Dictionary: cyanide   (sī'ə-nīd')

Any of various salts or esters of hydrogen cyanide containing a CN group, especially the extremely poisonous compounds potassium cyanide and sodium cyanide.

1. To treat (a metal surface) with cyanide to produce a hard surface.
2. To treat (an ore) with cyanide to extract gold or silver.

A compound containing the CN group, for example, potassium cyanide, KCN; calcium cyanide, Ca(CN)₂; and hydrocyanic (or prussic) acid, HCN. Chemically, the simple inorganic cyanides resemble chlorides in many ways. Organic compounds containing this group are called nitriles, for example, acrylonitrile, CH₂CHCN. See also Acrylonitrile.

HCN is a weak acid. In the pure state, it is a highly volatile liquid, boiling at 26°C (78.8°F). HCN and the cyanides are highly toxic to animals and humans.

The cyanide ion forms a variety of coordination complexes with transition-metal ions, a property responsible for several of the commercial uses of cyanides. The cyanide process T is the most widely used method for extracting gold and silver from the ores. In silver-plating, a smooth adherent deposit is obtained on a metal cathode when electrolysis is carried out in the presence of an excess of cyanide ion.

Ca(CN)₂ is extensively used in pest control and as a fumigant in the storage of grain. In finely divided form, it reacts slowly with the moisture in the air to liberate HCN.

In case hardening of metals, an iron or steel article is immersed in a bath of molten sodium or potassium cyanide containing sodium chloride or carbonate. The cyanide decomposes at the surface, forming a deposit of carbon which combines with and penetrates the metal. See also Coordination chemistry.

For more information on cyanide, visit Britannica.com.

The prospects for an intelligence operative captured by enemy forces are grim. Soldiers and other war fighters have recourse to Geneva Convention protocols concerning treatment, but personnel working in intelligence and covert operations are effectively denied such protection by virtue of their mission's clandestine nature. The best hope is to be released in a prisoner exchange, sometimes after years. Even then, imprisonment in many countries is likely to include lengthy and exposure to coercive methods, including beatings and/or torture whose intention is to induce the operative to divulge sensitive information. For some, the risk is too great, and therefore, intelligence operatives and agents have often gone into dangerous situations equipped with suicide devices. Most of these employ one form of disguise or another to hide a deadly compound of nitrogen, carbon, and other elements known as cyanide.

The chemistry and biological effects of cyanide. When an atom of carbon bonds with an atom of nitrogen, that is cyanide, an ionic compound designated as CN—hence the name cyanide. The bonding of these atoms with other elements produces various forms: hydrogen cyanide (HCN), cyanogen chloride (CNCl), sodium cyanide (NaCN), or potassium cyanide (KCN). The first two are colorless gases, while the second two appear in crystal form. In addition to these chemical formulas, cyanide is sometimes referred to by military organizations as AN (hydrogen cyanide) or CK (cyanogen chloride).

Applied in materials for exterminating rats and other pests, removing artificial nails, or developing photographs, cyanide has a number of practical uses. It is found in some foods, most notably cassava, and when combined with another chemical, it produces a life-sustaining substance, vitamin B¹². Yet even in small quantities, cyanide is harmful, a fact illustrated by poisoning deaths in parts of Africa where the diet is heavy in cassava. Cyanide is also one of the most dangerous toxins in cigarette smoke, which is the form of cyanide to which the average person is most likely to be exposed.

Cyanide prevents the body's cells from receiving oxygen, and particularly effects the heart and brain because those two vital organs are particularly dependent on the body's oxygen supply. Within minutes, the victim of cyanide poisoning in very small quantities will begin breathing rapidly and display signs of restlessness. Other symptoms include dizziness, weakness, headache, nausea and vomiting, and a rapid heart rate. Exposure to larger amounts causes rapid convulsions, severe lowering of blood pressure and heart rate, loss of consciousness, lung injury, and ultimately respiratory failure that leads to death.

Cyanide in history. Because cyanide is an effective killer, Iraqi dictator Saddam Hussein included hydrogen cyanide among the chemical weapons he used against the Kurds in the Iran-Iraq war of the 1980s. Forty years earlier, during World War II, Nazi Germany used hydrogen cyanide—in the form of Zyklon B—as an even more efficient agent of genocide in its death camps, where it killed millions of Jews and others. Ironically, in the same war, the Nazis' enemies carried cyanide pills on their persons for a very different reason, to eliminate themselves if captured.

Personnel working for the Special Operations Executive (SOE) in the war were often equipped with "L" pills (L for lethal) containing cyanide in crystal form. In some cases, cyanide could be hidden in the earpiece of a pair of glasses. When cornered, the operative could take off his glasses and pretend to thoughtfully bite the end of the earpiece while thinking about what he would say next. But there would not be any next statement: within seconds of consuming this deadly toxin, the operative would be dead.

A similar situation happened in 1977, when Soviet diplomat Aleksandr Ogorodnik found that he had reached the end of the line. He had been secretly working for the U.S. Central Intelligence Agency, who knew him by the code name TRIGON. When the Soviets discovered they had a traitor in their midst, they presented him with a confession to sign. Ogorodnik, well aware of what lay in store for him, asked to use his own pen, and when it was given to him, he bit off the end, ingesting a dose of cyanide hidden there. Within seconds, he was dead.

In order to keep this means of escape handy, operatives have gone to extraordinary lengths. Among the items used for concealing cyanide pills in the past is a container shaped like a cigarette lighter and made to fit in the rectum. In 1960, U-2 pilot Francis Gary Powers carried a cyanide capsule on his person. Instead of committing suicide, when the Soviets shot down his plane, Powers parachuted to earth, and was taken prisoner. Later, after his captors had reaped enormous propaganda benefits from the incident, he was traded for a Soviet spy in a prisoner exchange.

Further Reading

Books

Melton, H. Keith. The Ultimate Spy Book. New York: DK Publishing, 1996.

Minnery, John. CIA Catalog of Clandestine Weapons, Tools, and Gadgets. Boulder, CO: Paladin Press, 1990.

Electronic

Facts About Suicide. Centers for Disease Control. <http://www.bt.cdc.gov/agent/cyanide/index.asp> (March 19, 2003).

International Spy Museum. <http://www.spymuseum.org> (March 19, 2003).

A binary compound of cyanogen. Some inorganic compounds, such as cyanide salts, potassium cyanide and sodium cyanide, are important in industry for extracting gold and silver from their ores and in electroplating. Other cyanide compounds are used in the manufacture of synthetic rubber and textiles. Cyanides are also used in pesticides.
There are many potential sources of cyanide in the environment of farm animals. Cyanide poisoning occurs most commonly when cattle gain access to a bulk supply of a cyanogenetic plant, e.g. sudan grass, immature sorghum. Typical clinical signs are dyspnea within a few minutes of getting access to the food, restlessness, recumbency and death within a matter of 15 minutes to 2 hours. The cyanide is not free in the plants but is combined with a glycoside radical and must be degraded by ruminal enzymes to release its HCN. Called also hydrocyanic acid. See cyanogenetic glycosides.

Hydrogen cyanide reportedly was used by Iraq in the war against Iran and against the Kurds in northern Iraq during the 1980's. The Nazis used a form of hydrogen cyanide (Zyklon B) the gas chambers of their concentration camps. It colorless liquid which may be inhaled in gaseous form. Cyanide salts and liquid cyanide may be absorbed by the skin. Symptoms are dizziness, headache, palpitations and respiratory difficulty. These are later followed by vomiting, convulsions, respiratory failure, unconsciousness, and death.

This article is about the chemical compound. For other uses, see Cyanide (disambiguation).

The cyanide ion, CN⁻.
From the top:
1. Valence-bond structure
2. Space-filling model
3. Electrostatic potential surface
4. 'Carbon lone pair' HOMO

A cyanide is any chemical compound that contains the cyano group (C≡N), which consists of a carbon atom triple-bonded to a nitrogen atom. Cyanide specifically is the anion CN^-. Many organic compounds feature cyanide as a functional group; these are called nitriles in IUPAC nomenclature (for example, CH₃CN is referred to by the names acetonitrile or ethanenitrile per IUPAC, but occasionally it is labeled using the common name methyl cyanide). Of the many kinds of cyanide compounds, some are gases, others are solids or liquids. Some are molecular, some ionic, and many are polymeric. Those that can release the cyanide ion CN^- are highly toxic.

The word "cyanide" comes from the Greek word for "blue", in reference to HCN, which was called Blausäure ("blue acid") in German after its preparation by acid treatment of Berlin blue.^[1]

Appearance and odor

Hydrogen cyanide (HCN) is a colorless gas with a faint bitter almond-like odor. Most people can smell hydrogen cyanide; however, due to an apparent genetic trait, some individuals cannot detect the odor of HCN.^[2] Sodium cyanide and potassium cyanide are both white powders with a bitter almond-like odor in damp air, due to the presence of hydrogen cyanide formed by hydrolysis:

NaCN + H₂O → HCN + NaOH

Occurrence

Cyanides are produced by certain bacteria, fungi, and algae and are found in a number of foods and plants. Cyanide is found, although in small amounts, in apple seeds and almonds.^[3] In plants, cyanides are usually bound to sugar molecules in the form of cyanogenic glycosides and serve the plant as defense against herbivores. Cassava roots (aka manioc), an important potato-like food grown in tropical countries (and the base from which tapioca is made), contains cyanogenic glycosides^[4][5].

The Fe-only and [NiFe]-hydrogenase enzymes contain cyanide ligands at their active sites. The biosynthesis of cyanide in the [NiFe]-hydrogenases proceeds from carbamoylphosphate, which converts to cysteinyl thiocyanate, the CN^- donor. ^[6]

Hydrogen cyanide is a product of certain kinds of pyrolysis and consequently it occurs in the exhaust of internal combustion engines, tobacco smoke, and certain plastics, especially those derived from acrylonitrile.^{[citation needed]}

Coordination chemistry

Cyanide is considered, in a broad sense, to be the most potent ligand for many transition metals. The very high affinities of metals for cyanide can be attributed to its negative charge, compactness, and ability to engage in π-bonding. Well known complexes include:

• hexacyanides [M(CN)₆]³⁻ (M = Ti, V, Cr, Mn, Fe, Co), which are octahedral in shape;
• the tetracyanides, [M(CN)₄]²⁻ (M = Ni, Pd, Pt), which are square planar in their geometry;
• the dicyanides [M(CN)₂]⁻ (M = Cu, Ag, Au), which are linear in geometry.

The deep blue pigment Prussian blue, used in the making of blueprints, is derived from iron cyanide complexes (hence the name cyanide, from cyan, a shade of blue). Prussian blue can produce hydrogen cyanide when exposed to acids.

Organic synthesis

Main article: Nitriles

Because of its high nucleophilicity, cyanide is readily introduced into organic molecules by displacement of a halide group (i.e. The Chloride on Methyl Chloride). Organic cyanides are generally called nitriles. Thus, CH₃CN can be methyl cyanide but more commonly is referred to as acetonitrile. In organic synthesis, cyanide is used as a C-1 synthon. I.e., it can be used to lengthen a carbon chain by one, while retaining the ability to be functionalized.

RX + CN⁻ → RCN + X⁻ (Nucleophilic Substitution) followed by

1. RCN + 2 H₂O → RCOOH + NH₃ (Hydrolysis under reflux with mineral acid catalyst), or
2. RCN + 0.5 LiAlH₄ + (second step) 2 H₂O → RCH₂NH₂ + 0.5 LiAl(OH)₄ (under reflux in dry ether, followed by addition of H₂O)

An alternative method for introducing cyanide is via the process of hydrocyanation, whereby hydrogen cyanide and alkenes combine: RCH=CH₂ + HCN → RCH(CN)CH₃ Metal catalysts are required for such reactions.

Applications

Potassium ferrocyanide is used to achieve a blue colour on cast bronze sculptures during the final finishing stage of the sculpture. On its own, it will produce a very dark shade of blue and is often mixed with other chemicals to achieve the desired tint and hue. It is applied using a torch and paint brush while wearing the standard safety equipment used for any patina application: rubber gloves, safety glasses, and a respirator. The actual amount of cyanide in the mixture varies according to the recipes used by each foundry.

Medical uses

The cyanide compound sodium nitroprusside is occasionally used in emergency medical situations to produce a rapid decrease in blood pressure in humans; it is also used as a vasodilator in vascular research.

Mining

Gold and silver cyanides are among the very few soluble forms of these metals, and cyanides are thus used in mining as well as electroplating, metallurgy, jewelry, and photography. In the so-called cyanide process, finely ground high-grade ore is mixed with the cyanide (concentration of about two kilogram NaCN per tonne); low-grade ores are stacked into heaps and sprayed with cyanide solution (concentration of about one kilogram NaCN per ton). The precious-metal cations are complexed by the cyanide anions to form soluble derivatives, e.g. [Au(CN)₂]⁻ and [Ag(CN)₂]⁻.

2 Au + 4 KCN + ½ O₂ + H₂O → 2 K[Au(CN)₂] + 2 KOH

2 Ag + 4 KCN + ½ O₂ + H₂O → 2 K[Ag(CN)₂] + 2 KOH

Silver is less "noble" than gold and often occurs as the sulfide, in which case redox is not invoked (no O₂ is required), instead a displacement reaction occurs:

Ag₂S + 4 KCN → 2 K[Ag(CN)₂] + K₂S

The "pregnant liquor" containing these ions is separated from the solids, which are discarded to a tailing pond or spent heap, the recoverable gold having been removed. The metal is recovered from the "pregnant solution" by reduction with zinc dust or by adsorption onto activated carbon. This process can result in environmental and health problems. Aqueous cyanide is hydrolyzed rapidly, especially in sunlight. It can mobilize some heavy metals such as mercury if present. Gold can also be associated with arsenopyrite (FeAsS), which is similar to iron pyrite (fool's gold), wherein half of the sulfur atoms are replaced by arsenic. Au-containing arsenopyrite ores are similarly reactive toward cyanide.

Fishing

Main article: Cyanide fishing

Cyanides are illegally used to capture live fish near coral reefs for the aquarium and seafood markets. This fishing occurs mainly in the Philippines, Indonesia and the Caribbean to supply the 2 million marine aquarium owners in the world. In this method, a diver uses a large, needleless syringe to squirt a cyanide solution into areas where the fish are hiding, stunning them so that they can be easily gathered. Many fish caught in this fashion die immediately, or in shipping. Those that survive to find their way into pet stores often die from shock, or from massive digestive damage. The high concentrations of cyanide on reefs on which this has occurred has resulted in cases of cyanide poisoning among local fishermen and their families, as well as irreversible damage to the coral reefs themselves and other marine life in the area.

Environmental organizations are critical of the practice, as are some aquarists and aquarium dealers, to prevent the trade of illegally-caught aquarium fish. The Marine Aquarium Council (Headquarters: Honolulu, Hawaii) has created a certification in which the tropical fish are caught legally with nets only. To ensure authenticity, "MAC-Certified marine organisms bear the MAC-Certified label on the tanks and boxes in which they are kept and shipped." MAC Certification.

Magnesium cyanide is also used in some countries illegally to stun and harvest stream fish.

Fumigation

Cyanides are used as insecticides for the fumigating of ships. In the past cyanide salts have and still are in some places being used as rat poison.

Toxicity

Main article: Cyanide poisoning

Many cyanide-containing compounds are highly toxic, but many are not. Prussian blue, with an approximate formula Fe₇(CN)₁₈ is the blue of blue prints and is administered orally as an antidote to poisoning by thallium and Caesium-137. The most dangerous cyanides are hydrogen cyanide (HCN) and salts derived from it, such as potassium cyanide (KCN) and sodium cyanide (NaCN), among others. Also some compounds readily release HCN or the cyanide ion, such as trimethylsilyl cyanide (CH₃)₃SiCN upon contact with water and cyanoacrylates upon pyrolysis. ^{[citation needed]}

Cyanide is an irreversible inhibitor of the enzyme cytochrome c oxidase (also known as aa₃) in the fourth complex in the membrane of the mitochondria of cells. It attached to the iron within this protein. The binding of cyanide to this cytochrome prevents transport of electrons from cytochrome c oxidase to oxygen. As a result, the electron transport chain is disrupted, meaning that the cell can no longer aerobically produce ATP for energy. Tissues that mainly depend on aerobic respiration, such as the central nervous system and the heart, are particularly affected.

Cyanides have been used as a poison many times throughout history. Its most infamous application was the use of hydrogen cyanide by the Nazi regime in Germany for mass murder in some gas chambers during the Holocaust. Cyanide has been used for murder, as in the case of Rasputin. It has also been used for suicide. Some notable cases are Erwin Rommel, Eva Braun, Adolf Hitler, Wallace Carothers, Hermann Göring, Heinrich Himmler, Alan Turing, and Odilo Globocnik. Finally, cyanide is a very common poison in crime fiction.

References

1. ^ Alexander Senning. Elsevier's Dictionary of Chemoetymology. Elsevier, 2006. ISBN 0444522395.
2. ^ Online Mendelian Inheritance in Man, Cyanide, inability to smell
3. ^ Agency for Toxic Substances and Disease Registry, ToxFaqs for Cyanide, Jul 2006.
4. ^ J. Vetter (2000). "Plant cyanogenic glycosides". Toxicon. 38: 11-36. DOI:10.1016/S0041-0101(99)00128-2. 
5. ^ D. A. Jones (1998). "Why are so many food plants cyanogenic?". Phytochemistry 47: 155-162. DOI:10.1016/S0031-9422(97)00425-1. 
6. ^ Reissmann, S.; Hochleitner, E.; Wang, H.; Paschos, A.; Lottspeich, F.; Glass, R. S. and Böck, A. (2003). "Taming of a Poison: Biosynthesis of the NiFe-Hydrogenase Cyanide Ligands". Science 299 (5609): 1067-70. DOI:10.1126/science.1080972. 

Sources

• Institut national de recherche et de sécurité (1997). "Cyanure d'hydrogène et solutions aqueuses". Fiche toxicologique n° 4, Paris:INRS, 5pp. (PDF file, in French)
• Institut national de recherche et de sécurité (1997). "Cyanure de sodium. Cyanure de potassium". Fiche toxicologique n° 111, Paris:INRS, 6pp. (PDF file, in French)

External links

• ATSDR medical management guidelines for cyanide poisoning (US)
• Cyanide intoxication, by Charles Stewart
• HSE recommendations for first aid treatment of cyanide poisoning (UK)
• Hydrogen cyanide and cyanides (CICAD 61)
• IPCS/CEC Evaluation of antidotes for poisoning by cyanides
• National Pollutant Inventory - Cyanide compounds fact sheet
• Eating apple seeds is safe despite the small amount of cyanide

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Dansk (Danish)
n. - cyanid
v. tr. - anvende cyanidmetoden, indsætte cyan

Nederlands (Dutch)
cyanide

Français (French)
n. - (Chim) cyanure
v. tr. - durcir un métal par dissolution dans une solution de cyanure, extraire de l'or par dissolution dans une solution de cyanure

Deutsch (German)
n. - Zyanid
v. - zementieren, im Cyanidverfahren bearbeiten

Ελληνική (Greek)
n. - (χημ.) κυανιούχο άλας, άλας του υδροκυάνιου, υδροκυάνιο

Italiano (Italian)
cianuro

Português (Portuguese)
n. - cianeto (m) (Quím.)

Русский (Russian)
цианид

Español (Spanish)
n. - cianuro
v. tr. - tratar con cianuro para extraer oro

Svenska (Swedish)
n. - cyanid

中文（简体） (Chinese (Simplified))
氰化物, 用氰化物处理

中文（繁體） (Chinese (Traditional))
n. - 氰化物
v. tr. - 用氰化物處理

한국어 (Korean)
n. - 시안 화물, 청산가리
v. tr. - 시안으로 처리하다

日本語 (Japanese)
n. - シアン化物

العربيه (Arabic)
‏(الاسم) مادة السيانيد ( كيمياء)‏

עברית (Hebrew)
n. - ‮ציאניד (רעל)‬
v. tr. - ‮השתמש בציאניד כבמחצב להפקת זהב, הרעיל‬

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