KINETICS OF THE ENOLIZATION REACTIONS OF 2-ACETYLPYRROLE AND OF 2-ACETYLTHIAZOLE, 4-ACETYLTHIAZOLE AND 5-ACETYLTHIAZOLE

Kinetic results are reported on the rates of enolisation of title comp ounds in water, in acetate buffers, in dilute hydrochloric acid, in di lute sodium hydroxide solutions and in the presence of several metal-i on salts, as measured by their rates of halogenation at 25 degrees C. The results have been compared with those previously obtained from the corresponding reactions of acetophenone and a number of acetylheteroc ycles. It is shown that a suitable metal cation (e.g., Cu2+) can be hu ndreds of times more effective than the proton in catalysing the enoli sation process of an acetylheterocyclic compound. This can be due eith er to the 'soft' character of the acetyl group, as, for example, that of 2-acetylpyrrole, or to coordination of both the carbonyl oxygen and the heteroatom by the metal cation in the transition state of the rea ction, as for 2- and 4-acetylthiazoles.