Are you an EPFL student looking for a semester project?
Work with us on data science and visualisation projects, and deploy your project as an app on top of GraphSearch.
Concept
Haloform reaction
Summary
In chemistry, the haloform reaction is a chemical reaction in which a haloform (, where X is a halogen) is produced by the exhaustive halogenation of an acetyl group (, where R can be either a hydrogen atom, an alkyl or an aryl group), in the presence of a base. The reaction can be used to transform acetyl groups into carboxyl groups () or to produce chloroform (), bromoform (), or iodoform (). Note that fluoroform () can't be prepared in this way.
In the first step, the halogen dis-proportionates in the presence of hydroxide to give the halide and hypohalite.
Br2 + 2 OH- -> Br- + BrO- + H2O
If a secondary alcohol is present, it is oxidized to a ketone by the hypohalite:
If a methyl ketone is present, it reacts with the hypohalite in a three-step process:
- Under basic conditions, the ketone undergoes keto-enol tautomerisation. The enolate undergoes electrophilic attack by the hypohalite (containing a halogen with a formal +1 charge).
- When the α(alpha) position has been exhaustively halogenated, the molecule undergoes a nucleophilic acyl substitution by hydroxide, with being the leaving group stabilized by three electron-withdrawing groups. In the third step the 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. Substrates are broadly limited to methyl ketones and secondary alcohols oxidizable to methyl ketones, such as isopropanol. The only primary alcohol and aldehyde to undergo this reaction are ethanol and acetaldehyde, respectively. 1,3-Diketones such as acetylacetone also undergo this reaction. β-ketoacids such as acetoacetic acid will also give the test upon heating. Acetyl chloride and acetamide do not undergo this reaction. The halogen used may be chlorine, bromine, iodine or sodium hypochlorite. Fluoroform (CHF3) cannot be prepared by this method as it would require the presence of the highly unstable hypofluorite ion.
Official source
About this result
This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.