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==