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Synthesis of Aluminum Chloride


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Anhydrous Aluminum Chloride [1,2]

One end of a large diameter Vycor tube (25 to 40 mm) is inserted through one of two holes in a cork closing a wide-neck flask. The second hole holds a tube leading to the hood. The cork can dispensed with if the reaction tube can be made to fit tightly into the neck of a long-neck, round bottom flask. The reaction tube is placed in an electric furnace. The distance between the hot zone and the receiver flask should not be longer than 8 cm, to prevent plugging of the tube by the sublimate. The cork is protected from the heat by an asbestos wrapping. A porcelain boat containing aluminum turnings or powder is inserted into the reaction tube. Gaseous HCl is then passed through the end opposite the receiver. The rubber tubing connections should be as short as possible. When the air has been completely displaced by the HCl, the furnace is slowly heated until a white mist begins to appear. The flow of HCl is then increased and the temperature raised to prevent premature condensation of the sublimate. The reaction is then allowed to continue until the aluminum has been completely consumed.

Aluminum Chloride Hexahydrate

At 0C, aluminum chloride hydrate is slightly soluble (21mg/100ml) in saturated aqueous HCl and is therefore easily isolated from such a solution. The aluminum is dissolved in concentrated HCl and the solution is transferred into a three neck flask fitted with a stirrer, an inlet tube for HCl gas and an outlet tube. The flask is cooled to 0C and HCl is introduced into the continuously stirred and cooled solution until it is saturated. The inlet tube should not dip into the solution, since it might become clogged with salt, but sufficient adsorption of the HCl is ensured by vigorous stirring. A wash bottle filled with concentrated sulfuric acid connected to the outlet of the flask serves to indicate the progress of the saturation. The precipitated hydrate is rapidly suction filtered and, while cold, washed with some ether and dried on a clay plate.

Anhydrous Aluminium Bromide [3]

Put 6 g Al turnings in a 250 ml two-neck flask. Add dropwise from a sep funnel 13 ml Br2 at such a rate as to maintain a steady reaction. When the addition is complete distil the product directly into a receiving flask, the outlet of which is guarded with a phosphorous pentoxide drying tube. A second distillation over Al turnings may be necessary to obtain a colourless solid, mp 97.5C, bp 255C.

Note: Carry out in fume cupboard. Compound reacts violently with water. Surplus material may be disposed off by reaction with alcohol.

References

[1] Ber. 25, 3521 (1892)
[2] J. Chem. Soc. 1914 (1952)
[3] Advanced Practical Inorganic Chemistry, D.M. Adams & J.B. Raynor