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==See also==
==See also==
* [[Victims of poisoning]]
* [[Victims of poisoning]]
* [[Cyanide and Happiness]]


==References==
==References==

Revision as of 00:15, 18 September 2007

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 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 geometry;
  • the tetracyanides, [M(CN)4]2− (M = Ni, Pd, Pt), which are square planar in 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 halide. 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), 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]−.

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

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 + 4KCN → 2K[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

"Cyanide" is a staple of crime fiction, often used synonymously with deadly poison. Many cyanide-containing compounds are indeed highly toxic, but many are not. Prussian blue, nominally Fe7(CN)18, a common pigment, is administered orally to counteract the effects of 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]

Many thousands of organic compounds contain the CN group. These compounds are called nitriles. Generally, nitriles do not display the toxicity of HCN, NaCN, and KCN. In fact, the nitrile functional group is an integral component of numerous pharmaceutical drugs including cimetidine (Tagamet), verapamil (Isoptin), and citalopram (celexa). The reason for their diminished toxicity is that nitriles do not release the CN− ion, which permanently binds to and inhibits cytochrome c oxidase, the specific basis of the lethality of cyanide (see below). Nitriles can be released from the burning of some plastics and may be a source of cyanide toxicity.

Absorption

The most usual route of absorption is by inhalation of hydrogen cyanide gas, which can be formed from alkaline cyanides and certain complex cyanides by the action of acid. Hydrogen cyanide poisoning is also common as a result of smoke inhalation after house fires.

Ingestion is equally dangerous, although this route of absorption is usually deliberate (suicidal or criminal).

Absorption through the skin as an aqueous solution is low. Potassium or sodium cyanide can pass through the skin easily as a DMSO solution, though this is rare.

Mechanism of toxicity

Cyanide is an irreversible enzyme inhibitor. Cyanide ions bind to the iron atom of the enzyme cytochrome c oxidase (also known as aa3) in the fourth complex in the mitochondrial membrane in the mitochondria of cells. This denatures the enzyme, and the final transport of electrons from cytochrome c oxidase to oxygen cannot be completed. 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.

Plants contain an alternative pathway for respiration in their mitochondria. The alternate oxidase is not as efficient as the normal pathway, but immune to cyanide. As a result, plants are insensitive to concentrations of cyanide that are lethal to animals, and a few species (e.g. the Giant Bamboo in its shoots) are known to contain cyanides.[5] Interestingly, the Golden Bamboo Lemur is able to consume Giant Bamboo shoots containing many times the lethal dose of cyanide for humans and most other animals, with no ill effects. The reason for its immunity is not yet understood.[5]

Clinical symptoms

It is difficult to give dose figures in this section due to the rapid metabolism of cyanide in the human body. Animal studies are of little help, as different species have widely different sensitivities to cyanide: it is quite possible that there is also a considerable range of sensitivity among human individuals. The Regulatory information section below may give some guidance.

Acute poisoning

Inhalation of high concentrations of cyanide causes a coma with seizures, apnea and cardiac arrest, with death following in a matter of minutes.

At lower doses, loss of consciousness may be preceded by general weakness, giddiness, headaches, vertigo, confusion, and perceived difficulty in breathing. At the first stages of unconsciousness, breathing is often sufficient or even rapid, although the state of the victim progresses towards a deep coma, sometimes accompanied by pulmonary edema, and finally cardiac arrest. Skin colour goes pink from high blood oxygen saturation.

Chronic exposure

Exposure to lower levels of cyanide over a long period (e.g., after use of cassava roots as a primary food source in tropical Africa) results in increased blood cyanide levels, which can result in weakness and a variety of symptoms, including permanent paralysis.

Treatment of poisoning and antidotes

The United States standard cyanide antidote kit first uses a small inhaled dose of amyl nitrite, followed by intravenous sodium nitrite, followed by intravenous sodium thiosulfate.[citation needed] The nitrites oxidize some of the hemoglobin's iron from the ferrous state to the ferric state, converting the hemoglobin into methemoglobin. (Treatment with nitrites is not innocuous as methemoglobin cannot carry oxygen). Cyanide preferentially bonds to methemoglobin rather than the cytochrome oxidase, converting methemoglobin into cyanmethemoglobin. In the last step, the intravenous sodium thiosulfate converts the cyanmethemoglobin to thiocyanate, sulfite, and hemoglobin. The thiocyanate is excreted.

Alternative methods of treating cyanide intoxication are used in other countries. For example, in France hydroxycobalamin (a form of vitamin B12) is used to bind cyanide to form the harmless vitamin B12a cyanocobalamin. Cyanocobalamin is eliminated through the urine. Hydroxycobalamin works both within the intravascular space and within the cells to combat cyanide intoxication. This versatility contrasts with methemoglobin, which acts only within the vascular space as an antidote. Administration of sodium thiosulfate improves the ability of the hydroxycobalamin to detoxify cyanide poisoning. This treatment is considered so effective and innocuous that it is administered routinely in Paris to victims of smoke inhalation to detoxify any associated cyanide intoxication. However it is relatively expensive and not universally available.

4-Dimethylaminophenol (4-DMAP) has been proposed in Germany as a more rapid antidote than nitrites with (reportedly) lower toxicity. 4-DMAP is used currently by the German military and by the civilian population. In humans, intravenous injection of 3 mg/kg of 4-DMAP produces 35 percent methemoglobin levels within 1 minute. Reportedly, 4-DMAP is part of the US Cyanokit, while it is not part of the GERM Cyanokit due to side effects (e. g. hemolysis).

Cobalt salts have also been demonstrated as effective in binding cyanide. One current cobalt-based antidote available in Europe is dicobalt-EDTA, sold as Kelocyanor®. This agent chelates cyanide as the cobalticyanide. This drug provides an antidote effect more quickly than formation of methemoglobin, but a clear superiority to methemoglobin formation has not been demonstrated. Cobalt complexes are quite toxic, and there have been accidents reported in the UK where patients have been given dicobalt-EDTA by mistake based on a false diagnoses of cyanide poisoning.

The International Programme on Chemical Safety issued a survey (IPCS/CEC Evaluation of Antidotes Series) that lists the following antidotal agents and their effects: Oxygen, sodium thiosulfate, amyl nitrite, sodium nitrite, 4-dimethylaminophenol, hydroxocobalamin, and dicobalt edetate ('Kelocyanor'), as well as several others[1]. Other commonly-recommended antidotes are 'solutions A and B' (a solution of ferrous sulphate in aqueous citric acid, and aqueous sodium carbonate) and amyl nitrite.

Britain's Health and Safety Executive(HSE) has recommended against the use of solutions A and B because of their limited shelf life, potential to cause iron poisoning, and limited applicability (effective only in cases of cyanide ingestion, whereas the main modes of poisoning are inhalation and skin contact). The HSE has also questioned the usefulness of amyl nitrite due to storage/availability problems, risk of abuse, and lack of evidence of significant benefits, instead recommending Kelocyanor[2].

Evidence from animal experiments suggests that coadministration of glucose protects against cobalt toxicity associated with the antidote agent dicobalt edetate. For this reason, glucose is often administered alongside this agent (e.g. in the formulation 'Kelocyanor').

It has also been anecdotally suggested that glucose is itself an effective counteragent to cyanide, reacting with it to form less toxic compounds that can be eliminated by the body. One theory on the apparent immunity of Grigory Rasputin to cyanide was that his killers put the poison in sweet pastries and madeira wine, both of which are rich in sugar; thus, Rasputin would have been administered the poison together with massive quantities of antidote. One study found a reduction in cyanide toxicity in mice when the cyanide was first mixed with glucose[3]. However, as yet glucose on its own is not an officially acknowledged antidote to cyanide poisoning.

Poison use

The cyanide ion, if used as poison, is generally delivered in the form of gaseous hydrogen cyanide or in the form of potassium cyanide (KCN) or sodium cyanide (NaCN).

Gas chambers

Hydrogen cyanide gas was the agent used during the National Socialist (Nazi) regime in Germany for mass murder in some gas chambers during the Holocaust. It was released from Zyklon B pellets, which were a commercial biocide product. It was also used in US execution chambers, generated by reaction between potassium cyanide dropped into a compartment containing sulfuric acid directly below the chair in the chamber.

War

Cyanides were stockpiled in both the Soviet and the United States chemical weapons arsenals in the 1950s and 1960s.[citation needed] During the Cold War, the Soviet Union was thought to be planning to use hydrogen cyanide as a "blitzkrieg" weapon to clear a path through the opposing front line, knowing that the hydrogen cyanide would dissipate and allow unprotected access to the captured zone.[citation needed] However, as a military agent, hydrogen cyanide was not considered very effective, since it is lighter than air and needs a significant dose to incapacitate or kill.

Suicide

Cyanide salts are sometimes used as fast-acting suicide devices. Cyanide is reputed to work faster on an empty stomach, possibly because the anion is protonated by stomach acids to give HCN. Famous cyanide salt suicides include:

Members of the Liberation Tigers of Tamil Eelam which operate in north-eastern Sri Lanka are probably the most reported to use capsules made out of cyanide compound/compounds, where each member of the militia wears a capsule round their neck, which is used to commit suicide when they are about to be captured by the security forces of Sri Lanka.

Jonestown, Guyana was the site of a large mass suicide/murder, where 913 members of the Peoples Temple drank potassium cyanide-laced Flavor Aid in 1978.

Murder

See:

In current events

Terrorists planned on releasing cyanide gas into the New York City Subway system shortly after the September 11th attacks. The attack was reportedly called off because there would not be enough casualties.[7]

In fiction

Poisoning by cyanide figures prominently in crime fiction, for example Agatha Christie's Sparkling Cyanide (also entitled Remembered Death) and And Then There Were None. Cyanide is also the instrument of murder in The Big Sleep by Raymond Chandler and Roald Dahl's short story "The Landlady". In the Joseph Kesselring play "Arsenic and Old Lace," two old ladies mix wine with arsenic, cyanide and strychnine to use to kill old men. In the book "Hit Man: A Technical Manual for Independent Contractors", the use of cyanide to poison a mark is explained in detail.

Though not as famous as his Joker toxin or his electric joy-buzzers, the Joker from Batman comics is also known to use cyanide pies as one of his "comedic" weapons.

Australian author Nevil Shute's novel about life after nuclear war, On the Beach, gives the scenario of the Australian government giving survivors free cyanide tablets to commit suicide rather than face death from radiation poisoning.

In the James Bond movies and novels, 00 agents are issued cyanide capsules for use in the event of capture by the enemy. James Bond is described as having thrown his away. Assassins in the films have also used cyanide as a quick suicide method such as Mr. Jones in Dr. No, and in The Spy Who Loved Me, British and American nuclear submarines are threatened with the injection of Cyanide gas to force their crews to surrender to the villain's henchmen.

In the show 24 there are many instances where terrorists will bite a cyanide capsule to avoid harsh interrogation.

See also

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. ^ a b c 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.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  7. ^ Time Magazine, The Untold Story of al-Qaeda's Plot to Attack the Subway, 19 Jun 2006, accessed 20 Jan 2007.

Sources

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