Aluminum Halides and Aluminum Nitrate
Authors: Grams G. W. 
Published: August 2004

The aluminum halides and aluminum nitrates have similar properties with the exception of the family of aluminum fluoride compounds which are discussed elsewhere. Of the remaining members in this aluminum halide family, chloride derivatives are the most commercially important. The chemistry of aluminum chloride is influenced significantly by hydration. Aluminum chloride hexahydrate, AlCl3 · 6H2O, is a crystalline solid that dissolves easily in water, forming ionic species. Anhydrous aluminum chloride reacts violently with water, evolving heat, a gas consisting of hydrogen chloride and steam, and aluminum oxide particulates. The uses of anhydrous aluminum chloride and the hydrated form are also very different. The anhydrous material is a Lewis acid used as an alkylation catalyst. The hydrate is used principally as a flocculating aid. Commercially, aluminum chloride is available as the anhydrous AlCl3, as the hexahydrate, AlCl3 · 6H2O, or as a 28% aqueous solution designated 32°Be′. Anhydrous aluminum chloride is a hygroscopic, white solid that reacts with moisture in air. In the United States anhydrous aluminum chloride is manufactured by the exothermic reaction of chlorine, Cl2, vapor with molten aluminum. In storage, over time a pressure build‐up from HCl in the container can occur. Containers should be carefully vented before being opened. Safety goggles or face shields, rubber gloves, rubber shoes, and coveralls made of acid‐resistant material should be used in handling. Aluminum chloride reacts with moisture in the skin, in the eyes, ears, nose, and throat. Fumes resulting from exposure of anhydrous aluminum chloride to moisture are corrosive and acidic. Collection systems should be provided to conduct aluminum chloride dusts or gases to a scrubbing device. The hexahydrate of aluminum chloride is a deliquescent, crystalline solid soluble in water and alcohol and usually made by dissolving aluminum hydroxide, Al(OH)3, in concentrated hydrochloric acid. Roofing granules and mineral aggregate for bituminous products are treated with aluminum chloride solution to improve adhesion of the asphalt. Aluminum chloride hydrate is used in textile finishing to impart crease recovery and nonyellowing properties to cotton fabrics and antistatic characteristics to polyester, polyamide, and acrylic fabrics. The class of compounds identified as basic aluminum chlorides is used primarily in deoderant, antiperspirant, and fungicidal preparations. Anhydrous aluminum bromide, AlBr3, forms colorless trigonal crystals and exists in dimeric form, Al2Br6, in the crystal and liquid phases. Although its catalytic activity is moderate, it can be used in Friedel‐Crafts reactions where selectivity is important. Anhydrous aluminum bromide, prepared from bromine and metallic aluminum, decomposes upon heating. Caution should be exercised in handling this hazardous compound because of its reactivity with water. Aluminum bromide may cause tissue burns, and both the anhydrous and the hydrate forms may be toxic upon ingestion. Aluminum iodide, AlI3, is a crystalline solid with a melting point of 191°C. Aluminum iodide hexahydrate, AlI3 · 6H2O, and aluminum iodide pentadecahydrate, All3 · 15H2O, may be prepared by the reaction of hydroiodic acid, HI, with aluminum or aluminum hydroxide. Aluminum nitrate is available commercially as aluminum nitrate nonahydrate, Al(NO3)3 · 9H2O. It is a white, crystalline material with a melting point of 73.5°C, that is soluble in cold water, alcohols, and acetone. Aluminum nitrate nonahydrate is prepared by dissolving aluminum or aluminum hydroxide in dilute nitric acid. It is made commercially from aluminous materials such as bauxite. Hydrated aluminum nitrate is used in the preparation of insulating papers, on transformer core laminates, and in cathode‐ray tube heating elements.