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Aurous cyanide, AuCN

The cyanide is produced by the interaction of hydrogen cyanide and auric hydroxide; by double decomposition from auric chloride and mercuric cyanide, with simultaneous production of complex derivatives; and by the decomposition of auric cyanide, as well as by the action of hydrochloric acid on its complex salts at 50° C.:

NaAu(CN)2+HCl=AuCN+NaCl+HCN.

Aurous cyanide forms yellow, microscopic laminae, very slightly soluble in water. It is more stable than aurous iodide, but at red heat is decomposed into gold and cyanogen. Its insolubility renders it immune to the action of dilute acids and hydrogen sulphide, but solutions of ammonia, potassium hydroxide, ammonium sulphide, and sodium thiosulphate dissolve it, probably forming complex derivatives. In aurous cyanide the tendency to form complex compounds is much more marked than in the corresponding chloride, bromide, and iodide. Its interaction with potassium ferrocyanide has been studied by Beutel.

A solution of potassium cyanide dissolves aurous cyanide, and also finely divided gold in presence of air, forming potassium aurocyanide, KAu(CN)2, a substance also produced by anodic solution of gold in a solution of potassium cyanide. The anhydrous salt crystallizes from water in colourless, rhombic octahedra. At ordinary temperatures its solubility is 11.66 grams in 100 grams of water. Its solution absorbs chlorine, bromine, and iodine, forming complex halogen derivatives, containing ions of the type .

Double decomposition of ammonium sulphate and potassium aurocyanide yields ammonium aurocyanide, NH4Au(CN)2. This substance begins to decompose at 100° C. into aurous cyanide, hydrogen cyanide, and ammonia. Sodium aurocyanide, NaAu(CN)2, resembles the corresponding potassium salt in both preparation and properties. Salts of the aurocyanic radical, Au(CN)2', with other metals are also known. The compound HAu(CN)2 has not been isolated, since it decomposes readily with production of hydrogen cyanide.

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