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Hydrogen cyanide, sometimes called prussic acid, is a
chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemical bonds. A homonuclear molecule, m ...
with the
chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, commas and ...
HCN. It is a
color Color (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American Engli ...

color
less, extremely
poison In biology, poisons are Chemical substance, substances that can cause death, injury or harm to organs, Tissue (biology), tissues, Cell (biology), cells, and DNA usually by chemical reactions or other activity (chemistry), activity on the molecul ...

poison
ous, and
flammable , Germany ) , image_map = , map_caption = , map_width = 250px , capital = Berlin , coordinates = , largest_city = capital , languages_type = Official language , languages = German language, German , demonym = Germans, German , g ...
liquid that
boils A boil, also called a furuncle, is a deep folliculitis Folliculitis is the infection and inflammation of one or more hair follicle The hair follicle is an organ found in mammalian skin. It resides in the dermal layer of the skin and is made ...
slightly above
room temperature Colloquially, room temperature is the range of air temperature Temperature is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy, present in all matter, which is the source of the occurrence of heat ...
, at . HCN is produced on an industrial scale and is a highly valued precursor to many chemical compounds ranging from
polymers A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Repeat unit, repeating subunits. Due to thei ...

polymers
to pharmaceuticals. Large-scale applications are for the production of
potassium cyanide Potassium cyanide is a compound with the formula In , a formula is a concise way of expressing information symbolically, as in a mathematical formula or a . The informal use of the term ''formula'' in science refers to the . The plural of ...
and
adiponitrile Adiponitrile is the organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, ca ...

adiponitrile
, used in mining and plastics, respectively.


Structure and general properties

Hydrogen cyanide is a linear molecule, with a
triple bond A triple bond in chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they un ...

triple bond
between
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
and
nitrogen Nitrogen is the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

nitrogen
. The
tautomer Tautomers () are structural isomer In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, ...

tautomer
of HCN is HNC,
hydrogen isocyanide Hydrogen isocyanide is a chemical with the molecular formula HNC. It is a minor tautomer of hydrogen cyanide (HCN). Its importance in the field of astrochemistry is linked to its ubiquity in the interstellar medium. Nomenclature Both ''hydr ...
. Hydrogen cyanide is weakly
acidic An acid is a molecule A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In phys ...
with a p''K''a of 9.2. It partially ionizes in water solution to give the
cyanide A cyanide is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by che ...

cyanide
anion, CN. A solution of hydrogen cyanide in
water Water (chemical formula H2O) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known li ...
, represented as HCN, is called ''hydrocyanic acid''. The
salt Salt is a mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure fo ...
s of the cyanide anion are known as
cyanide A cyanide is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by che ...

cyanide
s. HCN has a faint
bitter almond The almond (''Prunus dulcis'', syn. ''Prunus amygdalus'') is a species of tree native to Iran Iran ( fa, ایران ), also called Persia and officially the Islamic Republic of Iran ( fa, جمهوری اسلامی ایران ), is a ...
-like
odor An odor (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of variety (linguistics), varieties of the English language native to the United States. Cur ...
that some people are unable to
detect
detect
owing to a recessive
gene In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mecha ...

gene
tic
trait Trait may refer to: * Phenotypic trait in biology, which involve genes and characteristics of organisms * Trait (computer programming), a model for structuring object-oriented programs (a template class in the C++ programming language) * Trait the ...
. The volatile compound has been used as inhalation
rodenticide Rodenticides are chemical A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical ...
and human poison, as well as for killing whales. Cyanide ions interfere with iron-containing respiratory enzymes.


History of discovery

Hydrogen cyanide was first isolated from a blue pigment (
Prussian blue Prussian blue (also known as Berlin blue or, in painting Painting is the practice of applying paint Paint is any pigmented liquid, liquefiable, or solid mastic composition that, after application to a substrate in a thin layer, ...

Prussian blue
) which had been known since 1706, but whose structure was unknown. It is now known to be a
coordination polymer A coordination polymer is an inorganic polymer, inorganic or organometallic chemistry, organometallic polymer structure containing metal cation centers linked by ligands. More formally a coordination polymer is a coordination compound with repeatin ...
with a complex structure and an empirical formula of hydrated ferric
ferrocyanide Ferrocyanide is the name of the anion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All e ...

ferrocyanide
. In 1752, the French chemist
Pierre Macquer Pierre-Joseph Macquer (9 October 1718, Paris – 15 February 1784, Paris) was an influential French people, French chemist. He is known for his ''Dictionnaire de chymie'' (1766). He was also involved in practical applications, to medicine and indus ...
made the important step of showing that Prussian blue could be converted to an
iron oxide Iron oxides are chemical compounds composed of iron and oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, ...

iron oxide
plus a volatile component and that these could be used to reconstitute it. The new component was what is now known as hydrogen cyanide. Following Macquer's lead, it was first prepared from Prussian blue by the Swedish chemist
Carl Wilhelm Scheele Carl Wilhelm Scheele (, ; 9 December 1742 – 21 May 1786) was a German and Swedish Pomerania Swedish Pomerania ( sv, Svenska Pommern; german: Schwedisch-Pommern) was a Dominion The word Dominion was used from 1907 to 1948 to refer to one of ...

Carl Wilhelm Scheele
in 1782, and was eventually given the German name ''Blausäure'' (''lit''. "Blue acid") because of its acidic nature in water and its derivation from Prussian blue. In English, it became known popularly as ''prussic acid.'' In 1787, the French chemist
Claude Louis Berthollet Claude Louis Berthollet statue in Annecy, France Claude Louis Berthollet (9 December 1748 – 6 November 1822) was a Savoy Savoy (; frp, Savouè ; french: Savoie ; it, Savoia ; pms, Savòja ; ) is a cultural-historical region in the W ...
showed that prussic acid did not contain oxygen, an important contribution to acid theory, which had hitherto postulated that acids must contain oxygen (hence the name of
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
itself, which is derived from Greek elements that mean "acid-former" and are likewise
calque In linguistics Linguistics is the scientific study of language, meaning that it is a comprehensive, systematic, objective, and precise study of language. Linguistics encompasses the analysis of every aspect of language, as well as the me ...

calque
d into German as ''Sauerstoff''). In 1811,
Joseph Louis Gay-Lussac Joseph Louis Gay-Lussac (, , ; 6 December 1778  – 9 May 1850) was a French chemist and physicist. He is known mostly for his discovery that water is made of two parts hydrogen and one part oxygen (with Alexander von Humboldt Friedric ...

Joseph Louis Gay-Lussac
prepared pure, liquified hydrogen cyanide. In 1815, Gay-Lussac deduced Prussic acid's chemical formula. The radical ''cyanide'' in hydrogen cyanide was given its name from
cyan Cyan () is the color between green Green is the between and on the . It is evoked by light which has a of roughly 495570 . In systems, used in painting and color printing, it is created by a combination of yellow and ; in the , u ...

cyan
, not only an English word for a shade of blue but the Greek word for blue ( grc, κύανος), again owing to its derivation from Prussian blue.


Production and synthesis

Hydrogen cyanide forms in at least limited amounts from many combinations of hydrogen, carbon, and
ammonia Ammonia is a chemical compound, compound of nitrogen and hydrogen with the chemical formula, formula NH3. A Binary compounds of hydrogen, stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct ch ...

ammonia
. Hydrogen cyanide is currently produced in great quantities by several processes, as well as being a recovered waste product from the manufacture of
acrylonitrile Acrylonitrile is an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, a ...
. In 2006 between 500 million and 1 billion pounds (between 230,000 and 450,000 t) were produced in the US. The most important process is the Andrussow oxidation invented by
Leonid Andrussow Leonid Andrussow (28 November 1896 in Riga Riga (; lv, Rīga , liv, Rīgõ) is the capital of Latvia and is home to 627,487 inhabitants (2020), which is a third of Latvia's population. Being significantly larger than List of cities and tow ...
at
IG Farben Interessengemeinschaft Farbenindustrie AG (), commonly known as IG Farben (German for "IG Colors"), was a German chemical and pharmaceutical conglomerate Conglomerate or conglomeration may refer to: * Conglomerate (company) * Conglomerate (geo ...
in which
methane Methane (, ) is a chemical compound with the chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes a ...
and
ammonia Ammonia is a chemical compound, compound of nitrogen and hydrogen with the chemical formula, formula NH3. A Binary compounds of hydrogen, stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct ch ...

ammonia
react in the presence of
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
at about over a
platinum Platinum is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical el ...

platinum
catalyst: :2 CH4 + 2 NH3 + 3 O2 → 2 HCN + 6 H2O The energy needed for the reaction is provided by the partial oxidation of methane and ammonia. Of lesser importance is the
Degussa Evonik Industries AG is a stock-listed German speciality chemicals company headquartered in Essen Essen (; Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin wa ...
process (
BMA processThe BMA process or Degussa process is a chemical process developed by the German chemical company Degussa Evonik Industries AG is a stock-listed German speciality chemicals company headquartered in Essen Essen (; Latin Latin (, or , ) is a cla ...
) in which no oxygen is added and the energy must be transferred indirectly through the reactor wall: :CH4 + NH3 → HCN + 3H2 This reaction is akin to
steam reforming Steam reforming or steam methane reforming is a method for producing syngas (hydrogen and carbon monoxide) by reaction of hydrocarbons with water. Commonly natural gas is the feedstock. The main purpose of this technology is hydrogen production. The ...
, the reaction of
methane Methane (, ) is a chemical compound with the chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes a ...
and water to give
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom. It is the simplest molecule of the oxocarbon family. In ...

carbon monoxide
and
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

hydrogen
. In the Shawinigan Process,
hydrocarbons In organic chemistry Organic chemistry is a branch of chemistry that studies the structure, properties and reactions of organic compounds, which contain carbon in covalent bonding.Clayden, J.; Greeves, N. and Warren, S. (2012) ''Organic Chemistry ...
, e.g.
propane Propane () is a three-carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's ...

propane
, are reacted with ammonia. In the laboratory, small amounts of HCN are produced by the addition of acids to cyanide salts of
alkali metals The alkali metals consist of the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a ...
: :H+ + NaCN → HCN + Na+ This reaction is sometimes the basis of accidental poisonings because the acid converts a nonvolatile cyanide salt into the gaseous HCN.


Historical methods of production

The large demand for cyanides for mining operations in the 1890s was met by George Thomas Beilby, who patented a method to produce hydrogen cyanide by passing
ammonia Ammonia is a chemical compound, compound of nitrogen and hydrogen with the chemical formula, formula NH3. A Binary compounds of hydrogen, stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct ch ...

ammonia
over glowing
coal Coal is a combustible , Germany ) , image_map = , map_caption = , map_width = 250px , capital = Berlin , coordinates = , largest_city = capital , languages_type = Official language , languages = German language, German , ...

coal
in 1892. This method was used until
Hamilton Castner Hamilton Young Castner (September 11, 1858 – October 11, 1899) was an American industrial chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a scientist A scientist is a perso ...
in 1894 developed a synthesis starting from coal, ammonia, and
sodium Sodium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical eleme ...

sodium
yielding
sodium cyanide Sodium cyanide is a poisonous compound with the formula In science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowledge in the ...

sodium cyanide
, which reacts with acid to form gaseous HCN.


Applications

HCN is the precursor to
sodium cyanide Sodium cyanide is a poisonous compound with the formula In science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowledge in the ...

sodium cyanide
and
potassium cyanide Potassium cyanide is a compound with the formula In , a formula is a concise way of expressing information symbolically, as in a mathematical formula or a . The informal use of the term ''formula'' in science refers to the . The plural of ...
, which are used mainly in
gold Gold is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elemen ...

gold
and
silver Silver is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical ele ...

silver
mining and for the electroplating of those metals. Via the intermediacy of
cyanohydrin A cyanohydrin or hydroxynitrile is a functional group found in organic compounds in which a cyano and a hydroxy group are attached to the same carbon atom. The general formula is R2C(OH)CN, where R is H, alkyl, or aryl. Cyanohydrins are industria ...

cyanohydrin
s, a variety of useful organic compounds are prepared from HCN including the
monomer In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in th ...

monomer
methyl methacrylate Methyl methacrylate (MMA) is an organic compound with the chemical formula, formula CH2=C(CH3)COOCH3. This colorless liquid, the methyl ester of methacrylic acid (MAA), is a monomer produced on a large scale for the production of poly(methyl meth ...

methyl methacrylate
, from
acetone Acetone, or propanone, is an organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, ...

acetone
, the
amino acid Amino acids are organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, a ...

amino acid
methionine Methionine (symbol Met or M) () is an essential amino acid An essential amino acid, or indispensable amino acid, is an amino acid that cannot be synthesized from scratch by the organism fast enough to supply its demand, and must therefore come ...

methionine
, via the , and the chelating agents
EDTA Ethylenediaminetetraacetic acid (EDTA) is an aminopolycarboxylic acid left, 120px, a metal complex with the EDTA anion file:Asparaginsäure - Aspartic acid.svg, 120px, Aspartic acid is an aminodicarboxylic acid and precursor to other ligands. An ...

EDTA
and NTA. Via the
hydrocyanation Hydrocyanation is the addition of hydrogen, H+ and cyanide, –CN to Substrate (chemistry), substrate. Usually the substrate is an alkene and the product is a nitrile. Hydrocyanation of unactivated alkenes Industrially, hydrocyanation is comm ...

hydrocyanation
process, HCN is added to
butadiene 1,3-Butadiene (/ˌbjuːtəˈdʌɪiːn/) is the organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds c ...

butadiene
to give
adiponitrile Adiponitrile is the organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, ca ...

adiponitrile
, a precursor to
Nylon-6,6 Nylon 66 (loosely written nylon 6-6, nylon 6/6 or nylon 6,6) is a type of polyamide or nylon Nylon is a generic designation for a family of synthetic polymers composed of polyamides (polymer, repeating units linked by amide links).The polya ...

Nylon-6,6
. HCN is used globally as a fumigant against many species of pest insect that infest food production facilities. Both its efficacy and method of application lead to very small amounts of the fumigant being used compared to other toxic substances used for the same purpose. Using HCN as a fumigant also has minimal environmental impact compared to similar structural fumigant molecules such as sulfuryl fluoride and methyl bromide


Occurrence

HCN is obtainable from
fruit In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the ...

fruit
s that have a pit, such as
cherries A cherry is the fruit In botany, a fruit is the seed-bearing structure in flowering plants (also known as angiosperms) formed from the ovary after flowering. Fruits are the means by which angiosperms disseminate seeds. Edible fru ...

cherries
,
apricot An apricot (, ) is a fruit In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The ...

apricot
s,
apple An apple is an edible fruit In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this fie ...

apple
s, and
bitter almond The almond (''Prunus dulcis'', syn. ''Prunus amygdalus'') is a species of tree native to Iran Iran ( fa, ایران ), also called Persia and officially the Islamic Republic of Iran ( fa, جمهوری اسلامی ایران ), is a ...
s, from which almond oil and flavoring are made. Many of these pits contain small amounts of
cyanohydrin A cyanohydrin or hydroxynitrile is a functional group found in organic compounds in which a cyano and a hydroxy group are attached to the same carbon atom. The general formula is R2C(OH)CN, where R is H, alkyl, or aryl. Cyanohydrins are industria ...

cyanohydrin
s such as
mandelonitrile In organic chemistry, mandelonitrile is the nitrile of mandelic acid, or the cyanohydrin derivative of benzaldehyde. Small amounts of mandelonitrile occur in the Drupe, pits of some fruits. Occurrence Mandelonitrile is the aglycone part of the c ...
and
amygdalin Amygdalin (from Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: ...

amygdalin
, which slowly release hydrogen cyanide. One hundred grams of crushed apple seeds can yield about 70 mg of HCN. So-called "bitter" roots of the
cassava ''Manihot esculenta'', commonly called cassava (), manioc, or yuca (among numerous regional names) is a woody shrub A shrub (often called a bush) is a small- to medium-sized perennial A perennial plant or simply perennial is a pla ...

cassava
plant may contain up to 1 gram of HCN per kilogram. Some
millipede Millipedes are a group of arthropods that are characterised by having two pairs of jointed arthropod leg, legs on most body segments; they are known scientifically as the class (biology), class Diplopoda, the name derived from this feature. Each ...

millipede
s, such as '' Harpaphe haydeniana'', '' Desmoxytes purpurosea'', and ''
Apheloria ''Apheloria'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology Biology is the natural science that studies life and living organisms, including their ...
'' release hydrogen cyanide as a defense mechanism, as do certain insects, such as burnet moths and the larvae of '' Paropsisterna eucalyptus''. Hydrogen cyanide is contained in the exhaust of vehicles, and in smoke from burning nitrogen-containing
plastic Plastics are a wide range of syntheticA synthetic is an artificial material produced by organic chemistry, organic chemical synthesis. Synthetic may also refer to: In the sense of both "combination" and "artificial" * Synthetic chemical or s ...

plastic
s.


HCN on Titan

HCN has been measured in Titan's atmosphere by four instruments on the Cassini space probe, one instrument on
Voyager Voyager may refer to: Computing and communications * LG Voyager The LG VX10000, also known as the Verizon Voyager or LG VX10K, is an Internet-enabled multimedia phone designed by LG Electronics and carried by Verizon Wireless, Telus, and Bel ...
, and one instrument on Earth. One of these measurements was ''in situ,'' where the Cassini spacecraft dipped between above Titan's surface to collect atmospheric gas for
mass spectrometry Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio The mass-to-charge ratio (''m''/''Q'') is a physical quantity A physical quantity is a physical property of a material or system that can be Quant ...
analysis. HCN initially forms in Titan's atmosphere through the reaction of photochemically produced methane and nitrogen radicals which proceed through the H2CN intermediate, e.g., (CH3 + N → H2CN + H → HCN + H2). Ultraviolet radiation breaks HCN up into CN + H; however, CN is efficiently recycled back into HCN via the reaction CN + CH4 → HCN + CH3.


HCN on the young Earth

It has been postulated that carbon from a cascade of asteroids (known as the
Late Heavy Bombardment The Late Heavy Bombardment (LHB), or lunar cataclysm, is a hypothesized event thought to have occurred approximately 4.1 to 3.8 billion year A year is the orbital period The orbital period is the time a given astronomical object takes ...
), resulting from interaction of Jupiter and Saturn, blasted the surface of young Earth and reacted with nitrogen in Earth's atmosphere to form HCN.


HCN in mammals

Some authors have shown that
neuron A neuron or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapse In the nervous system In biology Biology is the natural science that studies life and living ...

neuron
s can produce hydrogen cyanide upon activation of their
opioid Opioids are substances that act on opioid receptors to produce morphine-like effects. Medically they are primarily used for pain relief, including anesthesia. Other medical uses include suppression of diarrhea, replacement therapy for opioid use ...
receptors Receptor may refer to: *Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a ne ...

receptors
by endogenous or exogenous opioids. They have also shown that neuronal production of HCN activates
NMDA receptor The ''N''-methyl-D-aspartate receptor (also known as the NMDA receptor or NMDAR), is a glutamate receptor and ion channel found in Neuron, neurons. The NMDA receptor is one of three types of ionotropic glutamate receptors, the other two being A ...

NMDA receptor
s and plays a role in
signal transduction Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events, most commonly protein phosphorylation residue Protein phosphorylation is a reversible post-translational ...
between neuronal cells (
neurotransmission Neurotransmission (Latin: ''transmissio'' "passage, crossing" from ''transmittere'' "send, let through") is the process by which signaling molecules called neurotransmitter A neurotransmitter is a signaling molecule In biology, cell signal ...
). Moreover, increased endogenous neuronal HCN production under opioids was seemingly needed for adequate opioid
analgesia An analgesic or painkiller is any member of the group of drugs used to achieve analgesia, relief from pain Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain defines p ...
, as analgesic action of opioids was attenuated by HCN scavengers. They considered endogenous HCN to be a
neuromodulator Neuromodulation is the physiological Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology Biology is the natural science that studies life and living organisms, includi ...
. It has also been shown that, while stimulating muscarinic
cholinergic Cholinergic agents are compounds which mimic the action of acetylcholine Acetylcholine (ACh) is an that functions in the brain and body of many types of animals (including humans) as a —a chemical message released by nerve cells to sen ...
receptors in cultured
pheochromocytoma Pheochromocytoma (PHEO or PCC) is a rare tumor of the adrenal medulla composed of chromaffin cells, also known as pheochromocytes. When a tumor composed of the same cells as a pheochromocytoma develops outside the adrenal gland, it is referred t ...

pheochromocytoma
cells ''increases'' HCN production, in a living organism (''in vivo'') muscarinic cholinergic stimulation actually ''decreases'' HCN production.
Leukocyte White blood cells, also called leukocytes or leucocytes, are the of the that are involved in protecting the body against both and foreign invaders. All white blood cells are produced and derived from cells in the known as s. Leukocytes are ...
s generate HCN during
phagocytosis Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis Endocytosis is a cellular process i ...

phagocytosis
, and can kill
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
,
fungi A fungus (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full ...

fungi
, and other pathogens by generating several different toxic chemicals, one of which is hydrogen cyanide. The vasodilatation caused by
sodium nitroprusside Sodium nitroprusside (SNP), sold under the brand name Nitropress among others, is a medication used to lower blood pressure. This may be done if the hypertensive emergency, blood pressure is very high and resulting in symptoms, in certain types o ...
has been shown to be mediated not only by NO generation, but also by endogenous cyanide generation, which adds not only toxicity, but also some additional antihypertensive efficacy compared to
nitroglycerine Nitroglycerin (NG), also known as trinitroglycerin (TNG), nitro, glyceryl trinitrate (GTN), or 1,2,3-trinitroxypropane, is a dense, colorless, oily, explosive An explosive (or explosive material) is a reactive substance that contains a great ...
and other non-cyanogenic nitrates which do not cause blood cyanide levels to rise. HCN is a constituent of
tobacco smoke Tobacco smoke is a sooty Sooty is a British children's television Children's television series are television programs designed for children, normally scheduled for broadcast during the morning and afternoon when children are awake. They can ...
.


HCN and the origin of life

Hydrogen cyanide has been discussed as a precursor to amino acids and nucleic acids, and is proposed to have played a part in the
origin of life In evolutionary biology Evolutionary biology is the subfield of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molec ...
. Although the relationship of these chemical reactions to the origin of life theory remains speculative, studies in this area have led to discoveries of new pathways to organic compounds derived from the condensation of HCN (e.g.
Adenine Adenine (A, Ade) is a nucleobase 230px, Pyrimidine nucleobases are simple ring molecules. Nucleobases, also known as ''nitrogenous bases'' or often simply ''bases'', are nitrogen-containing biological compounds that form nucleosides Nucleos ...

Adenine
).


HCN in space

HCN has been detected in the
interstellar medium In astronomy Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of the stars) is a natural science that studies astronomical object, celestial objects and celestial event, phenomena. It uses math ...
and in the atmospheres of
carbon star A carbon star (C-type star) is typically an asymptotic giant branch star, a luminous red giant, whose Stellar atmosphere, atmosphere contains more carbon than oxygen. The two elements combine in the upper layers of the star, forming carbon monoxide, ...
s. Since then, extensive studies have probed formation and destruction pathways of HCN in various environments and examined its use as a tracer for a variety of astronomical species and processes. HCN can be from ground-based
telescope A telescope is an optical instrument An optical instrument (or "optic" for short) is a device that processes light waves (or photons), either to enhance an image for viewing or to analyze and determine their characteristic properties. Common ...

telescope
s through a number of
atmospheric An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or 'sphere') is a layer or a set of layers of gas Gas is one of the four fundamental states of matter In p ...

atmospheric
windows. The J=1→0, J=3→2, J= 4→3, and J=10→9 pure
rotational transitionA rotational transition is an abrupt change in angular momentum In physics, angular momentum (rarely, moment of momentum or rotational momentum) is the rotational equivalent of linear momentum. It is an important quantity in physics because it i ...
s have all been observed. HCN is formed in
interstellar Interstellar or Interstella may refer to: Space * Interstellar space ** Interstellar medium * Interstellar travel * Interstellar communication * Interstellar probe Art, entertainment, and media Films and soundtracks * ''Interstella 5555: The 5tor ...
clouds through one of two major pathways: via a neutral-neutral reaction (CH2 + N → HCN + H) and via dissociative recombination (HCNH+ + e → HCN + H). The dissociative recombination pathway is dominant by 30%; however, the HCNH+ must be in its linear form. Dissociative recombination with its structural isomer, H2NC+, exclusively produces
hydrogen isocyanide Hydrogen isocyanide is a chemical with the molecular formula HNC. It is a minor tautomer of hydrogen cyanide (HCN). Its importance in the field of astrochemistry is linked to its ubiquity in the interstellar medium. Nomenclature Both ''hydr ...
(HNC). HCN is destroyed in interstellar clouds through a number of mechanisms depending on the location in the cloud. In photon-dominated regions (PDRs), photodissociation dominates, producing (HCN + ν → CN + H). At further depths, photodissociation by cosmic rays dominate, producing CN (HCN + cr → CN + H). In the dark core, two competing mechanisms destroy it, forming HCN+ and HCNH+ (HCN + H+ → HCN+ + H; HCN + HCO+ → HCNH+ + CO). The reaction with HCO+ dominates by a factor of ~3.5. HCN has been used to analyze a variety of species and processes in the interstellar medium. It has been suggested as a tracer for dense molecular gas and as a tracer of stellar inflow in high-mass star-forming regions. Further, the HNC/HCN ratio has been shown to be an excellent method for distinguishing between PDRs and X-ray-dominated regions (XDRs). On 11 August 2014, astronomers released studies, using the Atacama Large Millimeter/Submillimeter Array (ALMA) for the first time, that detailed the distribution of HCN, HNC, H2CO, and
dust Dust is made of s of solid . On Earth, it generally consists of particles in the that come from various sources such as lifted by wind (an ), , and . Dust in homes is composed of about 20–50% dead . The rest, and in offices, and other ...
inside the comae of
comet A comet is an icy, small Solar System body A small Solar System body (SSSB) is an object in the Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astr ...

comet
s C/2012 F6 (Lemmon) and . In February 2016, it was announced that traces of hydrogen cyanide were found in the atmosphere of the hot
Super-Earth A super-Earth is an extrasolar planet with a mass higher than Earth's, but substantially below those of the Solar System's ice giants, Uranus and Neptune, which are 14.5 and 17 times Earth's, respectively. The term "super-Earth" refers only to th ...
55 Cancri e 55 Cancri e (abbreviated 55 Cnc e, formally named Janssen ) is an exoplanet in the orbit of its Sun-like host star 55 Cancri, 55 Cancri A. The mass of the exoplanet is about 8.63 Earth masses and its diameter is about twice that of the Earth, th ...

55 Cancri e
with NASA's
Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope A space telescope or space observatory is a telescope in outer space used to observe astronomical objects. Suggested by Lyman Spitzer in 1946, the first ...

Hubble Space Telescope
.


As a poison and chemical weapon

In
World War I World War I, often abbreviated as WWI or WW1, also known as the First World War or the Great War, was a global war A world war is "a war engaged in by all or most of the principal nations of the world". The term is usually reserved for ...

World War I
, hydrogen cyanide was used by the French from 1916 as a chemical weapon against the
Central Powers The Central Powers, also known as the Central Empires,german: Mittelmächte; hu, Központi hatalmak; tr, İttifak Devletleri / ; bg, Централни сили, translit=Tsentralni sili was one of the two main coalitions that fought World ...
, and by the United States and
Italy Italy ( it, Italia ), officially the Italian Republic ( it, Repubblica Italiana, links=no ), is a country consisting of a peninsula delimited by the Alps The Alps ; german: Alpen ; it, Alpi ; rm, Alps; sl, Alpe ) are the highest ...
in 1918. It was not found to be effective enough due to weather conditions. The gas is lighter than air and rapidly disperses up into the atmosphere. Rapid dilution made its use in the field impractical. In contrast, denser agents such as
phosgene Phosgene is the organic chemical compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, mo ...

phosgene
or
chlorine Chlorine is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemica ...

chlorine
tended to remain at ground level and sank into the
trenches A gas main being laid in a trench A trench is a type of excavation or depression in the ground that is generally deeper than it is wide (as opposed to a wider gully A gully is a landform A landform is a natural or artificial feature of the s ...

trenches
of the Western Front's battlefields. Compared to such agents hydrogen cyanide had to be present in higher concentrations in order to be fatal. A hydrogen cyanide concentration of 100–200 ppm in breathing air will kill a human within 10 to 60 minutes.Environmental and Health Effects
Cyanidecode.org. Retrieved on 2012-06-02.
A hydrogen cyanide concentration of 2000 ppm (about 2380 mg/m3) will kill a human in about one minute. The toxic effect is caused by the action of the cyanide ion, which halts
cellular respiration Cellular respiration is a set of metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities that have biological processes, such a ...

cellular respiration
. It acts as a non-competitive inhibitor for an enzyme in mitochondria called
cytochrome c oxidase The enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the ...
. As such, hydrogen cyanide is commonly listed among
chemical weapons A chemical weapon (CW) is a specialized munition that uses chemicals formulated to inflict death or harm on humans. According to the Organisation for the Prohibition of Chemical Weapons (OPCW), "the term chemical weapon may also be applied ...
as a
blood agent A blood agent is a toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is a ...
. The
Chemical Weapons Convention The Chemical Weapons Convention (CWC), officially the Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction, is an arms control Arms control is a term for international ...
lists it under Schedule 3 as a potential weapon which has large-scale industrial uses. Signatory countries must declare manufacturing plants that produce more than 30 metric tons per year, and allow inspection by the
Organisation for the Prohibition of Chemical Weapons The Organisation for the Prohibition of Chemical Weapons (OPCW) is an intergovernmental organisation An intergovernmental organization (IGO) is an organization composed primarily of sovereign states (referred to as ''member states''), or of ...
. Perhaps its most infamous use is (German: ''Cyclone B'', with the B standing for – prussic acid; also, to distinguish it from an earlier product later known as Zyklon A), it was used in
Nazi German Nazi Germany, (lit. "National Socialist State"), ' (lit. "Nazi State") for short; also ' (lit. "National Socialist Germany") officially known as the German Reich from 1933 until 1943, and the Greater German Reich from 1943 to 1945, was ...

Nazi German
extermination camps Nazi Germany Nazi Germany, (lit. "National Socialist State"), ' (lit. "Nazi State") for short; also ' (lit. "National Socialist Germany") officially known as the German Reich from 1933 until 1943, and the Greater German Reich fro ...
during
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a global war A world war is "a war War is an intense armed conflict between states State may refer to: Arts, entertainment, and media Literatur ...
to kill ''en masse'' as part of their
Final Solution The Final Solution (german: Endlösung, ) or the Final Solution to the Jewish Question (german: Endlösung der Judenfrage, ) was a Nazi Nazism ( ), officially National Socialism (german: Nationalsozialismus, ), is the ideology An i ...
genocide program. Hydrogen cyanide was also used in the camps for delousing clothing in attempts to eradicate diseases carried by lice and other parasites. One of the original Czech producers continued making Zyklon B under the trademark "Uragan D2" until recently. Hydrogen cyanide was also the agent employed in judicial
execution Capital punishment, also known as the death penalty, is the state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ' ...
in some
U.S. state In the United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state ...
s, where it was produced during the execution by the action of
sulfuric acid Sulfuric acid (American spelling Despite the various English dialects spoken from country to country and within different regions of the same country, there are only slight regional variations in English orthography English orthogra ...

sulfuric acid
on
sodium Sodium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical eleme ...

sodium
or
potassium cyanide Potassium cyanide is a compound with the formula In , a formula is a concise way of expressing information symbolically, as in a mathematical formula or a . The informal use of the term ''formula'' in science refers to the . The plural of ...
. Under the name ''prussic acid'', HCN has been used as a killing agent in
whaling Whaling is the process of hunting of whales for their usable products such as Whale meat, meat and blubber, which can be turned into Whale oil, a type of oil that became increasingly important in the Industrial Revolution. It was practiced as ...

whaling
harpoons, although it proved quite dangerous to the crew deploying it, and was quickly abandoned. From the middle of the 18th century it was used in a number of poisoning murders and suicides. Hydrogen cyanide gas in air is explosive at concentrations above 5.6%. This concentration is far above a toxic level.


References


External links

*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'')

( CICAD 61)
National Pollutant Inventory: Cyanide compounds fact sheetDepartment of health reviewDensity of Hydrogen Cyanide gas
{{DEFAULTSORT:Hydrogen Cyanide Blood agents Cyanides Fumigants Hydrogen compounds Inorganic compounds Gaseous signaling molecules Soviet chemical weapons program