Aluminium chloride

Aluminium chloride:

Preparation:

When aluminium metal or aluminium hydroxide is treated with hydrochloric acid, aluminium trichloride is formed. The reaction mixture is evaporated to obtain hydrated aluminium chloride.

2Al + 6HCl → 2AlCl₃ + 3H₂

Al(OH)₃ + 3HCl → AlCl₃ + 3H₂O

McAfee Process:

Aluminium chloride is obtained by heating a mixture of alumina and coke in a current of chlorine.

Al₂O₃ +3C + 3Cl₂  → 2AlCl₃ + 3CO₂

On industrial scale it is prepared by chlorinating aluminium around 1000 K

Properties:

Anhydrous aluminium chloride is a colourless, hygroscopic substance.

An aqueous solution of aluminium chloride is acidic in nature. It also produces hydrogen chloride fumes in moist air.

AlCl₃ + 3H₂O → Al(OH)₃ + 3HCl

With ammonium hydroxide it forms aluminium hydroxide.

AlCl₃ + 3NH₄OH → Al(OH)₃ + 3NH₄Cl

With excess of sodium hydroxide it produces metal aluminate

AlCl₃ + 4NaOH → NaAlO₂ + 2H₂O + 3NaCl

It behaves like a Lewis acid and forms addition compounds with ammonia, phosphine and carbonylchloride etc... Eg. AlCl₃.6NH₃.

Uses of aluminium chloride:

·           Anhydrous aluminium chloride is used as a catalyst in Friedels Crafts reactions

·           It is used for the manufacture of petrol by cracking the mineral oils.

·           It is used as a catalyst in the manufacture on dyes, drugs and perfumes.