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In chemistry, the haloform reaction (also referred to as the Lieben haloform reaction) is a chemical reaction in which a haloform (CHX 3, where X is a halogen) is produced by the exhaustive halogenation of an acetyl group (R−C(=O)CH 3, where R can be either a hydrogen atom, an alkyl or an aryl group), in the presence of a base.
In chemistry, halogenation is a chemical reaction which introduces one or more halogens into a chemical compound. Halide-containing compounds are pervasive, making this type of transformation important, e.g. in the production of polymers, drugs. [1] This kind of conversion is in fact so common that a comprehensive overview is challenging.
For example, phenols and anilines react quickly with chlorine and bromine water to give multihalogenated products. Many detailed laboratory procedures are available. [ 5 ] For alkylbenzene derivatives, e.g. toluene , the alkyl positions tend to be halogenated by free radical conditions, whereas ring halogenation is favored in the presence of ...
For example, consider radical bromination of toluene: [5] bromination of toluene with hydrobromic acid and hydrogen peroxide in water. This reaction takes place on water instead of an organic solvent and the bromine is obtained from oxidation of hydrobromic acid with hydrogen peroxide. An incandescent light bulb suffices to radicalize.
In organic chemistry, an electrophilic aromatic halogenation is a type of electrophilic aromatic substitution. This organic reaction is typical of aromatic compounds and a very useful method for adding substituents to an aromatic system.
The most widely practised example of this reaction is the ethylation of benzene. Approximately 24,700,000 tons were produced in 1999. [2] (After dehydrogenation and polymerization, the commodity plastic polystyrene is produced.) In this process, acids are used as catalyst to generate the incipient carbocation. Many other electrophilic reactions ...
Regiochemistry follows from the reaction mechanism, which exhibits halogen attack on the least-hindered unsaturated carbon. The mechanism for this chain reaction resembles free radical halogenation, in which the peroxide promotes formation of the bromine radical. However, this process is restricted to addition of HBr.
A classic example for favoring the keto form can be seen in the equilibrium between vinyl alcohol and acetaldehyde (K = [enol]/[keto] ≈ 3 × 10 −7). In 1,3-diketones, such as acetylacetone (2,4-pentanedione), the enol form is favored. The acid-catalyzed conversion of an enol to the keto form proceeds by proton transfer from O to carbon.