Kinetics, stoichiometry and mechanism in the bromination of aromatic heterocycles. II. Aqueous bromination of imidazole, 1-methylimidazole and 2-methylimidazole

Abstract

The coulo-chrono-potentiometric method has been used to obtain rate constants for reaction of molecular bromine with neutral imidazoles (aq., 298 K). Values of 10^-6_kbl/dm³ mol^-1 s^-l were: Substrate 5-position 4-position 2-position Imidazole 0.5 0.4 0.2 1-Methylimidazole 2.3 1.7 0.8 2-Methylimidazole 90 - - The network of reactions leading to 2,4,5-tribromo-1-methylimidazole is described in detail. Relative rates of successive brominations are pH sensitive and conditions may be designed to obtain optimum yields of partially brominated imidazoles.