Aluminium Chloride

Aluminium chloride, AlCl₃, is the most industrially important aluminium halide.

Preparation. Treating aluminium metal or aluminium hydroxide with hydrochloric acid gives aluminium trichloride, which crystallises as the hydrate on evaporation: 2Al + 6HCl → 2AlCl₃ + 3H₂ and Al(OH)₃ + 3HCl → AlCl₃ + 3H₂O. By the McAfee process, alumina and coke are heated together in a current of chlorine: 2Al₂O₃ + 3C + 6Cl₂ → 4AlCl₃ + 3CO₂. On an industrial scale, aluminium metal is chlorinated directly around 1000 K: 2Al + 3Cl₂ →(1000 K)→ 2AlCl₃.

Properties. Anhydrous aluminium chloride is a colourless, hygroscopic solid. Its aqueous solution is acidic, and it fumes hydrogen chloride in moist air owing to hydrolysis: AlCl₃ + 3H₂O → Al(OH)₃ + 3HCl. With ammonium hydroxide it gives aluminium hydroxide (AlCl₃ + 3NH₄OH → Al(OH)₃ + 3NH₄Cl), and with excess sodium hydroxide it gives sodium aluminate (AlCl₃ + 4NaOH → NaAlO₂ + 2H₂O + 3NaCl). It behaves as a Lewis acid, forming addition compounds with ammonia, phosphine and carbonyl chloride, e.g. AlCl₃.6NH₃. …