Mechanism of the Hydrolysis of Endosulfan Isomers.

The objective of this study was to elucidate the mechanism of abiotic hydrolysis of ES isomers, i.e., Endosulfan-1 (ES-1) and Endosulfan-2 (ES-2), using a combination of experiments and density functional theory (DFT) calculations. Hydrolysis of both ES-1 and ES-2 resulted in the formation of Endosulfan Alcohol (ES-A). The rate of hydrolysis was first order in all cases and increased with both pH and temperature. Rate expressions describing the hydrolysis rates of ES-1 and ES-2 as a function of pH and temperature were obtained and validated with independent data sets. DFT calculations were performed using three functionals (M06-2X, B3LYP, and MPW1K) and both IEFPCM-UFF and SMD to introduce solvent effects. The geometry optimization of molecules ES-1 and ES-2 showed that the free energy of ES-1 was larger, and therefore, ES-2 was the more thermodynamically stable isomer. DFT calculations also supported a hydrolysis mechanism involving two successive attacks by OH