Halogenation

Halogenation is a chemical reaction that replaces a hydrogen atom with a halogen atom. More specific descriptions exist that specify the type of halogen: fluorination, chlorination, bromination, and iodination.

In a Markovnikov addition reaction, a halogen like bromine is reacted with an alkene which causes the π-bond to break forming an haloalkane. This makes the hydrocarbon more reactive and bromine as it turns out, is a good leaving group in further chemical reactions such as nucleophilic aliphatic substitution reactions and elimination reactions

Several types of halogenation exist, including:

• Free radical halogenation
• Ketone halogenation
• Electrophilic halogenation
• Halogen addition reaction

An example of halogenation can be found in the organic synthesis of the anesthetic halothane from trichloroethylene which involves a high temperature bromination in the second step :

Halothane synthesis

Halogenation of Hydrocarbons

It has been shown that the reaction of bromine water, for instance, in ethene caused the formation of 2-bromoethanol. This formation of alcohol which has the same trends for other aliphatic hydrocarbons yielded the colorless mixture formed. The case was different in benzene and cyclohexane. When bromine water reacted with toluene it yielded a bromophenol which caused the faint yellow color of the upper layer.

See also

• Haloalkane (Alkyl halide)
• Halogenoarene (Aryl halide)
• Haloketone
• Electrophilic substitution