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.