The second‐order kinetics of iodination of imidazole and 2‐methylimidazole in aqueous medium at various pH values and temperatures are studied in the presence and absence of a base catalyst. The reactions being electrophilic substitutions, molecular iodine is the sole iodinating agent, as the reactant solutions used are totally devoid of I− ions. The specific reaction rates of imidazole (I) and 2‐methylimidazole (II) for the catalyzed reactions are found to be 87.00 and 62.92 M−1 s−1 at 27.0°C, respectively, at 7.0 pH. The base component of the buffer used to maintain the pH catalyzes the reactions. The rapidity of the reactions necessitates the use of a rotating platinum electrode to follow the decay of the unreacted iodine. The study provides a quantitative verification of the reactivities of the substrates.

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.

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