Dehydrohalogenation

Dehydrohalogenation in organic chemistry an elimination reaction - often a β - elimination reaction or β -elimination - or intramolokulare substitution reaction. With elimination of one each of hydrogen and a halogen atom in the same compound is formed is an alkene ( at the 1,2-position by hydrogen and halogen atom), a cyclopropane derivative ( in the 1,3-position by hydrogen and halogen atom), or a heterocyclic compound. The dehydrohalogenation may be used as dehydrofluorination ( elimination of hydrogen fluoride), dehydrochlorination ( elimination of hydrogen chloride), dehydrobromination ( elimination of hydrogen bromide ), etc. are carried out and passes through the action of bases in the appropriate haloalkanes from. Suitable bases used are alkali metal hydroxide solutions, amines, alkylamides and heterocyclic nitrogen compounds such as 1,5-diazabicyclo [ 4.3.0] non -5-ene.

From 1,2 - or 1,1- dihalo- compounds can be synthesized halogen vinyl compounds under the action of alcoholic potash.

Other examples of dehydrohalogenations under the action of a base:

• Formation of oxiranes from β - haloalkanols
• Formation of oxetanes from γ - haloalkanols
• Formation of aziridines from β -halo amines
• Formation of azetidines from γ - haloamines
• Formation of thiiranes from β - Halogenthioalkanolen
• Formation of ketenes from carboxylic acid halides with a hydrogen atom on the α - carbon atom

The formation of the highly reactive and unstable benzyne ( a Arin ) of chlorobenzene is also a dehydrochlorination.

Reaction mechanism

A distinction is made ( E1) and the bimolecular elimination (E2 ) between the monomolecular elimination. There is also the carbanion or E1cB mechanism by which such β -elimination can take place.