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Cyanide (CN-) is a highly toxic ion found in compounds called cyanides. It has a net charge of -1. The carbon atom is triple bonded with the nitrogen atom.

The name "cyanide" also commonly refers to hydrogen cyanide (HCN), or to the various common cyanide salts, such as sodium cyanide (NaCN) or potassium cyanide (KCN). Cyanide can be produced by certain bacteria, fungi, and algae, and it is found in a number of foods and plants. In the body, cyanide combines with a chemical to form vitamin B12. Cyanide occurs naturally in cassava roots, which are potato-like tubers of cassava plants grown in tropical countries; these must be processed prior to consumption.

Fruits, such as cherries, which have a pit often contain significant quantities of cyanide ion in the pit, which can be liberated and concentrated during processing. Bitter almonds from which almond oil and flavoring is made also contain cyanide. A deep blue pigment called Prussian Blue[?], used in the making of blueprints, contains cyanide.

Hydrogen cyanide is a colorless gas with a faint, bitter, almond-like odor. Sodium cyanide and potassium cyanide are both white solids with a bitter, almond-like odor in damp air. Cyanides and hydrogen cyanide are used in electroplating, metallurgy, production of chemicals, photographic development, making plastics, fumigating ships, and some mining processes.

Use as a poison

Cyanide ion kills all aerobic organisms by shutting down the electron transport chain in the inner membrane of the mitochondrion: it binds stronger to the Fe+3 in cytochrome a3 than oxygen does, preventing this cytochrome from combining electrons with oxygen. Contrary to popular belief, cyanide does not bind well to ferrous hemoproteins, such as hemoglobin. One of the therapies for cyanide poisoning is to convert part of the hemoglobin of the blood from ferrous hemoglobin to ferric; this creates a pool of binding potential that can divert cyanide from the cytochromes it poisons.

The cyanide ion, if used as poison, is normally delivered in the form of gaseous hydrogen cyanide.

Zyklon B, the pesticide used in German gas chambers during the Holocaust, works by delivering hydrogen cyanide gas. Hydrogen cyanide is also the compound used in US execution gas chambers.

The cyanide salts are fast acting "suicide pills". When they reach the stomach acids, hydrogen cyanide is released; therefore they work faster on an empty stomach. Famous cyanide salt suicides include:

Poisoning by cyanide also figures prominently in crime fiction, for example Agatha Christie's Sparkling Cyanide.

Cyanide was stockpiled in both the Soviet and the United States chemical weapons arsenals in the 1950s and 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 evaporate and allow unprotected access to the captured zone.

Health effects

In large amounts, cyanide is very harmful to people. Exposure to high levels of cyanide in the air for a short time harms the brain and heart, and may cause coma and death.

Exposure to lower levels of cyanide for a long time may result in breathing difficulties, heart pains, vomiting, blood changes, headaches, and enlargement of the thyroid gland.

People who eat large amounts of cyanide may have symptoms including deep breathing and shortness of breath, convulsions, and loss of consciousness, and may die. Use of cassava roots as a primary food source in tropical Africa has led to high blood cyanide levels.

People with high blood cyanide levels have also shown harmful effects such as weakness of the fingers and toes, difficulty walking, dimness of vision, deafness, and decreased thyroid gland function, but chemicals other than cyanide may have contributed to these effects. Skin contact with cyanide can produce irritation and sores.

It is not known whether cyanide 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

There are medical tests to measure blood and urine levels of cyanide; however, small amounts of cyanide are 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.

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