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a salt of hydrocyanic acid. The cyanide salts of the alkali metals MCN and the alkaline-earth metals M(CN)2, where M is a metal, are thermally stable but are hydrolyzed in aqueous solutions. The cyanides of the heavy metals are thermally unstable and, with the exception of Hg(CN)2, are insoluble in water.
The oxidation of cyanides leads to the formation of cyanates; for example, 2KCN + O2 → 2KOCN. Many metals upon the action of an excess of potassium cyanide or sodium cyanide yield complexes. This proves useful in the extraction of gold and silver from ores (cyanidation, cyanide process):
4NaCN + 2Au + ½O2 + H2O → 2Na[ Au(CN)2] + 2NaOH
Gold and silver are separated from solution by electrodeposition or by the action of metallic zinc. Solutions of the cyanide complexes of gold, silver, zinc, and other metals are used in electroplating technology for the production of coatings. Cyanides are also used in organic synthesis, for example, in the production of nitriles, and as catalysts (in benzoin condensation).
Cyanides are extremely toxic. (For information on the effect of cyanides on the organism and on safety measures when handling them, seeHYDROCYANIC ACID.)
REFERENCESBobkov, S. S., and S. K. Smirnov. Sinil’naia kislota. Moscow, 1970.
Zil’berman, E. N. Reaktsii nitrilov. Moscow, 1972.
Tomilov, A. P., and S. K. Smirnov. Adipodinitril i geksamet ilendiamin. Moscow, 1974.
Williams, H. E. Cyanogen Compounds, 2nd ed. London, 1948.
Migrdichian, V. The Chemistry of Organic Cyanogen Compounds. New York, 1947.
Methoden der Organischen Chemie (Houben-Weyl), 4th ed., vol. 8. Stuttgart, 1952.
S. K. SMIRNOV