Prediction model on hydrolysis kinetics of phthalate monoester: A density functional theory study

As primary degradation products of phthalate esters, phthalate monoesters (MPEs) have been widely detected in various aquatic environments and drawn growing toxicological concerns. Hydrolysis kinetics that is of importance for assessing environmental persistence of chemicals remain elusive for MPEs. Herein, kinetics of base-catalyzed and neutral hydrolysis for 18 MPEs with different leaving groups was investigated by density functional theory calculation. Results indicate that MPEs with leaving groups having pK_a of <10 prefer dissociative transition states. MPEs are more persistent than their parents, and their hydrolysis half-lives were calculated to vary from 3.4 min to 79.2 years (pH = 7-9). A quantitative structure-activity relationship model was developed for predicting the hydrolysis kinetics parameters. It was found that pK_a of the leaving groups and electronegativity of the MPEs are key factors determining the hydrolysis kinetics. This work may lay a theoretical foundation for better understanding the chemical process that governs MPE persistence in aquatic environments.