KINETICS OF REACTIONS OF CHLORINE DIOXIDE (OCLO) IN WATER .2. QUANTITATIVE STRUCTURE-ACTIVITY-RELATIONSHIPS FOR PHENOLIC-COMPOUNDS

Chlorine dioxide (OClO) rapidly oxidizes substituted phenoxide anions in aqueous solution and second-order rate constants for this reaction have recently been reported for 25 compounds. Analysis of these data f or correlations reveals several quantitative structure-activity relati onships (QSARs) that can be used to predict rate constants for the rea ction of additional phenolic compounds with chlorine dioxide. The rate constants for oxidation of phenoxide anions give good Hammett correla tions to sigma- constants and Marcus correlations using half-wave oxid ation potentials. Ortho- as well as meta- and para-substituted phenoxi des have been included in both types of correlations and the only outl iers are compounds that exhibit strong intramolecular hydrogen bonding . The results of the Marcus correlation analysis are consistent with t he expected mechanism of reaction where the rate-limiting step is sing le electron-transfer from the phenoxide anion to chlorine dioxide. The second-order rate constants for oxidation of the undissociated forms of substituted phenols are about six orders of magnitude smaller than the corresponding values for phenoxide anions, indicating that only th e reaction of phenoxide anions will be significant under the condition s of water treatment with chlorine dioxide. The rate constants for und issociated phenols also have much greater relative uncertainties than those for the phenoxide anions, and give much less satisfactory correl ations.