Chloride Chromium VI Dioxychloride

Submitted by Harry H. Sisler Checked by Louis E. MarchiI 

Among the more common methods used for the preparation of chromyl chloride are the distillation of a mixture of concentrated sulfuric acid with the solid formed by melting 

A solution of 150 g. of chromium(VI) oxide (c.p.) in 100 ml. of water is placed in a 1500-ml. three-necked flask fitted with a dropping funnel, a mechanical stirrer, a thermometer, and a tube to carry away the vapors of chromyl chloride and hydrochloric acid. Three hundred tliirty milliliters of concentrated hydrocliloric acid is added, and the solution is cooled to 0° by an ice-salt mixture. While the solution is stirred, 450 ml. of concentrated sulfuric acid is added drop by drop from the dropping funnel. Ice is added to the cooling bath as needed, and the rate of addition of the sulfuric acid is regulated so that the temperature of the reaction mixture does not rise above 15 to 20°. When all the sulfuric acid has been added, the reaction mixture is transferred to a separatory funnel. After the two liquid layers have separated, the lower layer of chromyl chloride is drawn off into a glass-stoppered container. Yield 189 g. (81 per cent).J 

J When the synthesis was checked, a yield of 90 per cent was obtained. The higher yield is believed to be due to the fact that the temperature was kept below 10°. 

The product is distilled through an 18-in. Vigreux column. The fraction boiling between 115 and 116° at 735 mm. amounts to 65 per cent of the crude product. Since chromyl chloride reacts with stopcock grease and has a tendency to cause glass joints to stick, ground-glass apparatus is not recommended for this distillation. 

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