A Quantitative Structure–Reactivity Assessment of Phenols by Investigation of Rapid Iodination Kinetics Using Hydrodynamic Voltammetry: Applicability of the Hammett Equation in Aqueous Medium


  • This paper is dedicated to Professor Dr. T. S. Rao on the occasion of his 82nd birthday, in recognition of his outstanding contributions to chemical kinetics, especially rapid kinetics in aqueous medium.

Correspondence to: Vijay T. Dangat; e-mail: vijaydangat@gmail.com.


Halogenations of aromatic substrates in aqueous medium are essentially electrophilic substitutions proceeding at rates concomitant with the nature of the substrates and substituent motifs. Kinetics as an investigatory tool for the quantitative assessment of the structure–reactivity correlation in these reactions for a diverse range of substrates has rarely been reported, presumably due to the rapidity of these reactions in aqueous medium. We have used hydrodynamic voltammetry to investigate the rapid kinetics of uncatalyzed iodination of phenol and eight substituted phenols by iodine monochloride at constant pH in aqueous medium. The Arrhenius plots for these reactions yield comprehensive kinetic and thermodynamic data. The quantitative structure–reactivity correlation stemming from the regio- and stereospecificity of the substituent motifs on the substrates has been examined through the Hammett plot, which shows a negative slope of 1.87. The magnitudes of the rate constants, energies of activation, frequency factors, and entropy change obtained for the nine fast reactions reported, reflect the relative ease of the reaction dynamics in quantitative terms thereby ascertaining the relative reactivities of the phenols studied herein.