Chlorination mechanism of benzene series in aqueous system under the combined action of Cl- and multiple free radicals

Abstract

In this study, non-targeted analysis revealed that the Fe2+/perodisulfate/Cl- system degraded aniline (AN) and nitrobenzene (NB), yielding 7 types and 4 types of aromatic chlorides, respectively. In order to explore their chlorination mechanism and the influence of different functional groups, various reactions (radical adduct formation (RAF), hydrogen atom abstraction (HAA) and single electron transfer (SET)) of benzene series with various functional group with sulfate radical (SO4·-), hydroxyl radical (·OH), chlorine radical (·Cl) and dichloride anion radicals (Cl2·-) were explored by Gibbs free energy (ΔG), and the subsequent reactions of SET and HAA products (organic free radical) were innovatively explored by ΔG. This study revealed that the reaction between benzene compounds containing electron-donating groups and ·Cl was dominated by HAA rather than RAF; the reaction between benzene compounds containing electron-withdrawing groups and ·Cl was dominated by RAF. Aromatic compounds containing electron-donating groups can undergo SET reaction and generate aromatic chlorides in the presence of O2 and Cl-. Combined with the product analysis, it was found that the HAA reaction of aromatic compounds will lead to the obvious formation of biphenyl compounds and aromatic chlorides in the presence of Cl-. Compared with the conditions of RAF of ·Cl and chlorination of SET products, the chlorination reaction between HAA products and Cl- is ubiquitous, which is more likely to be the key to the formation of aromatic chlorides in mixed systems. This study provides a theoretical basis for further study on the formation risk of chlorinated products in advanced oxidation process.