Hydrogen cyanide
Hydrogen cyanide (HCN) is a highly toxic chemical compound formed from the bonding of hydrogen, carbon, and nitrogen atoms. It appears as a colorless gas at higher temperatures and can take on a pale blue hue in liquid form, with a distinctive bitter odor reminiscent of almonds. Known for its lethal potential, hydrogen cyanide can be fatal within minutes at high concentrations, as it interferes with the body's ability to utilize oxygen, leading to cellular energy failure. Historically, hydrogen cyanide was used in the gas chambers during World War II and is associated with various chemical warfare incidents.
Despite its dangers, hydrogen cyanide serves important industrial purposes, including its use in mining for precious metals and as a precursor in the production of plastics and dyes. It is also found in low concentrations in everyday items like cigarette smoke and certain edible plants, such as almonds and cassava, which can be toxic if not prepared properly. Additionally, hydrogen cyanide has been detected in extraterrestrial settings, including gas clouds in interstellar space and the atmospheres of moons and planets, showcasing its presence beyond Earth. Understanding hydrogen cyanide's properties and risks is crucial for safety and industrial applications.
On this Page
Subject Terms
Hydrogen cyanide
Hydrogen cyanide is a highly toxic chemical compound produced by the bonding of single atoms of hydrogen, carbon, and nitrogen. Its chemical formula is written as HCN. Hydrogen cyanide exists as a liquid at temperatures below 78 degrees Fahrenheit (25.6 degrees Celsius) and as a gas at higher temperatures. It becomes a solid below 8 degrees Fahrenheit (-13.4 degrees Celsius). Hydrogen cyanide is colorless in its gas form and may have a pale blue tint as a liquid. In high concentrations, the substance can be deadly to humans in a short time. During World War II (1939–1945), hydrogen cyanide was used in the gas chambers of the Nazi death camps. Despite its toxicity, the compound is used for a variety of industrial purposes, including mining, fumigation, and making plastics and dyes. It is also found in cigarette smoke, in the atmospheres of celestial bodies, and in some edible plants.
Background
Swedish scientist Carl Wilhelm Scheele discovered hydrogen cyanide in 1782. Scheele was experimenting with a chemical dye named Prussian blue. It was named because it was used to give the blue coats of the Prussian army their color. The chemical formula for the dye is Fe7(CN)18 because it contains seven atoms of iron (Fe) and eighteen atoms each of carbon and nitrogen. The carbon and nitrogen atoms are bonded together to form a chemical compound known as a cyanide. Cyanides were named from the Greek word kyanos, meaning "dark blue," and –ide, a common suffix used in chemistry. By combining the Prussian blue dye with the substance mercury(II) oxide and heating the mixture, Scheele was eventually able to isolate hydrogen cyanide. Hydrogen cyanide is sometimes referred to as prussic acid, formonitrile, and hydrocyanic acid.
Overview
Hydrogen cyanide is formed by the bonding of hydrogen, carbon, and nitrogen atoms. The carbon and nitrogen atoms are attached to each other by a strong chemical bond known as a triple bond—a bond in which the atoms share six electrons rather than the usual two. The hydrogen atom is connected by a weaker bond. The substance emits a bitter odor similar to almonds. Its odor has also been described as smelling like musty sneakers.
In high doses, hydrogen cyanide can be lethal in a matter of minutes. The National Institute for Occupational Safety and Health (NIOSH) lists acceptable levels of exposure to hydrogen cyanide in air at 4.7 parts per million and exposure through the skin at 5 milligrams per cubic meter. Exposure to the substance at 100 to 300 parts per million can prove fatal in ten to sixty minutes. In the body, hydrogen cyanide bonds with iron atoms inside cells. This action prevents the enzyme cytochrome C oxidase from performing its role in converting oxygen to the energy the body needs. With their source of energy blocked, the heart and central nervous system begin to shut down, eventually resulting in death. Several antidotes and treatments for hydrogen cyanide poising are available, but they need to be administered quickly.
The French attempted to use hydrogen cyanide as a chemical weapon in World War I (1914–1918), but the gas proved too unstable and easily dispersed into the air to be effective. In the 1920s, hydrogen cyanide was used as the active ingredient in an insecticide called Zyklon B. During World War II, the Germans used Zyklon B gas in the mass murder of Jews during the Holocaust. Hydrogen cyanide is also believed to have been used as a weapon by Iraq in its war with Iran and against the Kurdish people in the 1980s. The substance is listed as a chemical warfare agent by the Organisation for the Prohibition of Chemical Weapons.
The iron-bonding abilities of hydrogen cyanide that make it deadly also make it useful for some industrial purposes. The substance can be used in gold and silver mining to separate the precious metals from the ore. Hydrogen cyanide is also used as a starting point in the chemical synthesis of certain products, such as nylon, plastics, and dyes. Chemical synthesis involves a coordinated series of chemical reactions to change the structure of a chemical compound to create a new one.
Hydrogen cyanide is present in the exhaust given off by automobiles and in cigarette smoke. In both cases, however, the amounts are too small to be deadly by themselves. Some insects emit or spray hydrogen cyanide as a defense mechanism to ward off predators. Small amounts of hydrogen cyanide are also found in almonds, peach pits, and apple seeds. The cassava, a root vegetable used as a primary food source in many African and South American nations, contains a relatively high concentration of hydrogen cyanide. Some varieties have enough to be fatal. The cassava must be properly prepared and cooked to eliminate the danger of poisoning.
Astronomers have found evidence of hydrogen cyanide in gas clouds floating in interstellar space and in the atmospheres of stars, planets, and moons. In the early twentieth century, the detection of a gas similar to hydrogen cyanide in the tail of Halley's Comet caused some panic on Earth when it was announced the planet would pass through the tail. The concerns were unfounded, as the amount of gas was too low to pose any danger. In 2012, the spacecraft Cassini discovered a 386,000-square-mile (1-million-square-kilometer) cloud of hydrogen cyanide in the upper atmosphere of Titan, Saturn's largest moon. The cloud is made of tiny particles of frozen hydrogen cyanide. In 2016, astronomers detected the substance in the atmosphere of 55 Cancri e, a planet orbiting a star about forty light years from Earth.
Bibliography
Choi, Charles Q. "Huge Cloud on Saturn's Moon Titan Is Made of Toxic Cyanide." Space.com, 1 Oct. 2014, www.space.com/27310-cyanide-cloud-saturn-moon-titan.html. Accessed 28 Feb. 2018.
"Environmental & Health Effects." International Cyanide Management Institute, www.cyanidecode.org/cyanide-facts/environmental-health-effects. Accessed 28 Feb. 2018.
"Hydrogen Cyanide." Chemistry World, 21 Dec. 2011, www.chemistryworld.com/podcasts/hydrogen-cyanide/3005803.article. Accessed 28 Feb. 2018.
"Hydrogen Cyanide." Organisation for the Prohibition of Chemical Weapons, www.opcw.org/about-chemical-weapons/types-of-chemical-agent/blood-agents/hydrogen-cyanide. Accessed 28 Feb. 2018.
"Hydrogen Cyanide." PubChem, pubchem.ncbi.nlm.nih.gov/compound/hydrogen‗cyanide#section=Top. Accessed 28 Feb. 2018.
"Hydrogen Cyanide (AC) : Systemic Agent." Centers for Disease Control and Prevention, 9 Nov. 2017, www.cdc.gov/niosh/ershdb/emergencyresponsecard‗29750038.html. Accessed 28 Feb. 2018.
Krämer, Katrina. "Tiny Mite Uses Hydrogen Cyanide to Fight Predators." Chemistry World, www.chemistryworld.com/news/tiny-mite-uses-hydrogen-cyanide-to-fight-predators/3006980.article. Accessed 28 Feb. 2018.
Lennartson, Anders. "Publication 35. Isolation of Hydrocyanic Acid from Prussian Blue." The Chemical Works of Carl Wilhelm Scheele. Springer, 2017, pp. 75–78.
Martin, Terry. "Facts about Hydrogen Cyanide in Cigarette Smoke." Very Well, 25 Dec. 2017, www.verywellmind.com/hydrogen-cyanide-in-cigarette-smoke-2824423. Accessed 28 Feb. 2018.