Mechanism and kinetics of ClO[rad]-mediated degradation of aromatic compounds in aqueous solution: DFT and QSAR studies

Abstract

The action of ClO is more prominent than HO and Cl in the advanced oxidation degradation of some pollutants. However, studies on the pollutant degradation mechanism and kinetics by ClO are limited. In this study, 43 different kind of aromatic compounds which are important anthropogenic and natural water pollutants were selected as models to investigate their ClO oxidation mechanism and kinetics computationally. The results showed that radical adduct formation (RAF) rather than single electron transfer (SET) reaction was prominent in ClO-initiated reactions of aromatic compounds. In subsequent reactions of the ClO-adduct, the Cl end of the -OCl moiety shifted to the benzene ring, which was the key to hydroxylation and chlorination of aromatic compounds by ClO. The calculated ClO initiated reaction rate constants (kClO) of aromatic compounds were 102–1010 M−1 s−1. ClO was highly reactive to phenolates, anilines and alkoxy/hydroxyl aromatic compounds. Upon the deprotonation of phenol to phenolate, the kClO value increased by 4 orders of magnitude. The kClO values of alkoxybenzenes were higher for compounds with shorter alkyl side chains and more alkoxy substituents. The kClO increased for anilines with longer alkyl side chains. The kClO quantitative structure-activity relationships (QSARs) models were developed to predict the reactivity of ClO to complex aromatic compounds in aquatic systems.