ABSTRACT
The three 1,3-azoles, imidazole, thiazole and oxazole, are all very stable compounds which do autoxidise. Oxazole and thiazole are water-miscible liquids with pyridine-like odours. Amongst synthetic substances in use as therapeutic agents are Cimetidine, for the treatment of peptic ulcers, and Metrinidazole, an antiprotozoal, for example in the treatment of amoebic dysentry. Imidazole, thiazole and alkyloxazoles, though oxazole itself, form stable crystalline salts with strong acids, by protonation of the imine nitrogen, N-3, known as imidazolium, thiazolium and oxazolium salts. Imidazole, like water, is both a good donor and a good acceptor of hydrogen bonds; the imine nitrogen donates an electron pair and the N-hydrogen, being appreciably acidic, is an acceptor. Imidazoles with a ring N-hydrogen are subject to tautomerism, which becomes evident in unsymmetrically substituted compounds such as the methylimidazole shown. Friedel-Crafts acylations are unknown for the azoles, clearly because of interaction between the basic nitrogen and the Lewis acid catalyst.
