Boron tribromide, BBr₃, is a colorless, fuming liquid compound containing boron and

bromine Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table ( halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simi ...

. Commercial samples usually are amber to red/brown, due to weak bromine contamination. It is decomposed by water and alcohols.

Chemical properties

Boron tribromide is commercially available and is a strong Lewis acid. It is an excellent demethylating or dealkylating agent for the cleavage of

ether In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula , where R and R′ represent the alkyl or aryl groups. Ethers can again be ...

s, also with subsequent cyclization, often in the production of pharmaceuticals. The mechanism of dealkylation of tertiary alkyl ethers proceeds via the formation of a complex between the boron center and the ether oxygen followed by the elimination of an alkyl bromide to yield a dibromo(organo)

borane Trihydridoboron, also known as borane or borine, is an unstable and highly reactive molecule with the chemical formula . The preparation of borane carbonyl, BH3(CO), played an important role in exploring the chemistry of boranes, as it indicated ...

. :ROR + BBr₃ → RO⁺(⁻BBr₃)R → ROBBr₂ + RBr Aryl methyl ethers (as well as activated primary alkyl ethers), on the other hand are dealkylated through a bimolecular mechanism involving two BBr₃-ether adducts. :RO⁺(⁻BBr₃)CH₃ + RO⁺(⁻BBr₃)CH₃→ RO(⁻BBr₃) + CH₃Br + RO⁺(BBr₂)CH₃ The dibromo(organo)borane can then undergo

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolys ...

to give a hydroxyl group,

boric acid Boric acid, more specifically orthoboric acid, is a compound of boron, oxygen, and hydrogen with formula . It may also be called hydrogen borate or boracic acid. It is usually encountered as colorless crystals or a white powder, that dissolve ...

, and

hydrogen bromide Hydrogen bromide is the inorganic compound with the formula . It is a hydrogen halide consisting of hydrogen and bromine. A colorless gas, it dissolves in water, forming hydrobromic acid, which is saturated at 68.85% HBr by weight at room tempe ...

as products. :ROBBr₂ + 3H₂O → ROH + B(OH)₃ + 2HBr It also finds applications in olefin

polymer A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...

ization and in Friedel-Crafts chemistry as a Lewis acid

catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

. The electronics industry uses boron tribromide as a boron source in pre-deposition processes for doping in the manufacture of semiconductors. Boron tribromide also mediates the dealkylation of aryl alkyl ethers, for example

demethylation Demethylation is the chemical process resulting in the removal of a methyl group (CH3) from a molecule. A common way of demethylation is the replacement of a methyl group by a hydrogen atom, resulting in a net loss of one carbon and two hydrogen at ...

of 3,4-dimethoxystyrene into 3,4-dihydroxystyrene.

Synthesis

The reaction of boron carbide with

at temperatures above 300 °C leads to the formation of boron tribromide. The product can be purified by vacuum

distillation Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the heat ...

History

The first synthesis was done by Poggiale in 1846 by reacting boron trioxide with carbon and bromine at high temperatures: :B₂O₃ + 3 C + 3 Br₂ → 2 BBr₃ + 3 CO An improvement of this method was developed by F. Wöhler and Deville in 1857. By starting from amorphous boron the reaction temperatures are lower and no carbon monoxide is produced: :2 B + 3 Br₂ → 2 BBr₃

Applications

Boron tribromide is used in organic synthesis, pharmaceutical manufacturing, image processing, semiconductor doping, semiconductor plasma etching, and photovoltaic manufacturing.

References

External links

Boron Tribromide
at ''

The Periodic Table of Videos ''Periodic Videos'' (also known as ''The Periodic Table of Videos'') is a video project and YouTube channel on chemistry. It consists of a series of videos about chemical elements and the periodic table, with additional videos on other topics i ...

'' (University of Nottingham)
NIOSH Pocket Guide to Chemical Hazards - Boron Tribromide
(Centers for Disease Control and Prevention) * * {{bromine compounds Boron compounds Bromides Boron halides Acid catalysts