Alkylation of Enolates

The mechanism happens like this:

• An acid-base reaction pulls a hydrogen off of the methyl side group (the alpha carbon group), leaving behind an enolate.

• The halogen attaches to the enolate.

• The reaction is repeated twice more with the eventual production of a trihalogenated ketone.

• The hydroxide ion attacks the tri-halogenated molecule, replacing it to make an oxygen anion and a trihalomethane molecule (that gets protonated for stability).

The tri-halogen molecule will be so electronegative that it pulls the remaining hydrogen off of the carboxylic acid to make a carboxylate.

ALKYLATION OF ENOLATES

Enolates can undergo a nucleophilic substitution reaction in which the alpha hydrogen gets pulled off in the presence of a base and an alkyl halide. This alkyl group replaces the alpha hydrogen in the ketone molecule. The reaction works best with methyl halides.

This reaction starts with an acid-base reaction that pulls off the alpha hydrogen, leaving behind the enolate. Then the nucleophilic enolate attacks the alkyl halide, pulling off the alkyl group and leaving behind the halide anion. This is seen in figure 85:

Figure 85.