The Full Wiki

Cyanide: Wikis


Note: Many of our articles have direct quotes from sources you can cite, within the Wikipedia article! This article doesn't yet, but we're working on it! See more info or our list of citable articles.

Did you know ...

  • in gold mining, cyanide may be used to extract gold in areas where gold-bearing rocks are found at the surface?

More interesting facts on Cyanide

Include this on your site/blog:


From Wikipedia, the free encyclopedia

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. Inorganic cyanides are generally salts of the anion CN.[1][2] Organic compounds that have a –C≡N functional group are called nitriles. Of the many kinds of cyanide compounds, some are gases; others are solids or liquids. Those that can release the cyanide ion CN are highly toxic to animals.[3]

An example of a nitrile is CH3CN, acetonitrile (ethanenitrile per IUPAC), also known as methyl cyanide. Nitriles do not release cyanide ions. A functional group with a hydroxyl and cyanide bonded to the same carbon is called cyanohydrin, and cyanohydridins are hydrolyzed into hydrogen cyanide and a carbonyl compound (ketone or aldehyde).



The word "cyanide" was derived from "ferrocyanide", a cyanide derivative of iron. Iron cyanides were first discovered as components on the intensely colored dye Prussian blue. Kyaneos is Greek for "(dark) blue".[4]


Cyanides are produced by certain bacteria, fungi, and algae and are found in a number of foods and plants. Cyanides are found, although in small amounts, in certain seeds and stones, e.g. those of apple, mango, peach, and bitter almonds.[5] In plants, cyanides are usually bound to sugar molecules in the form of cyanogenic glycosides and defend the plant against herbivores. Cassava roots (also called manioc), an important potato-like food grown in tropical countries (and the base from which tapioca is made), also contain cyanogenic glycosides.[6][7]

The cyanide radical CN· has been identified in interstellar space.[8]

Hydrogen cyanide is produced by the combustion or pyrolysis of certain materials under oxygen-deficient conditions. For example it can be detected in the exhaust of internal combustion engines and tobacco smoke. Certain plastics, especially those derived from acrylonitrile, release hydrogen cyanide when heated or burnt.

Coordination chemistry

The cyanide anion is a potent ligand for many transition metals.[9] The very high affinities of metals for this anion 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 strong acids.

Certain enzymes, the hydrogenase, contain cyanide ligands attached to iron in their active sites. The biosynthesis of cyanide in the [NiFe]-hydrogenases proceeds from carbamoylphosphate, which converts to cysteinyl thiocyanate, the CN donor.[10]

Organic derivatives

Because of the cyanide anion's high nucleophilicity, a cyano group is readily introduced into organic molecules by displacement of a halide group (e.g. 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)



Cyanide is mainly produced for the mining of gold and silver: it helps dissolve these metals and their ores. 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 a cyanide solution (concentration of about one kilogram NaCN per ton). The precious metal are complexed by the cyanide anions to form soluble derivatives, e.g. [Au(CN)2] and [Ag(CN)2].[11]

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. Gold-containing arsenopyrite ores are similarly reactive toward inorganic cyanide.

Cyanide is also used in electroplating.

Industrial organic chemistry

Some nitriles are produced on a large scale, e.g. adiponitrile is a precursor to nylon. Such compounds are often generated by combining hydrogen cyanide and alkenes, i.e., hydrocyanation: RCH=CH2 + HCN → RCH(CN)CH3 Metal catalysts are required for such reactions.

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. The cobalt in artificial Vitamin B12 contains a cyanide ligand as an artifact of the purification process. During World War I, a copper cyanide compound was briefly used by Japanese physicians for the treatment of tuberculosis and leprosy.[12]


Cyanides are illegally used to capture live fish near coral reefs for the aquarium and seafood markets. The practice is controversial, dangerous, and damaging but is driven by the lucrative western market for tropical fish.

Niche uses

Potassium ferrocyanide is used to achieve a blue color 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.

Cyanide is also used in jewelry-making and certain kinds of photography.

Cyanides are used as insecticides for fumigating ships. Cyanide salts are used for killing ants, and have in some places been used as rat poison (the less toxic poison arsenic is more common).

Chemical tests for cyanide

Prussian blue

Iron(II) sulfate is added to a solution suspected of containing cyanide, such as the filtrate from the sodium fusion test. The resulting mixture is acidified with mineral acid. The formation of Prussian blue is a positive result for cyanide.

para-Benzoquinone in DMSO

A solution of para-benzoquinone in DMSO reacts with inorganic cyanide to form a cyanophenol, which is fluorescent. Illumination with a UV light gives a green/blue glow if the test is positive.[13]

Copper and an aromatic amine

As used by fumigators to detect hydrogen cyanide, copper(II) salt and an aromatic amine such as benzidine 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. Copper(I) cyanide is poorly soluble. By sequestering the copper(I) the copper(II) is rendered a stronger oxidant. The copper, in a cyanide facilitated oxidation, converts the amine into a colored compound. The Nernst equation explains this process. Another good example of such chemistry is the way in which the saturated calomel reference electrode (SCE) works. The copper, in a cyanide facilitated oxidation converts the amine 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.

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.


Many cyanide-containing compounds are highly toxic, but some are not. Nitriles (which do not release cyanide ions) and hexacyanoferrates (ferrocyanide and ferricyanide, where the cyanide is already tightly bound to an iron ion) have low toxicities, while most other cyanides are deadly poisonous. 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 radioactive caesium-137; the large ferrocyanide anion is an effective getter for heavy monovalent cations. 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.

The cyanide anion is an inhibitor of the enzyme cytochrome c oxidase (also known as aa3) in the fourth complex of the electron transport chain (found in the membrane of the mitochondria of eukaryotic cells). It attaches 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.

Antidote to poisoning

Hydroxycobalamin reacts with cyanide to form cyanocobalamin. Cyanocobalamin can be eliminated by the kidneys. This method has the advantage of avoiding the formation of methemoglobin (see below). This antidote kit is sold under the brand name Cyanokit and was approved by the FDA in 2006. An older cyanide antidote kit included administration of three substances: amyl nitrite pearls (inhalation) and sodium nitrite and sodium thiosulfate (infusion). The goal of the antidote is to generate a large pool of ferric iron to compete with cytochrome a3 (part of the electron transport chain necessary for cellular respiration/energy production) for cyanide. The nitrites oxidize hemoglobin to methemoglobin which competes with cytochrome oxidase for the cyanide ion. Cyanmethemoglobin is formed and cytochrome oxidase is restored. The major mechanism to remove the cyanide from the body is by enzymatic conversion by the mitochondrial enzyme rhodanese to convert cyanate to thiocyanate, which is a relatively non-toxic molecule that is excreted in the urine. To accelerate the detoxification sodium thiosulfate is administered to provide a sulfur donor for rhodanese to produce thiocyanate.

Notable cyanide deaths

Cyanides have been used as poison many times throughout history. The most infamous application was the use of hydrogen cyanide (in Zyklon B pellets) by the Nazi regime in Germany for mass murder in some gas chambers during the Holocaust. Cyanides have been used (as in the case of Grigori Rasputin) for attempted murder, and for judicial execution in some parts of the United States. Some notable persons who committed suicide by cyanides (either cyanide salt or hydrogen cyanide) are Eva Braun, Wallace Carothers, Odilo Globocnik, Joseph Goebbels, Hermann Göring, Heinrich Himmler, Adolf Hitler (in combination with a gunshot), Günther von Kluge, Erwin Rommel, Alan Turing, the residents of Jonestown and the Liberation Tigers of Tamil Eelam.


  1. ^ Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.
  2. ^ G. L. Miessler and D. A. Tarr “Inorganic Chemistry” 3rd Ed, Pearson/Prentice Hall publisher, ISBN 0-13-035471-6.
  3. ^ "Environmental and Health Effects of Cyanide". International Cyanide Management Institute. 2006. Retrieved 4 August 2009.  
  4. ^ Senning, Alexander (2006). Elsevier's Dictionary of Chemoetymology. Elsevier. ISBN 0444522395.  
  5. ^ "ToxFAQs for Cyanide". Agency for Toxic Substances and Disease Registry. July 2006. Retrieved 2008-06-28.  
  6. ^ Vetter, J. (2000). "Plant cyanogenic glycosides". Toxicon 38 (1): 11–36. doi:10.1016/S0041-0101(99)00128-2. PMID 10669009.  
  7. ^ Jones, D. A. (1998). "Why are so many food plants cyanogenic?". Phytochemistry 47 (2): 155–162. doi:10.1016/S0031-9422(97)00425-1. PMID 9431670.  
  8. ^ Pieniazek, Piotr A.; Bradforth, Stephen E.; Krylov, Anna I. (2005-12-07) (PDF). Spectroscopy of the Cyano Radical in an Aqueous Environment. Los Angeles, California 90089-0482: Department of Chemistry, University of Southern California. doi:10.1021/jp0545952.  
  9. ^ Sharpe, A. G. The Chemistry of Cyano Complexes of the Transition Metals; Academic Press: London, 1976
  10. ^ Reissmann, Stefanie; Elisabeth Hochleitner, Haofan Wang, Athanasios Paschos, Friedrich Lottspeich, Richard S. Glass and August Böck (2003). "Taming of a Poison: Biosynthesis of the NiFe-Hydrogenase Cyanide Ligands". Science 299 (5609): 1067–1070. doi:10.1126/science.1080972. PMID 12586941. Retrieved 2008-06-28.  
  11. ^ 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
  12. ^ Takano, R. (August 1916). "The treatment of leprosy with cyanocuprol". The Journal of Experimental Medicine 24: 207–211. doi:10.1084/jem.24.2.207. PMC 2125457. Retrieved 2008-06-28.  
  13. ^ . doi:10.1016/0041-008X(80)90225-2.  


External links

1911 encyclopedia

Up to date as of January 14, 2010
(Redirected to Database error article)

From LoveToKnow 1911

(There is currently no text in this page)

Simple English

[[File:|thumb|right|200px|The cyanide ion]] From the top:
1. Valence-bond structure
2. Space-filling model
3. Electrostatic potential surface
4. 'Carbon lone pair'

Cyanides are chemicals that contain the cyano-group. In that group a carbon atom has three bindings to a nitrogen atom. This group is present in many substances. Many of them are gases, but some are solids or liquids. Those substances that can release the compound CN are highly poisonous.

Certain bacteria, fungi and algae are able to produce cyanides. Cyanides are also found in certain foods or plants. In plants, the cyanides are usually bound to sugar molecules. The cyanides serve as a defense against being eaten by herbivores.

In popular culture, cyanides are said to be highly toxic. As stated above, there are many cyanides that really are, but many others that are not. Prussian blue is given as a treatment to poisoning with Thallium and Caesium, for example.

The poisons referred to are usually hydrogen cyanide (HCN), and the chemicals which are similar to it, like potassium cyanide (KCN), and sodium cyanide (NaCN). (Such substances are called derivatives of hydrogen cyanide). Organic compounds that contain the CN group are called nitriles. Many of them are not as toxic as the ones cited before. Some of them are even used to produce drugs.

Some people think that glucose (sugars) may be an antidote against cyanide poisoning. They think that sugar can bind the free cyano group. That way the some of the poison could be neutralized.

Got something to say? Make a comment.
Your name
Your email address