88] Acyl imidazoles

Abstract

Publisher Summary This chapter discusses the synthesis and properties of acyl imidazoles. Under Schotten–Baumann conditions, imidazoles generally undergo ring opening; for example, the reaction of imidazole with benzoyl chloride in sodium hydroxide solution yields dibenzoyl diaminoethylene and formic acid. However, in the instance of a few substituted imidazoles, the reaction has been noted to yield the N-acyl derivative. This cleavage reaction, known as the Bamberger reaction, is remarkable in view of the general stability of the imidazole nucleus. Imidazoles may be acylated by the reaction of one mole of an acid chloride with two moles of the imidazole compound. The recent finding that imidazole hydrochlorides are readily acylated by anhydrides to yield the corresponding N -acyl imidazole hydrochlorides has led to the most satisfactory synthesis of the unstable N -acyl imidazoles. Imidazoles catalyze the hydrolysis of esters formed from alcohols that are reasonably strong acids. Both the neutral imidazole and the imidazole anion are catalysts, but the positive imidazolium ion is not. For the imidazole-catalyzed hydrolysis of p -nitrophenyl acetate, it has been shown that N -acetylimidazole accounts quantitatively, as an intermediate, for the conversion of the ester to hydrolytic products.