Kinetics of the Rapid Base Catalyzed Iodination of Imidazole and 2-Methylimidazole by Molecular Iodine in Aqueous Medium: pH Effect

Abstract

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.