Cyanide

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A cyanide is any chemical compound that contains the cyano group -C≡N, with the carbon atom triple-bonded to the nitrogen atom.

The CN group can be found in many kinds of compounds. Some are gases, others are solids or liquids. Some are salt-like, some covalent. Some are molecular, some ionic, and many are polymeric. Those that can release the cyanide ion CN⁻ are highly toxic.

Contents 1 Etymology 2 Appearance and odor 3 In nature 4 In chemistry 4.1 Coordination chemistry 4.2 Organic synthesis 5 Other occurrences and uses 5.1 Mining 5.2 Fishing 5.3 Fumigation 6 Toxicity 6.1 Absorption 6.2 Mechanism of toxicity 6.3 Clinical symptoms 6.3.1 Acute poisoning 6.3.2 Subacute poisoning 6.3.3 Chronic exposure 6.4 Diagnosis of poisoning 6.5 Treatment of poisoning and antidotes 6.5.1 Glucose 7 Poison use 7.1 Gas chambers 7.2 War 7.3 Suicide 7.3.1 Jonestown 7.4 Murder 7.5 Medical uses 8 In current events 9 In fiction 10 See also 11 References 12 Sources 13 External links

[edit] Etymology

The word "cyanide" was probably extracted from "ferrocyanide", which came from Latin ferrum = "iron" and Greek κυανεος = "blue", referring to the blue color of Prussian blue.^{[citation needed]}

[edit] Appearance and odor

Hydrogen cyanide (HCN) is a colorless gas with a faint bitter almond-like odor. Nearly everyone can smell hydrogen cyanide. This seems to be genetically determined in a complex fashion.^[1] 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

[edit] In nature

Cyanides can be produced by certain bacteria, fungi, and algae, and are found in a number of foods and plants. Cyanide is found, but in small amounts, in apple seeds and almonds.^[2] 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, contain cyanogenic glycosides^[3][4].

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. ^[5]

[edit] In chemistry

Cyanide is a versatile, highly toxic and invaluable anion that is widely encountered in all fields of chemistry.

[edit] 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.

[edit] Organic synthesis

Main article: Nitriles

Because of its high nucleophilicity, cyanide is readily introduced into organic molecules by displacement of the corresponding organic 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.

[edit] Other occurrences and uses

Hydrogen cyanide is a product of combustion, including the exhaust of internal combustion engines, tobacco smoke, and especially some plastics derived from acrylonitrile (because of the latter effect, house fires can result in poisonings of the inhabitants.)

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.

[edit] 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 solution (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.

[edit] 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.

[edit] 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.

[edit] 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 ¹³⁷Cs.

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).

[edit] 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.

[edit] 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.^[4] Interestingly, the Greater Bamboo Lemur is able to consume lethal doses of the Giant Bamboo shoots with no effect. The reason for its immunity is not yet understood.^[4]

[edit] 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.

[edit] 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.

[edit] Subacute poisoning

At doses insufficient to cause loss of consciousness, the symptoms can also include faintness, drowsiness, anxiety and excitement. Dizziness, nausea, vomiting and sweating are common.

The situation is complicated by the non-specific nature of the symptoms and by notoriety of the product. In some cases, such symptoms are psychosomatic, caused by anxiety at working with cyanides, and this is accentuated by the characteristic odour of hydrogen cyanide, detectable by healthy, undesensitised subjects at levels far below those which are believed to be toxic (odour threshold < 1 ppm). This is not to say that such symptoms should be taken lightly: if the patient is truly a victim of cyanide poisoning, their clinical state may deteriorate rapidly; while if the symptoms are psychosomatic, they will surely recur unless the anxieties about the safety procedures are addressed.

[edit] 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. These may result in weakness of the fingers and toes, difficulty walking, dimness of vision, deafness, and decreased thyroid gland function, but chemicals other than cyanide may contribute to these effects. Skin contact with cyanide can produce irritation and sores.

It is not known whether cyanides can directly cause birth defects in people. Birth defects were seen in rats that ate diets of cassava roots. Effects on the reproductive system were seen in rats and mice that drank water containing sodium cyanide.

[edit] Diagnosis of poisoning

There are medical tests to measure blood and urine levels of cyanide; however, small amounts of cyanide are not always detectable in blood and urine. Tissue levels of cyanide can be measured if cyanide poisoning is suspected, but cyanide is rapidly cleared from the body, so the tests must be done soon after the exposure. An almond-like odour in the breath may alert a doctor that a person was exposed to cyanide but not all people are able to smell HCN.

[edit] 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. 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. Methemoglobin cannot carry oxygen. The adult dose can cause a fatal methemoglobinemia in children or may cause profound hypotension. Treatment of children affected with cyanide intoxication must be individualized and is based upon their body weight and hemoglobin concentration.) Cyanide preferentially bonds to methemoglobin rather than the cytochrome oxidase, converting methemoglobin into cyanmethemoglobin. In the last step, the intravenous sodium thiosulfate reacts with the cyanmethemoglobin yielding 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 B_12a 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 nitrate due to storage/availability problems, risk of abuse, and lack of evidence of significant benefits, instead recommending Kelocyanor[2].

[edit] Glucose

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.

[edit] 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).

[edit] Gas chambers

Hydrogen cyanide gas was the agent used for mass murder in some gas chambers during the Holocaust. It was released from Zyklon B pellets, which were a commercial biocide product.

Cyanide is also the compound used in U.S. gas chambers for execution.

[edit] 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 need a significant dose to incapacitate or kill.

[edit] 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:

• Erwin Rommel
• Adolf Hitler (likely, see article on Hitler's death)
• Eva Braun
• Wallace Carothers
• Joseph Goebbels
• Hermann Göring
• Heinrich Himmler
• Alan Turing
• Odilo Globocnik
• Martin Bormann
• A North-Korean agent identified as Kim Sung Il, who along with a female accomplice in police custody in Bahrain bit into cyanide tablets hidden in cigarettes after having left a bomb onboard Korean Air Flight 858 which subsequently exploded over the Indian Ocean on November 29, 1987. The woman's life was saved by a quick-thinking police officer who knocked the cigarette away at the last second.
• Ramón Sampedro
• Gavrilo Princip attempted suicide, but failed
• Nedeljko Čabrinović attempted suicide, but failed
• Behzad Nabavi attempted suicide, but failed

Some espionage agents also carried glasses with cyanide in the frames. If they were caught by the enemy they could 'casually' chew the frame, releasing the cyanide, and die before having information extracted from them.^{[citation needed]} 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.

[edit] Jonestown

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

[edit] Murder

See:

• Goebbels children
• Tylenol scare
• Ronald Clark O'Bryan
• Grigori Rasputin

[edit] 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.

[edit] 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.^[6]

[edit] 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.

Australian author Nevil Shute's novel about life after nuclear war, On the Beach, gives us the scenario of the Australian goverment 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.

The protagonist in Metal Gear Solid 3 is given cyanide pills to use to fake his death if captured. A 'revival pill' is embedded into one of his back teeth to bring him back from 'death', but it is not known what chemicals are contained in this pill.

In the NCIS episode "Bloodbath" (Season 3, Episode 21), the forensic specialist, Abby, smells the distinctive almond-like smell of cyanide gas while examining evidence from a crime scene. She collapses while trying to escape her lab and is dragged to safety by another agent.

In the book "Hit Man: A Technical Manual for Independent Contractors", the use of cyanide to poison a mark is explained in detail.

In Kurt Vonnegut's Slaughterhouse Five, cyanide is the atmosphere of the fictional planet Tralfamadore. For this reason, the main character is confined in a geodesic dome.

In the Novel/Movie Battle Royale, girl #9; Yuko Sakaki was given Potassium cyanide as a weapon which she uses to try and kill protagonist Shuya Nanahara by poisoning his food. Unfortunately girl #16 Yuka Nakagawa eats the poisoned food and sets up the events of the infamous light house scene.

At the beginning of Love in the Time of Cholera by Gabriel Garcia Marquez, Jeremiah de Saint-Amour "had escaped the torments of memory with the aromatic fumes of gold cyanide."

[edit] See also

• Victims of poisoning

[edit] References

1. ^ Online Mendelian Inheritance in Man, Cyanide, inability to smell
2. ^ Agency for Toxic Substances and Disease Registry, ToxFaqs for Cyanide, Jul 2006.
3. ^ J. Vetter (2000). "Plant cyanogenic glycosides". Toxicon. 38: 11-36. DOI:10.1016/S0041-0101(99)00128-2. 
4. ^ ^{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. 
5. ^ 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. 
6. ^ Time Magazine, The Untold Story of al-Qaeda's Plot to Attack the Subway, 19 Jun 2006, accessed 20 Jan 2007.

[edit] 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)

[edit] 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