Theoretical investigation on the oxidation mechanism of dibutyl phthalate by hydroxyl and sulfate radicals in the gas and aqueous phase

A thorough thermodynamic analysis of different DBP conversion paths induced by hydroxyl (OH) and sulfate radicals (SO4−) is performed using Density Functional Theory (DFT) calculations in the gas and aqueous phases. We propose the thermodynamics favorable reaction chains for the major degradation products formation, and the involved reaction mechanisms include radical adduct formation (RAF), formal hydrogen atom transfer (FHAT), OH oxidative cleavage of CC double bond, and acid-catalyzed decomposition of C-C single bond. Theoretical results indicate that phthalic anhydride (PA) and acetophenone (ACP) are respectively the dominant and minor products in water, which is consistent with the experimental data. Computational results reveal that the reactivity of OH for the H-abstraction reaction is higher than that of SO4−. Interestingly, the unsaturated CC bonds cleavage reaction can directly occur with OH attack in aqueous solutions. However, it needs to overcome an extra radical adduct formation step when it is attacked by SO4−. The present work opens a new window to illustrate the reaction mechanism and reactivity of OH and SO4− toward different chemical structures of organics from the view of molecular level.