The base catalysed prototropy of substituted acetones

Abstract

Kinetic measurements have been made at 25° on the catalysed halogenation of the following ketones: acetone, acetonylacetone, monochloroacetone, monobromoacetone, as . dichloroacetone and acetylacetone. In all cases the reactions are of zero order with respect to the halogen and exhibit general basic catalysis. For the first two ketones general acid catalysis is also detectable. For each ketone the catalytic constants k B of four carboxylate anions are related to the dissociation constants K A of the corresponding acids by an equation of the type k B = G (1/ K A ) α , where G and the α are constants for a given ketone. The catalytic constants measured cover a range of about 10 8 . Examination of the results (together with those of Pedersen for the bromination of acetoacetic ester and acetoacetic acid) shows that the exponent α decreases steadily from 0.88 to 0.48 as the reactivity of the ketone increases. The catalytic coefficients of the water molecule are given approximately by the equations valid for the carboxylate anions, but the hydroxyl ion is in each case much less effective as a catalyst than these equations predict.