Haloform Reaction
The Lieben Haloform reaction allows the transformation of methyl ketones into carboxylic acids producing haloform.
General features: 1. A way of synthesizing carboxylic acids with one less carbon atom. 2. The reaction is usually conducted in aqueous alkali. 3. The halogen can be chlorine, bromine, and iodine. 4. A side reaction is the α-halogenation and subsequent cleavage of the other alkyl group.
Haloform Reaction
Reaction Mechanism
1. Deprotonation and formation of the enolate ion. 2. Sequential halogenation of the methyl group. 3. Hydrolysis of the trihalomethyl ketone. 4. Formation of the carboxylate (carboxylic acid) and haloform.
Example
Experimental Procedure
To a solution of the methyl ketone (10 mL, 48.52 mmol) in EtOH (110 mL) was added NaClO solution (220 mL, 13%) in portions at 0 ºC. The reaction mixture was stirred at room temperature for 12 h. When the reaction was completed, the mixture was acidified to pH = 1 with concentrated HCl. The reaction mixture was extracted with dichloromethane, washed with water and brine, and dried over MgSO4. The solvent was evaporated under reduced pressure to give the crude product, which was purified through flash column chromatography to afford the desired carboxylic acid (92% yield).
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