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, organoch ...
. 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 effecting al ...
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
Allyl chloride is the organic compound with the formula C H2=CHCH2 Cl. This colorless liquid is insoluble in water but soluble in common organic solvents. It is mainly converted to epichlorohydrin, used in the production of plastics. It is a ch ...
, and these considerations guide its use.
Preparation
Allyl bromide is produced commercially from
allyl alcohol
Allyl alcohol ( IUPAC name: prop-2-en-1-ol) is an organic compound with the structural formula . Like many alcohols, it is a water-soluble, colourless liquid. It is more toxic than typical small alcohols. Allyl alcohol is used as a raw material ...
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. H ...
:
:CH
2=CHCH
2OH + HBr → CH
2=CHCH
2Br + H
2O
It can also be prepared by the halogen-exchange reaction between
allyl chloride
Allyl chloride is the organic compound with the formula C H2=CHCH2 Cl. This colorless liquid is insoluble in water but soluble in common organic solvents. It is mainly converted to epichlorohydrin, used in the production of plastics. It is a ch ...
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 petrole ...
.
Reactions and uses
Electrophilic properties
Allyl bromide is an electrophilic alkylating agent.
It reacts with
nucleophiles
In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...
, such as
amines
In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent such ...
,
carbanions
In organic chemistry, a carbanion is an anion in which carbon is trivalent (forms three bonds) and bears a formal negative charge (in at least one significant resonance form).
Formally, a carbanion is the conjugate base of a carbon acid:
:R3C ...
,
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:
: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
Secobarbital (as the sodium salt, originally marketed by Eli Lilly and Company for the treatment of insomnia, and subsequently by other companies as described below, under the brand name Seconal) is a short-acting barbiturate derivative drug that ...
and
thiamylal
Thiamylal (Surital) is a barbiturate derivative invented in the 1950s. It has sedative, anticonvulsant, and hypnotic effects, and is used as a strong but short acting sedative. Thiamylal is still in current use, primarily for induction in surgica ...
.
Preparation of Grignard reagent
Allyl bromide reacts with
magnesium metal in
dry ether to form
allylmagnesium bromide
Allylmagnesium bromide is a Grignard reagent used for introducing the allyl group. It is commonly available as a solution in diethyl ether. It may be synthesized by treatment of magnesium with allyl bromide
Allyl bromide (3-bromopropene) is an or ...
, a Grignard reagent:
:CH
2=CHCH
2Br + Mg → CH
2=CHCH
2MgBr
References
External links
Entry at chemicalland21.com
Organobromides
Allyl compounds
{{organohalide-stub