Cupric chloride, CuCl₂

The anhydrous Cupric chloride, CuCl₂, is produced by heating copper or cuprous chloride in chlorine, or by dehydrating the dihydrate by heating at 150° C. in an atmosphere of hydrogen chloride, or by addition of concentrated sulphuric acid to its aqueous solution. It is a brownish-yellow, hygroscopic solid, melting at 498° C., of density 3.054. It is readily soluble in water and organic solvents. Its heat of formation from its elements, calculated from the interaction of cupric oxide and hydrochloric acid, is given as 51.63 Cal. And 51.4 Cal. It is decomposed by heat into the cuprous salt and chlorine.

The dihydrate, CuCl₂,2H₂O, is prepared by evaporating a solution of cupric oxide or carbonate in hydrochloric acid; or by evaporating a solution of cupric sulphate and sodium chloride, the dihydrate crystallizing out after sodium sulphate and chloride; or by addition of barium chloride to a solution of cupric sulphate, filtering, and concentrating. It crystallizes in green, deliquescent, rhombic prisms, but a blue, nondeliquescent form has also been described. The density of the dihydrate is 2.47 to 2.535. Its solubility at 17° C. is 43.06 grams in 100 grams of water. A trihydrate, CuCl₂,3H₂O, exists at low temperatures.

Numerous basic cupric chlorides have been described, although some of them may not be true chemical compounds. As examples of these substances may be cited the green, rhombic crystals of the mineral atacamite, CuCl₂,3Cu(OH)₂,wH₂O, containing a varying proportion of water; the crystalline compound CuCl₂,3Cu(OH)₂, formed from brown cupric hydroxide and cupric-chloride solution; and the compound CuCl₂,3CuO,2H₂O, formed by the interaction of solutions of potassium hydroxide and cupric chloride.

Among the double salts of cupric chloride with other metallic salts may be mentioned CuCl₂,LiCl,2H₂O, a red compound; other examples are CuCl₂,2KCl,2H₂O; CuCl₂,KCl₂; and CuCl₂,2NiI₄Cl,2H₂O. References to the literature of other double salts are appended.

In alcoholic solution cupric chloride combines with nitric oxide to form a double compound of the formula CuCl₂,NO.