Hydrogen cyanide
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{{Chembox new
| Name = Hydrogen cyanide
| ImageFileL1 = Hydrogen-cyanide-2D.png
| ImageSizeL1 = 100px
| ImageNameL1 = Chemical structure of hydrogen cyanide manny
| ImageFileR1 = Hydrogen-cyanide-3D-vdW.png
| ImageSizeR1 = 120px
| ImageNameR1 = Hydrogen cyanide
| IUPACName = hydrogen cyanide<br />methanenitrile<br />hydridonitridocarbon
| OtherNames = Hydrocyanic acid<br />prussic acid<br/>formonitrile<br />formic anammonide<br/>carbon hydride nitride<br />cyanane<br />cyclon
| Section1 = {{Chembox Identifiers
| CASNo = 74-90-8
| RTECS = MW6825000
| SMILES = C#N
}}
| Section2 = {{Chembox Properties
| Formula = HCN
| MolarMass = 27.03 g/mol
| Appearance = Colorless gas or pale blue<br/>highly volatile liquid
| Density = 0.687 g/cm³, liquid.
| Solubility = Completely miscible.
| MeltingPt = -13.4°C (259.75 K, 7.88°F)
| BoilingPt = 26°C (299.15 K, 78.8°F)
| pKa = 9.2 - 9.3
}}| Section7 = {{Chembox Hazards
| MainHazards = Highly toxic, highly flammable.
| Section3 = {{Chembox Structure
| MolShape = Linear
| Dipole = 2.98 [[Debye|D]]
}}
| NFPA-H = 4
| NFPA-F = 4
| NFPA-R = 2
| FlashPt = −17.78 °C
| RPhrases = {{R12}}, {{R26}}, {{R27}}, {{R28}}, {{R32}}.
| SPhrases = {{S1}}, {{S2}}, {{S7}}, {{S9}}, {{S13}}, {{S16}},<br />{{S28}}, {{S29}}, {{S45}}.
}}
| Section8 = {{Chembox Related
| OtherCpds = [[Cyanogen]]<br />[[Cyanogen chloride]]<br/>[[trimethylsilyl cyanide]]
}}
}}
'''Hydrogen cyanide''' is a [[chemical compound]] with [[chemical formula]] HCN. A [[solution]] of hydrogen cyanide in [[water (molecule)|water]] is called hydrocyanic acid. Hydrogen cyanide is a [[color]]less, very [[poison]]ous, and highly [[volatility (chemistry)|volatile]] liquid that [[boiling|boils]] slightly above [[room temperature]] at 26 [[Celsius|°C]] (78.8 [[Fahrenheit|°F]]). HCN has a faint, bitter, [[almond]]-like [[odor]] that some people are unable to [[olfactory system|detect]] due to a [[gene]]tic [[Trait (biological)|trait]].<ref>[[Online Mendelian Inheritance in Man]], [http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=304300 Cyanide, inability to smell]</ref> Hydrogen cyanide is weakly [[acid]]ic and partly [[ionization|ionizes]] in solution to give the [[cyanide|cyanide anion]], CN<sup>–</sup>. The [[salt]]s of hydrogen cyanide are known as [[cyanide]]s. HCN is a highly valuable precursor to many chemical compounds ranging from polymers to pharmaceuticals.
==Production and synthesis==
Hydrogen cyanide is currently produced in large quantities by three processes. In the year 2000, 1.615 billion pounds (732,552 tons) were produced in the US.[http://www.the-innovation-group.com/ChemProfiles/Hydrogen%20Cyanide.htm] The most important process for the production of hydrogen cyanide is the [[Andrussov oxidation]] invented by [[Leonid Andrussow]] in which [[methane]] and [[ammonia]] react in the presence of [[oxygen]] at about 1200 °C over a [[platinum]] catalyst:<ref>{{cite journal
| title = The catalytic oxydation of ammonia-methane-mixtures to hydrogen cyanide.
| author = L. Andrussow
| journal = Angewandte Chemie
| year = 1935
| volume = 48
| issue =
| pages = 593–595
| doi =
}}</ref>
::2CH<sub>4</sub> + 2NH<sub>3</sub> + 3O<sub>2</sub> → 2HCN + 6H<sub>2</sub>O
The energy needed for the reaction is provided by the part oxidation of methane and ammonia.
Of lesser importance is the [[Degussa]] process (BMA process) in which no oxygen is added and the energy must be transferred indirectly through the reactor wall:<ref>{{cite journal
| title = Die technische Synthese von Cyanwasserstoff aus Methan und Ammoniak ohne Zusatz von Sauerstoff
| author = F. Endter
| journal = Chemie Ingenieur Technik
| year = 1958
| volume = 30
| issue = 5
| pages = 281–376
| doi = 10.1002/cite.330300506
}}</ref>
::CH<sub>4</sub> + NH<sub>3</sub> → HCN + 3H<sub>2</sub>
This reaction is akin to [[steam reforming]], the reaction of [[methane]] and water.
In another process, practiced at [[BASF]], [[formamide]] is heated and split into hydrogen cyanide and water:
::CH(O)NH<sub>2</sub> → HCN + H<sub>2</sub>O
In the laboratory, small amounts of HCN are produced by the addition of acids to cyanide salts of alkali metals:
::H<sup>+</sup> + NaCN → HCN + Na<sup>+</sup>
This reaction is sometimes the basis of accidental poisonings because the acid converts a nonvolatile cyanide salt into the gaseous HCN.
===History===
The first source for hydrogen cyanide was the reaction of acid on [[ferrocyanide]]s. The rising demand due to the use of cyanides for mining operations in the 1890s was met by the '''[[Bleiby process]]'''. [[George Thomas Beilby]] patented a method to produce hydrogen cyanide by passing [[ammonia]] over glowing [[coal]] in 1892. This method was used until [[Hamilton Castner]] in 1894 developed a synthesis starting from coal, ammonia and [[sodium]] yielding sodium cyanide, which reacts with acid to form gaseous HCN.
==Reactions==
HCN adds to [[ketone]]s and [[aldehyde]]s to give [[cyanohydrin]]s. Amino acids are prepared by this reaction; the essential [[amino acid]] [[methionine]] is manufactured by this route.The cyanohydrin of [[acetone]] is a precursor to [[methyl methacrylate]].{{Fact|date=February 2007}}
In [[hydrocyanation]], HCN adds to [[alkene]]s to give nitriles. This reaction is employed to manufacture [[adiponitrile]], the precursor to [[Nylon|Nylon 66]].
==Occurrence and applications==
Cyanide is used in [[tempering]] [[steel]], [[dye]]ing, [[explosive]]s, [[engraving]], the production of [[Polymethyl methacrylate|acrylic resin plastic]], and other organic chemical products (eg: historically: [[formic acid]]). The less toxic [[ethyl acetate]] (C<sub>4</sub>H<sub>8</sub>O<sub>2</sub>) has now largely replaced the use of cyanide in [[insect]] [[killing jar]]s. Cyanide is also being used for [[capital punishment]]{{Fact|date=February 2008}}.
[[Fruit]]s that have a pit, such as [[cherry|cherries]] and [[apricot]]s, [[Almond#Sweet and bitter almonds|bitter almond]]s and [[apples]], from which almond oil and flavoring are made, contain small amounts of [[cyanohydrin]]s such as [[mandelonitrile]] (CAS#532-28-5). Such molecules slowly release hydrogen cyanide.<ref>{{cite journal | author= J. Vetter| title= Plant cyanogenic glycosides | journal=Toxicon. | year= 2000 | volume=38 | pages=11–36|doi=10.1016/S0041-0101(99)00128-2 }}</ref><ref>{{cite journal | author= D. A. Jones | title= Why are so many food plants cyanogenic? | journal=Phytochemistry | year= 1998 | volume=47 | pages=155–162 |doi=10.1016/S0031-9422(97)00425-1 }}</ref> Some [[millipede]]s release hydrogen cyanide as a defense mechanism,<ref> {{cite journal | author= M. S. Blum, J. P. Woodring| title= Secretion of Benzaldehyde and Hydrogen Cyanide by the Millipede ''[[Pachydesmus crassicutis]]'' (Wood) | journal=[[Science]] | year= 1962 | volume=138 | pages=512–513|doi=10.1126/science.138.3539.512| pmid= 17753947 }}</ref> as do certain insects such as some [[Zygaenidae|burnet moth]]s. Hydrogen cyanide is contained in the exhaust of vehicles, in [[tobacco]] and wood smoke, and in smoke from burning nitrogen-containing [[plastics]].
100 g of crushed apple seeds can yield 219 mg of [[Amygdalin]] which can generate ~10 mg of HCN.{{Fact|date=February 2007}}
==HCN and the origin of life==
Hydrogen cyanide has been discussed as a precursor to amino acids and nucleic acids. It is possible, for example, that HCN played a part in the [[origin of life]]. [[Leslie Orgel]], among many researchers, has written extensively on the condensation of HCN.<ref>Matthews, C. N. "The HCN World: Establishing Protein-Nucleic Augucid Life via Hydrogen Cyanide Polymers" Cellular Origin and Life in Extreme Habitats and Astrobiology (2004), 6 (Origins : Genesis, Evoluation and Diversity of Life), 121-135.</ref> Although the relationship of these chemical reactions to the origin of life remains speculative, studies in this area have led to discoveries of new pathways to organic compounds derived from condensation of HCN.<ref>Al-Azmi, A.; Elassar, A.-Z. A.; Booth, B. L. "The Chemistry of Diaminomaleonitrile and its Utility in Heterocyclic Synthesis" Tetrahedron (2003), 59, 2749-2763. CODEN: TETRAB ISSN:0040-4020</ref>
==Hydrogen cyanide as a poison and chemical weapon==
:''See also: [[cyanide poisoning]]''
An HCN concentration of 300 mg/m<sup>3</sup> in air will kill a [[homo sapiens|human]] within a few minutes.<ref>[http://www.osha.gov/SLTC/healthguidelines/hydrogencyanide/recognition.html Hydrogen Cyanide<!-- Bot generated title -->]</ref> The toxicity is caused by the [[cyanide]] ion, which prevents [[cellular respiration]]. Hydrogen cyanide (under the brand name [[Zyklon B]]) was perhaps most infamously employed by the [[Nazi Germany|Nazi]] regime in mid-20th century.
Hydrogen cyanide is commonly listed amongst [[chemical warfare agent]]s that cause general poisoning.<ref>{{cite web | url = http://www.opcw.org/resp/html/hcn.html | title = Hydrogen Cyanide | work = Organisation for the Prohibition of Chemical Weapons | accessdate = 2006-10-07}}</ref> As a substance listed under [[List of Schedule 3 substances (CWC)|Schedule 3]] of the [[Chemical Weapons Convention]] as a potential weapon which has large-scale industrial uses, manufacturing plants in signatory countries which produce more than 30 tonnes per year must be declared to, and can be inspected by, the [[Organisation for the Prohibition of Chemical Weapons|OPCW]].
Hydrogen cyanide gas in air is explosive at concentrations over 5.6%, equivalent to 56,000 [[parts per million|ppm]]<ref name=http://www.cdc.gov/Niosh/idlh/74908.html>[http://www.cdc.gov/Niosh/idlh/74908.html Documentation for Immediately Dangerous to Life or Health Concentrations (IDLHs) - 74908<!-- Bot generated title -->]</ref>.
==Footnotes==
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==References==
* Institut national de recherche et de sécurité (1997). "[http://www.inrs.fr/inrs-pub/inrs01.nsf/inrs01_ftox_view/860430FE710FCFD7C1256CE8004F67CB/$File/ft4.pdf Cyanure d'hydrogène et solutions aqueuses]". ''Fiche toxicologique n° 4'', Paris:INRS, 5pp. (PDF file, ''in French'')
==See also==
* [[Cyanide]]
* [[Hydrogen isocyanide]] (HNC)
==External links==
* [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc04/icsc0492.htm International Chemical Safety Card 0492]
* [http://www.inchem.org/documents/cicads/cicads/cicad61.htm Hydrogen cyanide and cyanides] ([[CICAD]] 61)
* [http://www.npi.gov.au/database/substance-info/profiles/29.html National Pollutant Inventory - Cyanide compounds fact sheet]
* [http://www.cdc.gov/niosh/npg/npgd0333.html NIOSH Pocket Guide to Chemical Hazards]
* [http://ecb.jrc.it/ European Chemicals Bureau]
* [http://www.hpa.org.uk/infections/topics_az/deliberate_release/chemicals/cyanide.pdf#search=%22%22dicobalt%20edetate%22%22 Department of health review]
* [http://www.osha.gov/SLTC/healthguidelines/hydrogencyanide/recognition.html OSHA: HCN Health Guidelines]
{{Chemical warfare}}
[[Category:Inorganic compounds]]
[[Category:Cyanides]]
[[Category:Hydrogen compounds]]
[[Category:Chemical weapons]]
[[Category:Fumigants]]
[[Category:Industrial processes]]
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