 107 L mol−1 s−1, respectively. The main products of the OH-initiated reaction of o-DCB were identified by gas chromatograph and mass spectrometer (GC–MS) to be o-chlorophenol, 2-chloro-3-nitrophenol, 1,2-dichloronitrobenzene, 2,3-dichlorophenol, 2,3-dichloro-1,4-benzoquinone and 2,3-dichloro-4-nitrophenol and the reaction mechanism leading to these products is discussed.