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

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 M1 s1 at 27.0 degrees 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.