Ketones methyl, cleavage with halogens

Lieben iodoform reaction. Cleavage of methyl ketones with halogens (mostly iodine) and base to carboxylic acids and haloform. 

Unlike its acid-catalyzed counterpart, a halogenation in base cannot normally be limited to monosubstitution, and this limits its synthetic applications. Methyl ketones, however, undergo a novel C—C cleavage on treatment with halogens in aqueous base. 

Unlike Its acid catalyzed counterpart a halogenation m base cannot normally be limited to monohalogenation Methyl ketones for example undergo a novel polyhalo genation and cleavage on treatment with a halogen m aqueous base... 

Methyl ketones are degraded to the next lower carboxylic acid by reaction with hypochlorite or hypobromite ions. The initial step in these reactions involves base-catalyzed halogenation. The a-haloketones are more reactive than their precursors, and rapid halogenation to the trihalo compound results. Trihalomethyl ketones are susceptible to alkaline cleavage because of the inductive stabilization provided by the halogen atoms. 

The result is that, if the monobromoketone is desired, the reaction is carried out best with an acidic catalyst rather than a basic catalyst. A further complication in the base-catalyzed halogenation of a methyl ketone is that the trihalo-ketone formed is attacked readily by base, thereby resulting in cleavage of a carbon-carbon bond ... 

The cleavage reaction does not occur unless there are three halogens on the carbon, so only methyl groups are removed in this manner. The reaction with 12 (iodoform reaction) has been used as a test for methyl ketones. The formation of iodoform (CHI3),... 

Halogenation of a methyl ketone with excess halogen, called the haloform reaction, results in cleavage of a carbon-carbon o bond and formation of two products, a carboxylate anion and CHX3 (commonly called haloform). 

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