Haloform Reaction: Definition , Mechanism, Synthetic Applications, Limitations

Haloform Reaction
Haloform Reaction

 Haloform reaction involves an exhaustive halogenation of a methyl ketone (RCOCH3) in the presence of a base to give a haloform (CHX3).  Where R can be either a hydrogen atom, an alkyl, or an aryl group, and X is a halogen.

Haloform Reaction
Haloform Reaction

The product, after the first step, is more reactive than the starting carbonyl. So the reaction keeps going until all the protons are replaced by the halogen. This makes it challenging to stop the process at monohalogenation.

Acetyl groups can be converted into carboxyl groups in this process. It can also yield cyanide, chloroform (CHCl3), bromoform (CHBr3), or iodoform (CHI3). The reaction of methyl ketones with iodine is the most well-known instance of the haloform reaction.

In this reaction, aldehydes or ketones react with halogens like chlorine, bromine, or iodine in the presence of hydroxide ions to produce haloforms like chloroform (CHCl3), bromoform (CHBr3), or iodoform (CHI3), as well as carboxylic acid. It is also a type of oxidation reaction. This is a unique example of a ketone to carboxylic acid oxidation. This is achievable because the (-)CX3 ion is a suitable leaving group that may be displaced by NaOH.

Mechanism of Haloform Reaction

The reaction mechanism involves the three successive cycles of deprotonation and halogenation at the alpha carbon. After which the base is added to the carbonyl and CX3 is removed as a leaving group. This intermediate product in this case is a trihalogenated ketone. Trihalogenated ketoneis very reactive to a nucleophilic acyl substitution because the leaving group will be well-stabilized by the three halogens

Firstly, in the presence of hydroxide, the halogen disproportionates to produce halide and hypohalite.

The reaction between the hypohalite and the ketone occurs via different steps.

 Step I: The ketone passes via keto-enol tautomerization under basic conditions which is followed by the electrophilic attack of hypohalite on enolate.

Step II: When the α(alpha) position has been exhaustively halogenated, the molecule undergoes a nucleophilic acyl substitution by hydroxide, with −CX3 being the leaving group stabilized by three electron-withdrawing groups. In the third step the −CX3 anion abstracts a proton from either the solvent or the carboxylic acid formed in the previous step, and forms the haloform. At least in some cases (chloral hydrate) the reaction may stop and the intermediate product isolated if conditions are acidic and hypohalite is used.


If the other substituent on the carbonyl groups carries no enolizable -protons, the process can be used synthetically to demethylate methyl ketones.


Acetamide and acetyl chloride are ineffective for this test. The halogen should be sodium hypochlorite, bromine, iodine, or chlorine. This process is ineffective for producing fluoroform (CHF3) since it needs the presence of the incredibly unstable hypofluorite ion. However, when exposed to a base, ketones having the structural formula RCOCF3 cleave, producing fluoroform.


  1. Skyes, P., A Guide Book to Mechanism in Organic Chemistry, Second edition, Orient Longman Ltd., 1988.
  2. March, J., Advanced Organic Chemistry, Wiley Eastern Limited, 1986.
  3. Morrison, R. T., & Boyd, R. N., Organic chemistry, Allyn and Bacon, Inc. 1987

About Author

Photo of author

Kabita Sharma

Kabita Sharma is a graduate student from the central department of chemistry, Tribhuvan University. She has been actively involved in research related to natural products, computational chemistry, and nanochemistry. She is currently working on enzyme assay, molecular docking, and molecular dynamic simulation.

Leave a Comment