Sodium cyanide is an inorganic compound with the formula NaCN. This highly toxic colourless salt is used mainly in gold mining but has other niche applications. It is an inorganic salt derived from neutralization reactions involving the weak acid hydrogen cyanide.
Production and chemical properties
Sodium cyanide is produced by treating hydrogen cyanide with sodium hydroxide:
Worldwide production was estimated at 500,000 tons in the year 2006. In former times, it was prepared by the Castner-Kellner process involving the reaction of sodium amide with carbon at elevated temperatures.
The structure of solid NaCN is related to that of sodium chloride. The anions and cations are each six-coordinate (KCN has a similar structure). Each Na+ forms pi-bonds to two CN- groups as well as two "bent" K---CN and two "bent "K---NC links.
Because the salt is derived from a weak acid, NaCN readily reverts back to HCN by hydrolysis: the moist solid emits small amounts of hydrogen cyanide, which smells like bitter almonds (not everyone can smell it—the ability thereof is due to a genetic trait). Sodium cyanide reacts rapidly with strong acids to release hydrogen cyanide. This dangerous process represents a significant risk associated with cyanide salts. It is detoxified most efficiently with hydrogen peroxide:
Sodium cyanide is mainly used to extract gold and other precious metals in mining. This application exploits the high affinity of gold(I) for cyanide, which induces gold metal to oxidize and dissolve in the presence of air and water.
Few alternative methods exist for this extraction process.
Several commercially significant chemical compounds are derived from cyanide, including cyanuric chloride, cyanogen chloride, and many nitriles. In organic synthesis, cyanide, which is classified as a strong nucleophile, is used to prepare nitriles, which occur widely in many specialty chemicals, including pharmaceuticals.
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