Reactions
Al2Br6 dissociates readily to give the strong Lewis acid, AlBr3. Regarding the tendency of Al2Br6 to dimerize, it is common for heavier main group halides to exist as aggregates larger than implied by their empirical formulae. Lighter main group halides such as boron tribromide do not show this tendency, in part due to the smaller size of the central atom.
Consistent with its Lewis acidic character, water hydrolizes Al2Br6 with evolution of HBr and formation of Al-OH-Br species. Similarly, it also reacts quickly with alcohols and carboxylic acids, although less vigorously than with water. With simple Lewis bases (L), Al2Br6 forms adducts, such as AlBr3L.
Aluminium tribromide reacts with carbon tetrachloride at 100 °C to form carbon tetrabromide:
- 4 AlBr3 + 3 CCl4 → 4 AlCl3 + 3 CBr4
and with phosgene yields carbonyl bromide and aluminium chlorobromide:
- AlBr3 + COCl2 → COBr2 + AlCl2Br
Al2Br6 is an excellent reagent for Friedel-Crafts and related Lewis acid-promoted reactions such as epoxide ring openings and decomplexation of dienes from iron carbonyls. It is a stronger Lewis acid than the more common Al2Cl6. Because it is hygroscopic, older samples tend to be hydrated and less useful. Impure samples can be purified by vacuum sublimation.
Read more about this topic: Aluminium Bromide
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