Reactions

The reaction begins with the deprotonation of an α-hydrogen by a base, generating a stabilized enolate anion. This enolate acts as a nucleophile, attacks a molecule of dihalogen and yields a carbonyl compound bearing one halogen substituent at the α-carbon. These two steps, deprotonation and halogenation are repeated until all three α-hydrogen are replaced by halogen atoms. This intermediate then undergoes nucleophilic acyl substitution: the hydroxide ion attacks the electrophilic carbonyl carbon, forming a tetrahedral intermediate, which collapses with the expulsion of the trihalomethyl carbanion as leaving group. This departure is facilitated by the strong electron-withdrawing effect of the three halogen atoms, which stabilize the negative charge. This latter immediately deprotonates the acid and the carboxylate is acidified upon workup to regenerate the carboxylic acid.

This reaction is often used to determine whether a compound contains a methylketone group or can be oxidized to a methylketone. Upon addition of iodine in a basic medium, the reaction produces iodoform, a characteristic yellow precipitate.