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 (k 1.0) M-' min-' . Above pH 5 , hydrolysis is independent of pH, with a rate constant of 1.02 (t0.12) x IOW4 min-' at 25°C. In natural waters, the hydrolysis rate constant of CSO had an average value of 0.59 (k0.12) x IOW4 min-I. In sediment-associated water, the observed rate constant was 1.70 (k0.05) x 10-min-' . 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 l-(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.