Boron tribromide

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Boron tribromide
Boron tribromide
Identifiers
CAS number 10294-33-4 YesY
PubChem 25134
ChemSpider 16787736 YesY
EC number 233-657-9
UN number 2692
RTECS number ED7400000
Jmol-3D images Image 1
Image 2
Properties
Molecular formula BBr3
Molar mass 250.52 g/mol
Appearance colorless to amber liquid
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
Hazards[1]
MSDS ICSC 0230
GHS pictograms Acute Tox. 2Skin Corr. 1B
GHS signal word DANGER
GHS hazard statements H330, H300, H314 Within the European Union, the following additional hazard statement (EUH014) must also be displayed on labelling: Reacts violently with water.
EU Index 005-003-00-0
EU classification Very toxic (T+)
Corrosive (C)
R-phrases R14, R26/28, R35
S-phrases (S1/2), S9, S26, S28, S36/37/39, S45
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorus Special hazard W: Reacts with water in an unusual or dangerous manner. E.g., cesium, sodiumNFPA 704 four-colored diamond
Flash point −18 °C (0 °F; 255 K)
Related compounds
Related compounds Boron trifluoride
Boron trichloride
Boron triiodide
Except where noted otherwise, 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.[2]

Chemical properties[edit]

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.

Synthesis[edit]

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[edit]

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[edit]

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

See also[edit]

References[edit]

  1. ^ Index no. 005-003-00-0 of Annex VI, Part 3, to Regulation (EC) No 1272/2008 of the European Parliament and of the Council of 16 December 2008 on classification, labelling and packaging of substances and mixtures, amending and repealing Directives 67/548/EEC and 1999/45/EC, and amending Regulation (EC) No 1907/2006. OJEU L353, 31.12.2008, pp 1–1355 at p 341.
  2. ^ "Boron Tribromide". Toxicologic Review of Selected Chemicals. National Institute for Occupational Safety and Health. 
  3. ^ Doyagüez, E. G. (2005). "Boron Tribromide" (pdf). Synlett 2005 (10): 1636–1637. doi:10.1055/s-2005-868513. 
  4. ^ Sousa, C. & Silva, P.J (2013). "BBr3-Assisted Cleavage of Most Ethers Does Not Follow the Commonly Assumed Mechanism" (pdf). Eur. J. Org. CHem n/a (n/a): n/a. doi:10.1002/ejoc.201300337. 
  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. 

Further reading[edit]

External links[edit]