Sodium cyanide is the inorganic compound with the formula NaCN. This highly toxic salt is used mainly in gold mining but have other niche applications. It is also called cyanogran.
Production and chemical properties
Sodium cyanide is produced by treating the weak acid hydrogen cyanide with sodium hydroxide:[1]
- HCN + NaOH → NaCN + H2O
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.
- NaNH2 + C → NaCN + H2
As the salt is derived from a weak acid, NaCN readily undergoes 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[2]). 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:[1]
- NaCN + H2O2 → NaOCN + H2O
Applications
Cyanide mining
- Further information: cyanide process
Sodium cyanide is mainly used to extract gold and other precious metals in mining. This application takes advantage of the high affinity of gold(I) for cyanide, which induces gold metal to oxidize and dissolve in the presence of air and water.
- 4 Au + 8 NaCN + O2 + 2 H2O → 4 Na[Au(CN)2 + 4 NaOH
Very few alternative methods exist for this extraction process.
Chemical feedstock
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.
Niche uses
Being highly toxic, sodium cyanide is used to kill or stun rapidly such as in illegal cyanide fishing and by entomologists as a killing agent in collecting jars.
Toxicity
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Cyanide salts are among the most rapidly acting of all known poisons. Cyanide is a potent inhibitor of respiration, acting on mitochondrial cytochrome oxidase and hence blocking electron transport. This results in decreased oxidative metabolism and oxygen utilization. Lactic acidosis then occurs as a consequence of anaerobic metabolism.
References
- ^ a b Andreas Rubo, Raf Kellens, Jay Reddy, Norbert Steier, Wolfgang Hasenpusch "Alkali Metal Cyanides" in Ullmann's Encyclopedia of Industrial Chemistry 2006 Wiley-VCH, Weinheim, Germany.ISBN: 10.1002/14356007.i01 i01
- ^ Online 'Mendelian Inheritance in Man' (OMIM) 304300
See also
External links
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