Cyanide

A cyanide is any chemical compoundthat contains the cyano group C≡N, with the carbonatomtriple-bondedto the nitrogenatom. Inorganiccyanides contain the highly toxic cyanide ion CN^?, and are the saltsof the acidhydrogen cyanide(HCN). Organiccyanides contain the cyano group single-bonded to another carbon atom, and are also known as nitriles. The cyano group is also known as the nitrile group.

Appearance and odour

Hydrogen cyanide is a colorless gas with a faint, bitter, almond-like odour. Nearly 40 percent of the population is unable to smell cyanide at all because they lack the necessary gene for smelling the odour. Sodium cyanide(NaCN) and potassium cyanide(KCN) are both white solids or powder with a bitter, almond-like odour in damp air.

Occurrence and uses

Cyanides can be produced by certain bacteria, fungi, and algae, and are found in a number of foods and plants. In plants, cyanides are usually bound to sugar molecules in the form of cyanogenic glycosidesand serve the plant as defense against herbivores. Cassavaroots (aka manioc), an important potato-like food grown in tropical countries, contain cyanogenic glycosides and must be processed prior to consumption (usually by extended boiling). Fruitsthat have a pit, such as cherriesand apricots, often contain either cyanides or cyanogenic glycosides in the pit. Appleseeds do as well. Bitter almonds, from which almond oil and flavouring is made, also contain a cyanogenic glycoside, amygdalin.

Hydrogen cyanide is contained in vehicle exhaust and in tobaccosmoke. Because the smoke of some burning plastics contains hydrogen cyanide, house fires often result in cyanide poisonings of the inhabitants. A deep bluepigment called Prussian blue, used in the making of blueprints, is iron(III) ferrocyanide (hence the name cyanide, from cyan, a shade of blue). It produces hydrogen cyanide when exposed to acids.

Goldand silvercyanides are among the very few solubleforms of these metals, and cyanides are thus used in mining, electroplating, metallurgy, jewelryand photographyfor chemical gilding, buffing, and extraction of gold. (See also below under Mining.)

Furthermore, cyanides and hydrogen cyanide are used in the production of chemicals including plastics, and as insecticideswhen fumigating ships. In the past they have also been used as rat poison.

In organic synthesis, cyanides are often used to lengthen the carbon chain:

RX + CN^? → RCN (Nucleophilic Substitution) followed by

1. RCN + H₃O⁺ → RCOOH(Hydrolysis), or
2. RCN + LiAlH₄→ RCH₂NH₂(under refluxin dry ether, followed by addition of H₃O⁺), or
3. RCN + NaBH₄→ RCOH.

In all the above cases, the number of carbon atoms of the main chain R is increased by one.

Potassium ferrocyanideis used to achieve a blue colour on cast bronze sculpturesduring 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.

Two cyanide ions can bond to each other via their carbon atoms, forming the gas cyanogen(NC-CN).

Mining

Cyanide salts are used in silverand goldmining, called the cyanide process. The high-grade ore is finely ground and 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 tonne). The precious-metal cationsbind to the cyanide anionsand form a soluble cyanide. The pregnant liquor is separated from the leftover dirt, which is discarded to a tailing pond or spent (the recoverable gold having been removed) heap. The metal is recovered from the pregnant solution with zincdustthat replaces the gold in solution or by absorption onto activated carbon. This process can result in environmental and health problems. Cyanide is highly reactive; it decomposes rapidly in sunlight. It can mobilize some heavy metals like mercury (if mercury is present). Gold can also be associated with arsenopyrite, which is similar to iron pyrite (fool's gold), with iron atoms replaced by arsenic.

Fishing

Cyanides are illegally used to capture live fish near coral reefsfor the aquariumand seafood markets. This fishing occurs mainly in the Philippines, Indonesiaand the Caribbeanto 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 so harvested has also resulted in cases of cyanide poisioning among local fishermen and their families.

Environmental organizations decry the practice, as do responsible 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.

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 is also possible, though rare.

Mechanism of toxicity

Cyanide ions bind to the iron atom of the enzymecytochrome c oxidasein the mitochondriaof cells. This deactivates the enzyme and breaks the electron transport chain, meaning that the cell can no longer use the oxygenwhich is available to it.

Tissues that mainly depend on aerobic respiration, such as the central nervous systemand the heart, are particularly affected.

Clinical symptoms

It is difficult to give dose figures in this section due to the rapid metabolismof 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 informationsection below may give some guidance.

Acute poisoning

Inhalation of high concentrations of hydrogen cyanide causes a convulsive comawith apneaand cardiac arrest, with death following in a matter of minutes.

At lower doses, loss of consciousness may be preceded by headaches, vertigoand 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.

Subacute poisoning

At doses insufficient to cause rapid loss of consciousness, the most widely reported symptoms are vertigo, inebriety, confusion and a feeling of tightness around the chest.

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

Chronic exposure

Exposure to lower levels of cyanide over a long period (e.g., after use of cassavaroots 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 glandfunction, 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.

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 odor in the breath may alert a doctor that a person was exposed to cyanide but not all people are able to smell HCN.

Treatment of poisoning and antidotes

The United Statesstandard cyanide antidotekit first uses a small inhaled dose of amyl nitritefollowed by intravenous sodium nitrite. This converts a portion of the hemoglobin's iron from ferrousiron to ferriciron, converting the hemoglobin into methemoglobin. Cyanide is more strongly drawn to methemoglobin than to the cytochrome oxidaseof the cells, effectively pulling the cyanide off the cells and onto the methemoglobin. Once bound with the cyanide, the methemoglobin becomes cyanmethemoglobin. Therapy with nitrites is not innocuous. The doses given to an adult can potentially cause a fatal methemoglobinemiain 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. The next part of the cyanide antidote kit is sodium thiosulfate, which is administered intravenously. The sodium thiosulfate and cyanmethemoglobin become thiocyanate, releasing the hemoglobin, and the thiocyanate is excreted by the kidneys.

Alternative methods of treating cyanide intoxication are used in other countries. For example, the method in France is to use hydroxycobalamin (a form of vitamin B₁₂), which combines with 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 contrasts with methemoglobin, which acts only within the vascular space as an antidote. Administration of sodium thiosulfateimproves 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 Germanyas a more rapid antidote than nitrites and with (reportedly) lower toxicity. It is used currently by the German military and by the civilian population. In humans, intravenous injection of 3 mg/kg of 4-DMAP will produce 35 percent methemoglobin levels within 1 minute. There are reports (de:4-Dimethylaminophenol), that 4-DMAP is part of the US Cyanokit, while it is not part of the GERM Cyanokit due to side effects (e. g. hemolysis).

Cobaltsaltshave 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 complexesare quite toxic, and there have been accidents reported in the UKwhere patients have been given dicobalt-EDTA by mistake based on a false diagnoses of cyanide poisoning.

The International Programme on Chemical Safetyissued a survey (IPCS/CEC Evaluation of Antidotes Series) which 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 sulphatein aqueous citric acid, and aqueous sodium carbonate) and amyl nitrite.

Britain's Health and Safety Executivehas recommended against the use of solutions A and B because of their limited shelf life, potential to cause iron poisoning, and limited use (effective only in cases of cyanide ingestion, whereas the main modes of poisoning are ingestion 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].

Glucose

There is evidence from animal experiments that coadministration of glucoseprotects 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 Rasputinto 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 cyanideor in the form of potassium cyanide(KCN) or sodium cyanide(NaCN).

Zyklon B, the poison gasused in Nazigas chambersduring the Holocaust, works by delivering hydrogen cyanide gas. Cyanide is also the compound used in U.S.gas chambersfor execution.

Cyanides were stockpiled in both the Sovietand the United Stateschemical weaponsarsenals in the 1950sand 1960s. 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 harmful gas itself would dissipate and allow unprotected access to the captured zone. However, as a military agent, cyanide was not considered very effective, since cyanide is lighter than air and requires a significant dose in order to incapacitate or kill.

Suicide

Cyanide salts are sometimes used as fast-acting suicide devices. When they reach the stomach acids, cyanide ions are released; therefore they work faster on an empty stomach. Famous cyanide salt suicides include:

• Erwin Rommel
• Adolf Hitler(likely, see article on Hitler's death)
• Joseph Goebbels
• Hermann Göring
• Heinrich Himmler
• Alan Turing
• Odilo Globocnik
• Eva Braun
• Martin Bormann

Some spy 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 being tortured or having information extracted from them.

Jonestown

Jonestown, Guyanawas the site of the largest mass sucide of all time, where 913 members of the Peoples Templedrank a cyanide-laced cup of Flavor Aidin 1978.

In fiction

Poisoning by cyanide also figures prominently in crime fiction, for example Agatha Christie's Sparkling Cyanide (also entitled Remembered Death); cyanide is the instrument of one murder in The Big Sleep by Raymond Chandler.

In Gabriel Garcia Marquez's Love in the Time of Cholera, one of the characters (a photographer) commits suicide using gold cyanide.

See also

• Category:Cyanides
• Victims of poisoning

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(CICAD61)
• IPCS/CEC Evaluation of antidotes for poisoning by cyanides
• National Pollutant Inventory - Cyanide compounds fact sheetda:Cyanid

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It uses material from the http://en.wikipedia.org/wiki/Cyanide Wikipedia article Cyanide.