Aluminum Bromide Formula
Aluminum bromide, also known as aluminum tribromide, is an inorganic salt mostly used as a catalyst in organic synthesis due to its acidic behavior.
Formula and structure: The aluminum bromide chemical formula is AlBr3. The molar mass is 266.69 g/mol. The molecule is formed by one aluminum cation Al3+ and three bromide anions Br-. The molecule is also found as a dimeric structure Al2Br6. The aluminum bromide can also be found as an hexahydrate salt AlBr3.H2O. Its chemical structure can be written as below, in the common representations used for organic molecules.
Occurrence: Aluminum bromide is not found in nature.
Preparation: Aluminum bromide is prepared from the reaction of metallic aluminum or aluminum oxide with hydrobromic acid or through the reaction of metallic aluminum with bromide gas at high temperatures:
2Al + 6HBr → Al2Br6 + 3H2
Al2O3 + 6HBr → Al2Br6 + 3H2O
2Al + 3Br2 → Al2Br6
Physical properties: Aluminum bromide is white to light yellow, pungent powder. The density of this salt is 3.2 g/mol and varies to 2.54 when the salt is hydrated. Its melting point is 97 °C and the boiling point is 255 °C. Aluminum bromide is soluble in water. Although, in water it can suffer hydrolysis. It is soluble in methanol, ethanol and acetone.
Chemical properties: Aluminum bromide is a strong Lewis acid due to the bromine atom has a deficit of electrons that needs to fill out. This is the reason behind the dimerization of AlBr3 to Al2Br6. A Lewis acid is any specie that has a empty orbital in which the specie can accept electrons.
Uses: Aluminum bromide can be used in organic synthesis for catalyzing reactions of alkylation and isomerization. It can also be used as reactant in bromination reactions.
Health effects / safety hazards: Aluminum bromide is highly reactive for being a Lewis acid. It is also extremely harmful for health. It may be flammable.