Boron tribromide

Boron tribromide, BBr3, is a colorless, fuming liquid compound containing boron and bromine. Commercial samples usually are amber to red/brown, due to weak bromine contamination. It is decomposed by water and alcohols.[2]

Boron tribromide
Names
IUPAC name
Boron tribromide
Other names
Tribromoborane, Boron bromide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.030.585
EC Number
  • 233-657-9
RTECS number
  • ED7400000
UNII
UN number 2692
Properties
BBr3
Molar mass 250.52 g·mol−1
Appearance Colorless to amber liquid
Odor Sharp and irritating[1]
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)
Reacts violently with water and other protic solvents
Solubility Soluble in CH2Cl2, CCl4
Vapor pressure 7.2 kPa (20 °C)
1.00207
Viscosity 7.31 x 10−4 Pa s (20 °C)
Thermochemistry
0.2706 J/K
228 J/mol K
-0.8207 kJ/g
Hazards
Main hazards Reacts violently with water, potassium, sodium, and alcohols; attacks metals, wood, and rubber[1]
Safety data sheet ICSC 0230
GHS pictograms
GHS Signal word Danger
H330, H300, H314 Within the European Union, the following additional hazard statement (EUH014) must also be displayed on labeling: Reacts violently with water.
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acid
0
3
2
Flash point Noncombustible[1]
NIOSH (US health exposure limits):
PEL (Permissible)
 None[1]
REL (Recommended)
 C 1 ppm (10 mg/m3)[1]
IDLH (Immediate danger)
 N.D.[1]
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).
N verify (what is YN ?)
Infobox references

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.[3]

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.[4]

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.[5]

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.[6] 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:[7]

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:[8]

2 B + 3 Br2 → 2 BBr3

Applications

Boron tribromide is used in organic synthesis,[9] pharmaceutical manufacturing, image processing, semiconductor doping, semiconductor plasma etching, and photovoltaic manufacturing.

See also

References
  1. NIOSH Pocket Guide to Chemical Hazards. "#0061". National Institute for Occupational Safety and Health (NIOSH).
  2. "Boron Tribromide". Toxicologic Review of Selected Chemicals. National Institute for Occupational Safety and Health. 2018-09-21.
  3. Doyagüez, E. G. (2005). "Boron Tribromide" (PDF). Synlett. 2005 (10): 1636–1637. doi:10.1055/s-2005-868513. Archived from the original (pdf) on 2014-12-07. Retrieved 2012-05-16.
  4. Sousa, C. & Silva, P.J. (2013). "BBr3-Assisted Cleavage of Most Ethers Does Not Follow the Commonly Assumed Mechanism". Eur. J. Org. Chem. 2013 (23): 5195–5199. doi:10.1002/ejoc.201300337. hdl:10284/7826.
  5. McOmie, J. F. W.; Watts, M. L.; West, D. E. (1968). "Demethylation of Aryl Methyl Ethers by Boron Tribromide". Tetrahedron. 24 (5): 2289–2292. doi:10.1016/0040-4020(68)88130-X.
  6. Komatsu, Y.; Mihailetchi, V. D.; Geerligs, L. J.; van Dijk, B.; Rem, J. B.; Harris, M. (2009). "Homogeneous p+ emitter diffused using borontribromide for record 16.4% screen-printed large area n-type mc-Si solar cell". Solar Energy Materials and Solar Cells. 93 (6–7): 750–752. doi:10.1016/j.solmat.2008.09.019.
  7. Poggiale, M. (1846). "Nouveau composé de brome et de bore, ou acide bromoborique et bromoborate d'ammoniaque". Comptes Rendus Hebdomadaires des Séances de l'Académie des Sciences. 22: 124–130.
  8. Wöhler, F.; Deville, H. E. S.-C. (1858). "Du Bore". Annales de Chimie et de Physique. 52: 63–92.
  9. Akira Suzuki, Shoji Hara, Xianhai Huang (2006). Boron Tribromide. E-EROS Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rb244.pub2. ISBN 978-0471936237.CS1 maint: multiple names: authors list (link)

Further reading
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