Kinetic and mechanistic study of ozonation of three dichlorophenols in aqueous solutions

This research investigates the kinetic parameters associated with the ozona tion of 2,3-, 2,4-, and 2,5-dichlorophenols (DCPs) in aqueous solutions at 25 degrees C. The overall ozonation kinetics of each DCP was found to be fi rst order with respect to each reactant concentration (i.e., DCP and ozone) . Among the three isomers studied, the ozonation of 2,5-DCP was the fastest with the overall rate constant varying from 68,500 to 7,750,000 M-1 s(-1) within a pH range of 2.1 to 5.0. The overall rate constant increased with p H because of the increase in the degree of dissociation of the DCP molecule s to dichlorophenoxide ions. The electrophilic addition of ozone at the ort ho and para positions of the molecular and ionic forms of the DCPs was post ulated to be the likely mechanism for the degradation of the DCPs to chloro benzenediols, monochlorophenols, chlorocyclohexadienediones, ethylacetate, heptanone, carboxylic acids, and other by-products that were detected using gas chromatograph/mass spectrometry analysis.