Allyl bromide (3-bromopropene) is an
organic halide
Halocarbon compounds are chemicals in which one or more carbon atoms are linked by covalent bonds with one or more halogen atoms (fluorine, chlorine, bromine or iodine – ) resulting in the formation of organofluorine compounds, organochl ...
. It is an
alkylating agent
Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene (or their equivalents). Alkylating agents are reagents for effectin ...
used in synthesis of polymers, pharmaceuticals,
synthetic perfumes and other organic compounds. Physically, allyl bromide is a colorless liquid with an irritating and persistent smell, however, commercial samples are yellow or brown.
Allyl bromide is more reactive but more expensive than
allyl chloride, and these considerations guide its use.
Preparation
Allyl bromide is produced commercially from
allyl alcohol and
hydrobromic acid
Hydrobromic acid is a strong acid formed by dissolving the diatomic molecule hydrogen bromide (HBr) in water. "Constant boiling" hydrobromic acid is an aqueous solution that distills at and contains 47.6% HBr by mass, which is 8.77 mol/L. ...
:
:CH
2=CHCH
2OH + HBr → CH
2=CHCH
2Br + H
2O
It can also be prepared by the halogen-exchange reaction between
allyl chloride and hydrobromic acid or by the
allylic bromination of
propene
Propylene, also known as propene, is an unsaturated organic compound with the chemical formula CH3CH=CH2. It has one double bond, and is the second simplest member of the alkene class of hydrocarbons. It is a colorless gas with a faint petrol ...
.
Reactions and uses
Electrophilic properties
Allyl bromide is an electrophilic alkylating agent.
It reacts with
nucleophiles, such as
amines,
carbanions,
alkoxides
In chemistry, an alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They are written as , where R is the organic substituent. Alkoxides are strong bases and, w ...
, etc., to introduce the
allyl group
In organic chemistry, an allyl group is a substituent with the structural formula , where R is the rest of the molecule. It consists of a methylene bridge () attached to a vinyl group (). The name is derived from the scientific name for garlic, . ...
:
:CH
2=CHCH
2Br + Nu
− → CH
2=CHCH
2Nu + Br
− (Nu
− is a nucleophile)
It is used in the synthesis of compounds containing the allyl functionality, such as the pharmaceuticals
methohexital
Methohexital or methohexitone (marketed under the brand names Brevital and Brietal) is a drug which is a barbiturate derivative. It is classified as short-acting, and has a rapid onset of action. It is similar in its effects to sodium thiopental, ...
,
secobarbital and
thiamylal.
Preparation of Grignard reagent
Allyl bromide reacts with
magnesium metal in
dry ether to form
allylmagnesium bromide, a Grignard reagent:
:CH
2=CHCH
2Br + Mg → CH
2=CHCH
2MgBr
References
External links
Entry at chemicalland21.com
Organobromides
Allyl compounds
{{organohalide-stub