Allyl bromide

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Allyl bromide

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UN number	1099
Template:Longitem	Template:Chembox Elements/molecular formula
Molar mass	Template:Chem molar mass
Appearance	Clear to light yellow liquid
Odor	Unpleasant, irritating, pungent
Density	1.398 g/cm3
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log P	1.79
Vapor pressure	18.6 kPa
Template:Longitem	−58.6·10−6 cm3·mol−1
Template:Longitem	1.4697 (20 °C, 589.2 nm)
Viscosity	0.471 cP
Template:Longitem	≈1.9 D
Template:Longitem	12.2 kJ·mol−1 (liquid) 45.2 kJ·mol−1 (gas)
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Explosive limits	4.3–7.3 %
Template:Longitem	Allyl chloride Allyl iodide

Allyl bromide (3-bromopropene) is an organic halide. It is an alkylating agent used in synthesis of polymers, pharmaceuticals, perfumes and other organic compounds. Allyl bromide is a colorless liquid, although commercial samples appear yellow or brown. It is an irritant and a potentially dangerous alkylating agent. Allyl bromide is more reactive but more expensive than allyl chloride, and these considerations guide its use.

Preparation

Hydrohalogenation

Allyl bromide is produced commercially from allyl alcohol and hydrobromic acid:

CH₂=CHCH₂OH + HBr → CH₂=CHCH₂Br + H₂O

It can also be prepared by the halogen-exchange reaction between allyl chloride and hydrobromic acid or by the allylic bromination of propene.

Reactions and uses

Allyl bromide is an electrophilic alkylating agent. It reacts with nucleophiles, such as amines, carbanions, alkoxides, etc., to introduce the allyl group:

CH₂=CHCH₂Br + Nu⁻ → CH₂=CHCH₂Nu + Br⁻ (Nu⁻ is a nucleophile)

It is used in the synthesis of compounds containing the allyl functionality, such as the pharmaceuticals methohexital, secobarbital and thiamylal.

Allyl bromide reacts with magnesium metal in dry ether to form allylmagnesium bromide, a Grignard reagent:

CH₂=CHCH₂Br + Mg → CH₂=CHCH₂MgBr

External links

• Entry at chemicalland21.com