Hydrolysis of chlorostilbene oxide: I. Hydrolysis in homogeneous systems

Abstract

The hydrolysis kinetics of 4-chlorostilbene oxide (CSO) in buffered distilled water, in natural waters and in sediment-associated water are reported. The disappearance of CSO followed pseudo-first-order kinetics in buffered distilled water over the experimental pH range of 3 to 11. Below pH 5, acid-catalyzed hydrolysis dominates, with a second-order rate constant of 11.3 (±1.0) M−1 min−1. Above pH 5, hydrolysis is independent of pH, with a rate constant of 1.02 (±0.12) × 10−4 min−1 at 25°C. In natural waters, the hydrolysis rate constant of CSO had an average value of 0.59 (±0.12) × 10−4 min−1. In sediment-associated water, the observed rate constant was 1.70 (±0.05) × 10−4 min−1. Sorption of CSO to the humic materials in natural waters and biotic effects in sediment-associated water appropriately explain the differences from sterile buffer solutions. Buffer catalysis was observed, but on the other hand, a negative ionic strength effect was determined. The formation of diastereoisomers of 1-(4-chlorophenyl)-2-phenylethylene glycol as major products at both acidic and neutral pH values suggests that CSO undergoes acid-catalyzed as well as neutral hydrolysis reactions through an A-1 carbonium ion mechanism. The rate constant for hydrolysis of CSO at pH 14 is only 70% faster than the hydrolysis rate constant over the pH range of 5 to 11, which suggests that nucleophilic addition of hydroxide ion is not the main hydrolytic mechanism of CSO hydrolysis at high pH values.