Kinetics of chlorination of phenol and monosubstituted phenols by t-butyl hypochlorite in aqueous alkaline medium

Abstract

The kinetics of chlorination of the parent and sixteen monosubstituted phenols (2-chloro, 2-methyl, 2-carboxy, 2-nitro, 3-chloro, 3-methyl, 3-carboxy, 4-fluoro, 4-chloro, 4-bromo, 4-methyl, 4-ethyl, 4-methoxy, 4-carboxy, 4-acetyl and 4-nitro) by t-BuOCI have been studied in aqueous alkaline medium. The rates of reactions show first order kinetics each in [t-BuOCl] and [XC 6 H 4 OH] and inverse first order in [OH - ]. Variation in either ionic strength or addition of reaction product has no significant effect on the rates of reactions, while lowering of the dielectric constant of the medium increases the rate. The rates are measured at different temperatures and the activation parameters for all the phenols computed. A mechanism involving the electrophilic attack of phenoxide ions by HOCl in the rate determining step is suggested. The rates decrease in the order : 3-CH 3 > 2-CH 3 > 4-OCH 3 > 4-CH 3 > 4-C 2 H 5 > H > 3-Cl > 3-COO - > 4-F > 2-COO - > 4-Br > 2-Cl > 4-Cl > 4-COO - > 4-COCH 3 > 2-NO 2 > 4-NO 2 . Hammett equation of the type, log k = -3.44 - 2.35 p is found to be valid for substituent effects. The enthalpy and entropy of activation are correlated.