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Haloform Reaction

March 4, 2013

The Haloform Reaction is a type of organic reaction where haloform is produced by halogenation of methyl ketone in the presence of a base. It is a kind of nuclophilic substitution reaction. This reaction is used in quaitatve analysis to indicate the presence of methyl ketone.

 

Haloform reaction

The halogenation reaction proceeds because the halogen stablises the enolate negative charge and makes it easier to form.  This reaction is usually performed using iodine and as a chemical test for identifying methyl ketones. Iodoform is yellow and precipitates under the reaction conditions.

Mechanism of the reaction

  • The hydroxide ion acts as a base and removes the α-hydrogen producing enolate.
  • The enolate reacts with iodine to form halogenated ketone.
  • The hydroxide now reacts as a nucleophile at the electrophilic carbonyl carbon, with the C=O becoming a C-O single bond and the oxygen is now anionic.
  • The trihalo methyl system is stabilized by three halogens.
  • The trihalo anion abstracts a proton from either from carboxylic acid or solvent forming haloform.

Haloform reaction mechanism

 

Examples

Predict the mechanism for the following haloform reaction

Haloform reaction example

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