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| {{otheruses1|the chemical compound}} | |||
| [[Image:Cyanide-montage.png|thumb|right|150px|The '''cyanide''' ion, CN<sup>−</sup>.<br> | |||
| From the top:<br> | |||
| 1. Valence-bond structure<br> | |||
| 2. ]<br> | |||
| 3. Electrostatic potential surface<br> | |||
| 4. 'Carbon lone pair' ]]] | |||
| A '''cyanide''' is any ] that contains the ] (C≡N), which consists of a ] ] ] to a ] atom. Inorganic cyanides are ] salts in which cyanide is generally the ] CN<sup>-</sup>. ]s that have a -C≡N ] bonded to an alkyl residue are called ]s in ] nomenclature. The ] CN is commonly produced in reactions{{Fact|date=October 2008}} and has been identified in interstellar space.<ref>{{cite paper |last=Pieniazek |first=Piotr A. |coauthors=Bradforth, Stephen E.; Krylov, Anna I. |title=Spectroscopy of the Cyano Radical in an Aqueous Environment |date=2005-12-07 |publisher=Department of Chemistry, ] |location=], ] 90089-0482 |url=http://www-bcf.usc.edu/~krylov/pubs/pdf/jpca-110-4854.pdf |format=PDF |doi=10.1021/jp0545952}}</ref> Of the many kinds of cyanide compounds, some are gases; others are solids or liquids. Those that can release the cyanide ] CN<sup>-</sup> are highly toxic. | |||
| An example of a nitrile is CH<sub>3</sub>CN, ] or ethanenitrile per IUPAC, also known as ] cyanide. Nitriles do not release cyanide ions. A functional group with a hydroxyl and cyanide on the same carbon is called ], and it is hydrolyzed into ] and a carbonyl compound (ketone or aldehyde). | |||
| Cyanide is the key to happiness. | |||
| ==Appearance and odor== | |||
| ] (HCN) is a colorless ] with a faint ]-like odor. Most people can smell hydrogen cyanide; however, due to an apparent ] trait, some individuals cannot.<ref>], </ref> ] and ] are both white ] with a bitter-almond-like odor in damp air, due to the presence of hydrogen cyanide formed by ]: | |||
| ::NaCN + H<sub>2</sub>O → HCN + NaOH | |||
| ::KCN + H<sub>2</sub>O → HCN + KOH | |||
| ==Occurrence== | |||
| Cyanides are produced by certain ], ], and ] and are found in a number of foods and plants. Cyanides are found, although in small amounts, in ] seeds, ] stones, ] stones and ].<ref>{{cite web |url=http://www.atsdr.cdc.gov/tfacts8.html |title=ToxFAQs for Cyanide |accessdate=2008-06-28 |date=July 2006 |publisher= | |||
| ]}}</ref> In plants, cyanides are usually bound to ] molecules in the form of cyanogenic ]s and defend the plant against ]s. ] roots (also called manioc), an important ]-like food grown in tropical countries (and the base from which ] is made), contains cyanogenic glycosides.<ref>{{cite journal |first=J. |last=Vetter |title=Plant cyanogenic glycosides |journal=Toxicon |year=2000 |volume=38 |pages=11–36 |doi=10.1016/S0041-0101(99)00128-2 |pmid=10669009}}</ref><ref name=jones>{{cite journal |first=D. A. |last=Jones |title= Why are so many food plants cyanogenic? |journal=] |year=1998 |volume=47 |pages=155–162 |doi=10.1016/S0031-9422(97)00425-1 |pmid=9431670}}</ref> | |||
| The Fe-only and -] ]s contain cyanide ]s at their active sites. The biosynthesis of cyanide in the -hydrogenases proceeds from ]phosphate, which converts to ]yl ], the CN<sup>-</sup> donor.<ref>{{cite journal |last=Reissmann |first=Stefanie |coauthors=Elisabeth Hochleitner, Haofan Wang, Athanasios Paschos, Friedrich Lottspeich, Richard S. Glass and August Böck |title=Taming of a Poison: Biosynthesis of the NiFe-Hydrogenase Cyanide Ligands |url=http://www.sciencemag.org/cgi/content/abstract/299/5609/1067 |accessdate=2008-06-28 |journal=] |year=2003 |volume=299 |issue=5609 |pages=1067–1070 |doi=10.1126/science.1080972 |pmid=12586941}}</ref> | |||
| Hydrogen cyanide is a product of certain kinds of ] and consequently it occurs in the ] of ]s, ] smoke, and certain ]s, especially those derived from ]. {{Fact|date=August 2007}} | |||
| ==Coordination chemistry== | |||
| The cyanide anion is considered, in a broad sense, to be the most potent ] for many transition metals. The very high affinities of metals for this ] can be attributed to its negative charge, compactness, and ability to engage in π-bonding. Well known complexes include: | |||
| *hexacyanides <sup>3−</sup> (M = Ti, V, Cr, Mn, Fe, Co), which are octahedral in shape; | |||
| *the tetracyanides, <sup>2−</sup> (M = Ni, Pd, Pt), which are square planar in their geometry; | |||
| *the dicyanides <sup>−</sup> (M = Cu, Ag, Au), which are linear in geometry. | |||
| The deep ] pigment ], used in the making of ]s, is derived from ] cyanide complexes (hence the name ''cyanide'', from ], a shade of blue). Prussian blue can produce hydrogen cyanide when exposed to acids. | |||
| ==Organic derivatives== | |||
| {{main|Nitriles}} | |||
| Because of the cyanide anion's high ], a cyano group is readily introduced into organic molecules by displacement of a ] group (i.e. the ] on ]). Organic cyanides are generally called nitriles. Thus, CH<sub>3</sub>CN can be methyl cyanide but more commonly is referred to as ]. In organic synthesis, cyanide is used as a C-1 ]. I.e., it can be used to lengthen a carbon chain by one, while retaining the ability to be functionalized. | |||
| :RX + CN<sup>−</sup> → RCN + X<sup>−</sup> (]) followed by | |||
| # RCN + 2 H<sub>2</sub>O → ] + NH<sub>3</sub> (] under reflux with mineral acid catalyst), or | |||
| # RCN + ] + (second step) 2 H<sub>2</sub>O → ] + 0.5 LiAl(OH)<sub>4</sub> (under ] in dry ], followed by addition of H<sub>2</sub>O) | |||
| An alternative method for introducing a cyano group is via the process of hydrocyanation, whereby hydrogen cyanide and alkenes combine: | |||
| RCH=CH<sub>2</sub> + HCN → RCH(CN)CH<sub>3</sub> | |||
| Metal catalysts are required for such reactions. | |||
| ==Applications== | |||
| ] is used to achieve a blue color on cast ]s 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 ] is occasionally used in emergency medical situations to produce a rapid decrease in ] in humans; it is also used as a ] in vascular research. The cobalt in artificial ] contains a cyanide ligand as an artifact of the purification process. During ], a copper cyanide compound was briefly used by ]ese physicians for the treatment of tuberculosis and leprosy.<ref>{{cite journal |last=Takano |first=R. |year=1916 |month=August |title=The treatment of leprosy with cyanocuprol |journal=The Journal of Experimental Medicine |volume=24 |issue= |pages=207–211 |url=http://www.jem.org/cgi/content/abstract/24/2/207 |accessdate=2008-06-28 |doi=10.1084/jem.24.2.207 |pmc=2125457}}</ref> | |||
| ===Mining=== | |||
| ] and ] cyanides are among the very few ] forms of these metals, and cyanides are thus used in ] as well as ], ], ], and ]. In the so-called '']'', 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 a cyanide solution (concentration of about one kilogram NaCN per ton). The precious-metal ]s are complexed by the cyanide ]s to form soluble derivatives, e.g. <sup>−</sup> and <sup>−</sup>. | |||
| ::2 Au + 4 KCN + ½ O<sub>2</sub> + H<sub>2</sub>O → 2 K + 2 KOH | |||
| ::2 Ag + 4 KCN + ½ O<sub>2</sub> + H<sub>2</sub>O → 2 K + 2 KOH | |||
| Silver is less "noble" than gold and often occurs as the sulfide, in which case redox is not invoked (no O<sub>2</sub> is required), instead a displacement reaction occurs: | |||
| ::Ag<sub>2</sub>S + 4 KCN → 2 K + K<sub>2</sub>S | |||
| 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 ] 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 ] (fool's gold), wherein half of the sulfur atoms are replaced by ]. Gold-containing arsenopyrite ores are similarly reactive toward inorganic cyanide. | |||
| ===Fishing=== | |||
| {{main|Cyanide fishing}} | |||
| {{Cleanup|section|date=August 2008}} | |||
| {{Original research|section|date=April 2009}} | |||
| Cyanides are illegally used to capture live fish near ]s for the ] and seafood markets. This fishing occurs mainly in the ], ] and the ] to supply the 2 million marine ] owners in the world. In this method, a diver uses a large, needleless ] 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. . | |||
| Magnesium cyanide is also used in some countries illegally to stun and harvest ] fish. | |||
| ===Fumigation=== | |||
| Cyanides are used as ]s for the fumigating of ships. Cyanide salts are used for killing ants, and have in some places been used as rat poison (the less toxic poison ] is more common{{Fact|date=October 2008}}). | |||
| ==Chemical tests for cyanide== | |||
| ===Prussian blue=== | |||
| The formation of ] can be used as a test for inorganic cyanide, for instance in the ]. Typically, ] is added to a solution suspected of containing cyanide, such as the filtrate from the ]. The resulting mixture is acidified with ]. The formation of ] is a positive result for cyanide. | |||
| ===''para''-Benzoquinone in DMSO=== | |||
| A solution of ''para''-] in ] reacts with inorganic cyanide to form a cyano], which is ]. Illumination with a ] gives a green/blue glow if the test is positive. | |||
| ===Copper and an aromatic amine=== | |||
| As used by ] to detect ], ](II) salt and an aromatic amine such as ] is added to the sample; as an alternative to benzidine an alternative amine di-(4,4-''bis''-dimethylaminophenyl) methane can be used. A positive test gives a blue color. ] is poorly soluble. By ] the copper(I) the copper(II) is rendered a stronger ]. The copper, in a cyanide facilitated oxidation, converts the ] into a colored compound. The ] explains this process. Another good example of such chemistry is the way in which the saturated ] ] (]) works. The copper, in a cyanide facilitated oxidation converts the ] into a colored compound. | |||
| ===Pyridine-barbituric acid colorimetry=== | |||
| A sample containing inorganic cyanide is purged with air from a boiling acid solution into a basic absorber solution. The cyanide salt absorbed in the basic solution is buffered at pH 4.5 and then reacted with chlorine to form cyanogen chloride. The cyanogen chloride formed couples pyridine with barbituric acid to form a strongly colored red dye that is proportional to the cyanide concentration. This colorimetric method following distillation is the basis for most regulatory methods (for instance EPA 335.4) used to analyze cyanide in water, wastewater, and contaminated soils. Distillation followed by colorimetric methods, however, have been found to be prone to interferences from thiocyanate, nitrate, thiosulfate, sulfite, and sulfide that can result in both positive and negative bias. It has been recommended by the USEPA (MUR March 12, 2007) that samples containing these compounds be analyzed by Gas-Diffusion Flow Injection Analysis — Amperometry.{{Fact|date=June 2008}} | |||
| ===Gas diffusion flow injection analysis — amperometry=== | |||
| Instead of distilling, the sample is injected into an acidic stream where the HCN formed is passed under a hydrophobic gas diffusion membrane that selectively allows only HCN to pass through. The HCN that passes through the membrane is absorbed into a basic carrier solution that transports the CN to an amperometric detector that accurately measures cyanide concentration with high sensitivity. Sample pretreatment determined by acid reagents, ligands, or preliminary UV irradiation allow cyanide speciation of free cyanide, available cyanide, and total cyanide respectively. These relative simplicity of these flow injection analysis methods limit the interference experienced by the high heat of distillation and also prove to be cost effective since time consuming distillations are not required. | |||
| ==Toxicity== | |||
| {{main|Cyanide poisoning}} | |||
| Many cyanide-containing compounds are highly toxic, but some are not. ], with an approximate formula Fe<sub>7</sub>(CN)<sub>18</sub> is the blue of ]s and is administered orally as an antidote to poisoning by ] and radioactive ]. The most dangerous cyanides are ] (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 ] (CH<sub>3</sub>)<sub>3</sub>SiCN upon contact with water and ]s upon ]. {{Fact|date=February 2007}} | |||
| The cyanide anion is an ] of the ] ] (also known as aa<sub>3</sub>) in the fourth complex of the ] (found in the membrane of the ] of eukaryotic cells). It attaches to the iron within this protein. The binding of cyanide to this cytochrome prevents transport of electrons from ] to oxygen. As a result, the electron transport chain is disrupted, meaning that the cell can no longer aerobically produce ] for energy. Tissues that mainly depend on ], such as the ] and the ], are particularly affected. Antidotes to cyanide poisoning include ] and ] which release the cyanide from the cytochrome system, and ], which is an enzyme occurring naturally in mammals that combines serum cyanide with thiosulfate, producing comparatively harmless thiocyanate. | |||
| Cyanides have been used as poison many times throughout history. Its most infamous application was the use of hydrogen cyanide by the ] regime in Germany for mass murder in some ]s during ]. Cyanides have been used for murder, as in the case of ] and have also been used for suicide. Some notable cases are ], ], ], ], ], ], ], ] (in combination with a gunshot), the residents of ] and the ]. | |||
| ==References== | |||
| {{reflist|2}} | |||
| ==Sources== | |||
| {{More footnotes|date=October 2008}} | |||
| *Institut national de recherche et de sécurité (1997). "". ''Fiche toxicologique n° 4'', Paris:INRS, 5pp. (PDF file, ''in French'') | |||
| *Institut national de recherche et de sécurité (1997). "". ''Fiche toxicologique n° 111'', Paris:INRS, 6pp. (PDF file, ''in French'') | |||
| ==External links== | |||
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| * , by Charles Stewart | |||
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| * (] 61) | |||
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