Boron tribromide

Boron tribromide, BBr₃, is a liquid compound containing boron and bromine. It is usually made by heating boron oxide with carbon in the presence of bromine: this generates free boron which reacts vigorously with the bromine. It is very volatile and fumes in air because it reacts vigorously with water to form boric acid and hydrogen bromide.

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This compound is commercially available and acts as a strong Lewis acid. Boron Tribromide is an excellent demethylating or dealkylating agent for ethers, often in the production of pharmaceuticals. Additionally, 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^[1].

As briefly touched upon it is important to note also that this chemical will explode upon contact with water. The severity of this explosion will range from the container holding the boron tribromide shattering and exploding over the lab. Or if the quantity of boron tribromide is sufficient will cause a substansive explosion that will be both hazardous to life and the structual integretity of the lab in question. See Vacwell Engineering Company v BHD Chemicals Ltd [1969] 1 A.C 191.

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 reactin Boron trioxide with carbon and bromine at high temperatures.^[2]

B₂O₃ + 3C + Br₂ → 2 BBr₃ + 3CO

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 non carbon monoxide is produces.^[3]

2B + 3 Br₂ → 2 BBr₃

References

1. ^ http://www.albemarle.com/TDS/Fine_chemistry_services/BC-0196_BORON_Tri-Bromide.pdf
2. ^ M. Poggiale (1846). "Bore - Sur un nouveau composé de brome et de bore, l'acide bromoborique et le bromoborate d'ammoniaque". Comptes rendus hebdomadaires 22: 124-130.
3. ^ F. Wöhler, H. E. S.-C. Deville (1858). "Du bore". Annales de chimie et de physique 52: 63-92.