As the primary degradation product of phthalate esters, phthalate monoesters (MPEs) have been widely detected in various aquatic environment and drawn growing toxicological concern. Hydrolysis mechanism and kinetics are of great importance for assessing the environmental behavior and persistence of MPEs. Nevertheless, how the nature of leaving group affects the hydrolysis mechanism and kinetics of MPEs is unclear. Herein, the mechanisms and kinetics of base-catalyzed and neutral hydrolysis for MPE anions with nine different leaving groups were investigated by density function theory (DFT) calculation and linear free energy relationship. Results indicate that the hydrolysis mechanism and kinetics for MPE anions are dependent on the nature of the leaving group. The smaller is the acidity constant of the leaving group, the faster is the base-catalyzed and neutral hydrolysis of MPE anions. Also, the DFT calculations show that MPE anions with good leaving groups prefer a more dissociative transition state. The half-lives of the investigated MPE anions were calculated and vary from 0.50 hours to 7.07 years (pH = 7~9), which is more persistent than its parent compounds. Results from this work lay the foundation for better understanding the chemical processes governing phthalate ester transformation in the aquatic environments.

Mechanism and kinetics of phthalate monoester hydrolysis

ACS Fall 2020 Virtual Meeting

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