Boron tribromide

Boron tribromide

Names
IUPAC name Boron tribromide
Other names Tribromoborane, Boron bromide
Identifiers
CAS Number	10294-33-4 Y
ChemSpider	16787736 Y
EC Number	233-657-9
Jmol 3D model	Interactive image Interactive image
PubChem	25134
RTECS number	ED7400000
UN number	2692
InChI InChI=1S/B.3BrH/h;3*1H/q+3;;;/p-3 Y Key: LKBREHQHCVRNFR-UHFFFAOYSA-K Y InChI=1/BBr3/c2-1(3)4 Key: ILAHWRKJUDSMFH-UHFFFAOYAA InChI=1/B.3BrH/h;3*1H/q+3;;;/p-3 Key: LKBREHQHCVRNFR-DFZHHIFOAX
SMILES BrB(Br)Br [BH6+3].[Br-].[Br-].[Br-]
Properties
Chemical formula	BBr3
Molar mass	250.52 g/mol
Appearance	colorless to amber liquid
Odor	sharp and irritating
Density	2.643 g/cm3
Melting point	−46.3 °C (−51.3 °F; 226.8 K)
Boiling point	91.3 °C (196.3 °F; 364.4 K)
Solubility in water	reacts violently
Solubility	soluble in ethanol, CCl4
Vapor pressure	7.2 kPa (20 °C)
Refractive index (nD)	1.00207
Viscosity	7.31 x 10−4 Pa s (20 °C)
Thermochemistry
Specific heat capacity (C)	0.2706 J/K
Std molar entropy (So298)	228 J/mol K
Std enthalpy of formation (ΔfHo298)	-0.8207 kJ/g
Vapor pressure	{{{value}}}
Related compounds
Related compounds	Boron trifluoride Boron trichloride Boron triiodide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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

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 to give a hydroxyl group, boric acid, and hydrogen bromide as products.

ROBBr₂ + 3H₂O → ROH + B(OH)₃ + 2HBr

It also finds applications in olefin polymerization and in Friedel-Crafts chemistry as a Lewis acid catalyst.

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

Synthesis

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

History

The first synthesis was done by M. 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

Pharmaceutical Manufacturing
Image Processing
Semiconductor Doping
Semiconductor Plasma Etching
Photovoltaic Manufacturing
Reagent for Various Chemical Processes

See also

• List of highly toxic gases

External links

• Boron Tribromide at The Periodic Table of Videos (University of Nottingham)
• NIOSH Pocket Guide to Chemical Hazards - Boron Tribromide (Centers for Disease Control and Prevention)
• US patent 2989375, May, F. H.; Bradford, J. L., "Production of Boron Tribromide", issued 1961-06-20, assigned to American Potash & Chemical