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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 chemical bonds. A homonuclear molecule, m ...
that contains the group C≡N. This group, known as the cyano group, consists of a
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
atom
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 ...
ed to a
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
atom. In
inorganic 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, behavior and the changes they under ...
cyanides, the cyanide group is present as the anion CN. Soluble
salts 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 undergo during ...
such as
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 ...
are highly toxic.
Hydrocyanic acid Hydrogen cyanide, sometimes called prussic acid, is a chemical compound with the chemical formula HCN. It is a colorless, extremely poisonous, and flammable liquid that boiling, boils slightly above room temperature, at . HCN is produced on an in ...
, also known as hydrogen cyanide, or HCN, is a highly volatile liquid that is produced on a large scale industrially. It is obtained by acidification of cyanide salts.
Organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organic matter, matter that has come from a once-living organism, is capable of decay or ...
cyanides are usually called
nitrile A nitrile is any 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, cat ...
s. In nitriles, the CN group is linked by a
covalent bond A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs, and the stable balance of attractive and repulsive forces between atoms, when they s ...
to carbon. For example, in
acetonitrile Acetonitrile, often abbreviated MeCN (methyl cyanide), is the 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 chem ...

acetonitrile
, the cyanide group is bonded to
methyl A methyl group is an alkyl In organic chemistry, an alkyl substituent is an alkane missing one hydrogen. The term alkyl is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of C''n''H2' ...

methyl
(CH3). Alhough nitriles generally do not release cyanide ions, the
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 indust ...

cyanohydrin
s do and are thus rather toxic. The word is derived from the Greek ''kyanos'', meaning dark blue, as a result of its being first obtained by the heating of the pigment known as
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
.


Bonding

The cyanide ion is
isoelectronic Isoelectronicity is an effect observed when two or more molecules have the same Chemical structure, structure (positions and connectivities among atoms) and the same electron configurations, but differ by what specific elements are at certain loc ...
with
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 with molecular
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
. A triple bond exists between N and C. The negative charge is concentrated on carbon.


Occurrence


In nature

Cyanides are produced by certain
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 ...
,
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
algae Algae (; singular alga ) is an informal term for a large and diverse group of s. It is a grouping that includes species from multiple distinct s. Included organisms range from , such as '','' and the s, to forms, such as the , a large whi ...

algae
. It is an
antifeedant Antifeedants are s produced by plants to inhibit attack by insects and grazing animals. These chemical compounds are typically classified as s in that they are not essential for the metabolism of the plant, but instead confer longevity. Antifeedant ...
in a number of plants. Cyanides are found in substantial amounts in certain seeds and fruit stones, e.g., those of
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,
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 produced by an apple tree (''Malus domestica''). Apple fruit tree, trees are agriculture, cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, wher ...

apple
s, and
peach The peach (''Prunus persica'') is a deciduous In the fields of horticulture Horticulture is the art of cultivating plants in gardens to produce food and medicinal ingredients, or for comfort and ornamental purposes. Horticulturists grow ...

peach
es. Chemical compounds that can release cyanide are known as cyanogenic compounds. In plants, cyanides are usually bound to
sugar Sugar is the generic name for sweet-tasting, soluble carbohydrate is a disaccharide A disaccharide (also called a double sugar or ''biose'') is the sugar formed when two monosaccharides are joined by glycosidic linkage. Like monosacc ...

sugar
molecules in the form of cyanogenic
glycoside In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of atoms ...

glycoside
s and defend the plant against
herbivore A herbivore is an animal Animals (also called Metazoa) are organisms that form the Animalia. With few exceptions, animals , , are , can , and grow from a hollow sphere of , the , during . Over 1.5 million animal have been —of ...
s.
Cassava ''Manihot esculenta'', commonly called cassava (), manioc, or yuca (among numerous regional names) is a woody shrub A shrub (or bush, but this is more of a gardening term) is a small- to medium-sized perennial woody plant. Unlike herb ...

Cassava
roots (also called manioc), an important
potato The potato is a starch#Food, starchy tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial plant, perennial in the nightshade family Solanaceae. Wild potato species can be found thro ...

potato
-like food grown in tropical countries (and the base from which
tapioca Tapioca (; ) is a starch Starch or amylum is a consisting of numerous units joined by s. This is produced by most green s for energy storage. Worldwide, it is the most common carbohydrate in human diets, and is contained in large amounts ...

tapioca
is made), also contain cyanogenic glycosides. The
Madagascar Madagascar (; mg, Madagasikara), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), and previously known as the Malagasy Republic The Malagasy Republic ( mg, Repoblika Mala ...

Madagascar
bamboo ''
Cathariostachys madagascariensis ''Cathariostachys madagascariensis'', the Madagascar giant bamboo or volohosy in Malagasy Malagasy may refer to: *Someone or something from Madagascar *Malagasy people *Malagasy language *Malagasy Republic *Related to the culture of Madagascar ...
'' produces cyanide as a deterrent to grazing. In response, the golden bamboo lemur, which eats the bamboo, has developed a high tolerance to cyanide.


Interstellar medium

The cyanide radical ·CN has been identified in
interstellar space Outer space, commonly shortened to space, is the expanse that exists beyond Earth and Earth atmosphere, its atmosphere and between astronomical object, celestial bodies. Outer space is not completely empty—it is a hard vacuum containing a ...
.
Cyanogen Cyanogen is the 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 chemica ...

Cyanogen
, (CN)2, is used to measure the temperature of interstellar gas clouds.


Pyrolysis and combustion product

Hydrogen cyanide is produced by the combustion or
pyrolysis The pyrolysis (or devolatilization) process is the of materials at elevated temperatures in an inert atmosphere. It involves a change of . The word is coined from the -derived s ''pyro'' "fire" and ' "separating". Pyrolysis is most commonly us ...

pyrolysis
of certain materials under oxygen-deficient conditions. For example, it can be detected in the exhaust of
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and ...

internal combustion engine
s and
tobacco Tobacco is the common name of several plants in the ' of the , and the general term for any product prepared from the of these plants. of tobacco are known, but the chief commercial crop is . The more potent variant is also used in som ...

tobacco
smoke. Certain
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, especially those derived from
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 ...
, release hydrogen cyanide when heated or burnt.


Cofactor

The
hydrogenaseA hydrogenase is an 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 c ...
enzymes contain cyanide
ligand In coordination chemistry A coordination complex consists of a central 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 havi ...
s attached to iron in their active sites. The biosynthesis of cyanide in the iFehydrogenases proceeds from
carbamoyl phosphate Carbamoyl phosphate is an anion An ion () is a particle, atom or molecule with a net electric charge, electrical charge. The charge of the electron is considered negative by convention. The negative charge of an ion is equal and opposite to ...
, which converts to cysteinyl
thiocyanate Thiocyanate (also known as rhodanide) is 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 ...
, the CN donor.


Organic derivatives

In
IUPAC nomenclature The International Union of Pure and Applied Chemistry The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a m ...
,
organic compound 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 undergo during ...
s that have a –C≡N
functional group In organic chemistry, a functional group is a substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions re ...
are called
nitrile A nitrile is any 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, cat ...
s. An example of a nitrile is CH3CN,
acetonitrile Acetonitrile, often abbreviated MeCN (methyl cyanide), is the 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 chem ...

acetonitrile
. Nitriles usually do not release cyanide ions. A functional group with a hydroxyl and cyanide bonded to the same carbon is called
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 indust ...

cyanohydrin
. Unlike nitriles, cyanohydridins do release
hydrogen cyanide 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 ...

hydrogen cyanide
. In inorganic chemistry, salts containing the C≡N ion are referred to as cyanides. Although the cyanide ion contains a carbon atom, it is not usually considered organic.


Reactions


Protonation

Cyanide is basic. The pKa of hydrogen cyanide is 9.21. Thus, addition of acid to solutions of cyanide salts releases
hydrogen cyanide 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 ...

hydrogen cyanide
.


Hydrolysis

Cyanide is unstable in water, but the reaction is slow until about 170 °C. It undergoes
hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution Substitution may refer to: Arts and media *Chord substitution, in music, swapping one chord fo ...

hydrolysis
to give
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
and
formate Formate (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Science Coun ...

formate
, which are far less toxic than cyanide: :CN + 2H2O → HCO2 + NH3 cyanide hydrolase is an enzyme that catalyze this reaction.


Alkylation

Because of the cyanide anion's high
nucleophilicity 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, behavior and the changes they underg ...

nucleophilicity
, cyano groups are readily introduced into organic molecules by displacement of a
halide A halide is a binary phase, of which one part is a halogen atom and the other part is an chemical element, element or radical (chemistry), radical that is less electronegative (or more electropositive) than the halogen, to make a, e.g., fluoride, ...
group (e.g., the
chloride The chloride ion 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 everyday objects th ...

chloride
on
methyl chloride Chloromethane, also called methyl chloride, Refrigerant-40, R-40 or HCC 40, is an organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements a ...
). In general, organic cyanides are called nitriles. In organic synthesis, cyanide is a C-1
synthon In retrosynthetic analysis Retrosynthetic analysis is a technique for solving problems in the planning of organic syntheses ''Organic Syntheses'' is a peer-reviewed scientific journal that was established in 1921. It publishes detailed and chec ...

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


Redox

The cyanide ion is a
reductant A reducing agent (also called a reductant or reducer) is an element or compound that loses (or "donates") an electron to an electron recipient (oxidizing agent) in a redox chemical reaction. A reducing agent is thus oxidized when it loses electrons ...
and is
oxidized (mild reducing agent) are added to powdered potassium permanganate (strong oxidizing agent), a violent redox reaction accompanied by self-ignition starts. Redox (reduction–oxidation, pronunciation: or ) is a type of chemical reaction A ...

oxidized
by strong
oxidizing agent An oxidizing agent, also known as an oxidant or oxidizer, is a substance that has the ability to oxidize other substances — in other words to electron acceptor, accept their electrons. Common oxidizing agents are oxygen, hydrogen peroxi ...

oxidizing agent
s such as molecular
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
(Cl2),
hypochlorite In chemistry, hypochlorite is an anion with the chemical formula ClO−. It combines with a number of cations to form hypochlorite salts. Common examples include sodium hypochlorite (household bleach) and calcium hypochlorite (a component of ble ...
(ClO), and
hydrogen peroxide Hydrogen peroxide is a chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by hav ...

hydrogen peroxide
(H2O2). These oxidizers are used to destroy cyanides in
effluent Effluent is an outflowing of water or gas to a natural body of water, from a structure such as a wastewater treatment plant, sewer pipe, or industrial outfall. Effluent, in engineering, is the stream exiting a chemical reactor A chemical reactor ...
s from
gold mining Gold mining is the extraction of gold Gold is a 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 consisti ...
.Young, C. A., & Jordan, T. S. (1995, May). Cyanide remediation: current and past technologies. In: Proceedings of the 10th Annual Conference on Hazardous Waste Research (pp. 104-129). Kansas State University: Manhattan, KS. https://engg.ksu.edu/HSRC/95Proceed/young.pdfBotz Michael M. Overview of cyanide treatment methods. Elbow Creek Engineering, Inc. http://www.botz.com/MEMCyanideTreatment.pdf


Metal complexation

The cyanide anion reacts with
transition metals In chemistry, the term transition metal (or transition element) has three possible definitions: * The IUPAC definition defines a transition metal as "an chemical element, element whose atom has a partially filled Electron shell, ''d'' sub-shel ...
to form M-CN bondss. This reaction is the basis of cyanide's toxicity. The high affinities of metals for this
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 everyday objects that can be touched are ...
can be attributed to its negative charge, compactness, and ability to engage in π-bonding. Among the most important cyanide coordination compounds are the
potassium ferrocyanide Potassium ferrocyanide is the inorganic compound with formula K4 e(CN)63H2O. It is the potassium salt of the complex (chemistry), coordination complex e(CN)6−. This salt forms lemon-yellow monoclinic crystals. Synthesis In 1752, the F ...

potassium ferrocyanide
and the 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 are both essentially nontoxic due to the tight binding of the cyanides to a central iron atom. Prussian blue was first accidentally made around 1706, by heating substances containing iron and carbon and nitrogen, and other cyanides made subsequently (and named after it). Among its many uses, Prussian blue gives the blue color to
blueprints A blueprint is a reproduction of a technical drawing Technical drawing, drafting or drawing, is the act and discipline Discipline is action ACTION is a bus operator in Canberra Canberra ( ) is the capital city of Australi ...

blueprints
, bluing, and
cyanotype Image:Joy_Oil_gas_station_blueprints.jpg, Architectural drawing blueprint, Canada, 1936 Cyanotype is a photographic process, photographic printing process that produces a cyan, cyan-blue print. Engineers used the process well into the 20th centu ...

cyanotype
s.


Manufacture

The principal process used to manufacture cyanides is the
Andrussow process File:1931.01.31 23 Andrussow Pilot Plant diagramm Herne Germany.jpg, Diagram from 1931 showing the Andrussow process The Andrussow process is an industrial process for the production of hydrogen cyanide from methane and ammonia in the presence of ox ...
in which gaseous
hydrogen cyanide 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 ...

hydrogen cyanide
is produced from
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
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
and 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 Catalysis () is the process of increasing the rate of a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter In cla ...

catalyst
. :2 CH4 + 2 NH3 + 3 O2 → 2 HCN + 6 H2O Sodium cyanide, the precursor to most cyanides, is produced by treating
hydrogen cyanide 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 ...

hydrogen cyanide
with
sodium hydroxide Sodium hydroxide, also known as lye A lye is a metal hydroxide traditionally obtained by leaching wood ashes, or a strong alkali In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chem ...

sodium hydroxide
: :HCN + NaOH → NaCN + H2O


Toxicity

Many cyanides are highly toxic. The cyanide anion is an inhibitor of 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 substrates in ...

enzyme
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 su ...
(also known as aa3), the fourth complex of the
electron transport chain An electron transport chain (ETC) is a series of protein complex A protein complex or multiprotein complex is a group of two or more associated polypeptide chain Peptides (from Greek language Greek (modern , romanized: ''Elliniká'', Anc ...

electron transport chain
found in the inner membrane of the
mitochondria A mitochondrion (; ) is a double-membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Biological membranes include cell membranes ...

mitochondria
of
eukaryotic Eukaryotes () are organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interact ...

eukaryotic
cells. It attaches to the iron within this protein. The binding of cyanide to this enzyme prevents transport of electrons from
cytochrome c The cytochrome complex, or cyt ''c'', is a small hemeprotein found loosely associated with the inner membrane of the mitochondrion A mitochondrion (, plural mitochondria) is a double membrane-bound organelle In cell biology, an organelle i ...

cytochrome c
to oxygen. As a result, the electron transport chain is disrupted, meaning that the cell can no longer aerobically produce
ATP ATP may refer to: Companies and organizations * Association of Tennis Professionals * American Technical Publishers * ', a Danish pension * Armenia Tree Project * Association for Transpersonal Psychology * ATP architects engineers office * ATP ...

ATP
for energy. Tissues that depend highly on
aerobic respiration Aerobic means "requiring air File:Atmosphere gas proportions.svg, Composition of Earth's atmosphere by volume, excluding water vapor. Lower pie represents trace gases that together compose about 0.043391% of the atmosphere (0.04402961% at Apr ...
, such as the
central nervous system The central nervous system (CNS) is the part of the nervous system In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecu ...

central nervous system
and the
heart The heart is a muscular MUSCULAR (DS-200B), located in the United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' use ...

heart
, are particularly affected. This is an example of histotoxic hypoxia. The most hazardous compound is
hydrogen cyanide 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 ...

hydrogen cyanide
, which is a gas and kills by inhalation. For this reason, an air respirator supplied by an external oxygen source must be worn when working with hydrogen cyanide. Hydrogen cyanide is produced by adding acid to a solution containing a cyanide salt. Alkaline solutions of cyanide are safer to use because they do not evolve hydrogen cyanide gas. Hydrogen cyanide may be produced in the combustion of
polyurethane Polyurethane (often abbreviated PUR and PU) referes to a class of polymers composed of organic chemistry, organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane ...

polyurethane
s; for this reason, polyurethanes are not recommended for use in domestic and aircraft furniture. Oral ingestion of a small quantity of solid cyanide or a cyanide solution of as little as 200 mg, or exposure to airborne cyanide of 270 ppm, is sufficient to cause death within minutes. Organic
nitrile A nitrile is any 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, cat ...
s do not readily release cyanide ions, and so have low toxicities. By contrast, compounds such as
trimethylsilyl cyanide Trimethylsilyl cyanide is the 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 toget ...
(CH3)3SiCN readily release HCN or the cyanide ion upon contact with water.


Antidote

Hydroxocobalamin reacts with cyanide to form cyanocobalamin, which can be safely eliminated by the kidneys. This method has the advantage of avoiding the formation of methemoglobin (see below). This antidote kit is sold under the brand name Cyanokit and was approved by the U.S. FDA in 2006. An older cyanide antidote kit included administration of three substances: amyl nitrite pearls (administered by inhalation), sodium nitrite, and sodium thiosulfate. The goal of the antidote was to generate a large pool of ferric iron (Fe3+) to compete for cyanide with cytochrome a3 (so that cyanide will bind to the antidote rather than the enzyme). The nitrites oxidize hemoglobin to methemoglobin, which competes with cytochrome oxidase for the cyanide ion. Cyanmethemoglobin is formed and the cytochrome oxidase enzyme is restored. The major mechanism to remove the cyanide from the body is by enzymatic conversion to
thiocyanate Thiocyanate (also known as rhodanide) is 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 ...
by the mitochondrial enzyme rhodanese. Thiocyanate is a relatively non-toxic molecule and is excreted by the kidneys. To accelerate this detoxification, sodium thiosulfate is administered to provide a sulfur donor for rhodanese, needed in order to produce thiocyanate.


Sensitivity

Minimum risk levels (MRLs) may not protect for delayed health effects or health effects acquired following repeated sublethal exposure, such as hypersensitivity, asthma, or bronchitis. MRLs may be revised after sufficient data accumulates.


Applications


Mining

Cyanide is mainly produced for the mining of gold and silver: It helps dissolve these metals allowing separation from the other solids. In the ''cyanide process'', finely ground high-grade ore is mixed with the cyanide (at a ratio of about 1:500 parts NaCN to ore); low-grade ores are stacked into heaps and sprayed with a cyanide solution (at a ratio of about 1:1000 parts NaCN to ore). The precious metals are complexed by the cyanide
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 everyday objects that can be touched are ...
s to form soluble derivatives, e.g., [Au(CN)2] and [Ag(CN)2]. Silver is less Noble metal, "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: 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. A number of List of gold mining disasters, environmental disasters have followed the overflow of tailing ponds at gold mines. Cyanide contamination of waterways has resulting in numerous cases of human and aquatic species mortality. 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. Gold-containing arsenopyrite ores are similarly reactive toward inorganic cyanide.


Industrial organic chemistry

The second major application of alkali metal cyanides (after mining) is in the production of CN-containing compounds, usually nitriles. Acyl cyanides are produced from acyl chlorides and cyanide.
Cyanogen Cyanogen is the 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 chemica ...

Cyanogen
, cyanogen chloride, and the trimer cyanuric chloride are derived from alkali metal cyanides.


Medical uses

The cyanide compound sodium nitroprusside is used mainly in clinical chemistry to measure urine ketone bodies mainly as a follow-up to diabetic patients. On occasion, it is 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. The cobalt in artificial Vitamin B12, vitamin B12 contains a cyanide ligand as an artifact of the purification process; this must be removed by the body before the vitamin molecule can be activated for biochemical use. During World War I, a copper cyanide compound was briefly used by Japanese physicians for the treatment of tuberculosis and leprosy.


Illegal fishing and poaching

Cyanides are illegally used to capture live fish near coral reefs for the aquarium and seafood markets. The practice is controversial, dangerous, and damaging but is driven by the lucrative exotic fish market.Dzombak, David A; Ghosh, Rajat S; Wong-Chong, George M. ''Cyanide in Water and Soil''. CRC Press, 2006, Chapter 11.2: "Use of Cyanide for Capturing Live Reef Fish". Poachers in Africa have been known to use cyanide to poison waterholes, to kill elephants for their ivory.


Pest control

M44 (cyanide device), M44 cyanide devices are used in the United States to kill coyotes and other canids. Cyanide is also used for pest control in New Zealand, particularly for Common Brushtail Possum in New Zealand, possums, an introduced marsupial that threatens the conservation of native species and spreads tuberculosis amongst cattle. Possums can become bait shy but the use of pellets containing the cyanide reduces bait shyness. Cyanide has been known to kill native birds, including the endangered Kiwi (bird), kiwi. Cyanide is also effective for controlling the dama wallaby, another introduced marsupial pest in New Zealand. A licence is required to store, handle and use cyanide in New Zealand. Cyanides are used as insecticides for fumigating ships. Cyanide salts are used for killing ants, and have in some places been used as rat poison (the less toxic poison arsenic is more common).


Niche uses

Potassium ferrocyanide is used to achieve a blue color 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. Cyanide is also used in jewelry-making and certain kinds of photography such as sepia toning. Although usually thought to be toxic, cyanide and cyanohydrins increase germination in various plant species.


Human poisoning

Deliberate cyanide poisoning of humans has occurred many times throughout history. Common salts such as
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
are involatile but water soluble, so are poisonous by ingestion. Hydrogen cyanide is a gas, making it more indiscriminately dangerous, however it is lighter than air and rapidly disperses up into the atmosphere, which makes it ineffective as a chemical weapon. Poisoning by hydrogen cyanide is more effective in an enclosed space, such as a gas chamber. Most significantly, hydrogen cyanide released from pellets of Zyklon-B was used extensively in the extermination camps of the Holocaust.


Food additive

Due to the high stability of their complexation with iron, ferrocyanides (Sodium ferrocyanide E535, Potassium ferrocyanide E536, and Calcium ferrocyanide E538) do not decompose to lethal levels in the human body and are used in the food industry as, e.g., an anticaking agent in table salt.


Chemical tests for cyanide

Cyanide is quantified by potentiometric titration, a method widely used in gold mining. It can also be determined by titration with silver ion. Some analyses begin with an air-purge of an acidified boiling solution, sweeping the vapors into a basic absorber solution. The cyanide salt absorbed in the basic solution is then analyzed.


Qualitative tests

Because of the notorious toxicity of cyanide, many methods have been investigated. Benzidine gives a blue coloration in the presence of ferricyanide. Iron(II) sulfate added to a solution of cyanide, such as the filtrate from the sodium fusion test, gives prussian blue. A solution of 1,4-Benzoquinone, ''para''-benzoquinone in dimethyl sulfoxide, DMSO reacts with inorganic cyanide to form a cyanophenol, which is fluorescent. Illumination with a UV light gives a green/blue glow if the test is positive.


References


External links


ATSDR medical management guidelines for cyanide poisoning (US)
*[http://www.inchem.org/documents/cicads/cicads/cicad61.htm Hydrogen cyanide and cyanides] (CICAD 61)
IPCS/CEC Evaluation of antidotes for poisoning by cyanidesEating apple seeds is safe despite the small amount of cyanideToxicological Profile for Cyanide, U.S. Department of Health and Human Services, July 2006
Safety data (French): * Institut national de recherche et de sécurité (1997).
Cyanure d'hydrogène et solutions aqueuses
. ''Fiche toxicologique n° 4'', Paris: INRS, 5 pp. (PDF file, ) * Institut national de recherche et de sécurité (1997).
Cyanure de sodium. Cyanure de potassium
. ''Fiche toxicologique n° 111'', Paris: INRS, 6 pp. (PDF file, ) {{Authority control Cyanides, Anions Blood agents Nitrogen(−III) compounds Toxicology