World Library  
Flag as Inappropriate
Email this Article

Hydrogen cyanide

Article Id: WHEBN0000042078
Reproduction Date:

Title: Hydrogen cyanide  
Author: World Heritage Encyclopedia
Language: English
Subject: Sodium cyanide, Acetonitrile, Chemical warfare, Jatropha curcas, Ammonia
Collection: Blood Agents, Cyanides, Fumigants, Gaseous Signaling Molecules, Hydrogen Compounds, Inorganic Compounds
Publisher: World Heritage Encyclopedia

Hydrogen cyanide

Hydrogen cyanide
Ball and stick model of hydrogen cyanide Spacefill model of hydrogen cyanide
CAS number  YesY
ChemSpider  N
EC number
UN number 1051
RTECS number MW6825000
Jmol-3D images Image 1
Molecular formula CHN
Molar mass 27.03 g mol−1
Appearance Very pale, blue, transparent liquid or colorless gas
Odor Oil of bitter almond
Density 0.687 g mL−1
Melting point −14 to −12 °C; 7 to 10 °F; 259 to 261 K
Boiling point 25.6 to 26.6 °C; 78.0 to 79.8 °F; 298.7 to 299.7 K
Solubility in water Miscible
Solubility in ethanol Miscible
kH 75 μmol Pa−1 kg−1
Acidity (pKa) 9.21[3]
Basicity (pKb) 4.79
Refractive index (nD) 1.2675 [4]
Viscosity 201 μPa s
Molecular shape Linear
Dipole moment 2.98 D
heat capacity
71.00 kJ K−1 mol−1 (at 27 °C)[5]
Std molar
113.01 J K−1 mol−1
Std enthalpy of
109.9 kJ mol−1
Std enthalpy of
-426.5 kJ mol−1
EU Index 006-006-00-X
EU classification Extremely Flammable F+ Very Toxic T+ Dangerous for the Environment (Nature) N
R-phrases R50/53
S-phrases (S1/2), S16, S36/37, S38, S45, S53, S59, S61
NFPA 704
Flash point −17.8 °C (0.0 °F; 255.4 K)
Related compounds
Related alkanenitriles
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N   YesY/N?)

Hydrogen cyanide (HCN), sometimes called prussic acid, is an

  • 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)
  • International Chemical Safety Card 0492
  • Hydrogen cyanide and cyanides (CICAD 61)
  • National Pollutant Inventory: Cyanide compounds fact sheet
  • NIOSH Pocket Guide to Chemical Hazards
  • Department of health review

External links

  1. ^ "Hydrogen Cyanide - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 16 September 2004. Identification. Retrieved 2012-06-04. 
  2. ^ "hydrogen cyanide (CHEBI:18407)". Chemical Entities of Biological Interest. UK: European Bioinformatics Institute. 18 October 2009. Main. Retrieved 2012-06-04. 
  3. ^ Perrin, D. D. (1982). Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution (2nd ed.). Oxford: Pergamon Press. 
  4. ^ Patnaik, P. (2002). Handbook of Inorganic Chemicals. McGraw-Hill.  
  5. ^ NIST Chemistry WebBook
  6. ^ a b c Gail, E.; Gos, S.; Kulzer, R.; Lorösch, J.; Rubo, A.; Sauer, M. (2005), "Cyano Compounds, Inorganic",  
  7. ^
  8. ^ "Cyanide, inability to smell".  
  9. ^ Lytle, Thomas. "Poison Harpoons". Retrieved 28 October 2013. 
  10. ^ Pierre-Joseph Macquer (presented: 1752 ; published: 1756) "Éxamen chymique de bleu de Prusse" (Chemical examination of Prussian blue), Mémoires de l'Académie royale des Sciences , pages 60-77.
  11. ^ See:
    • Carl W. Scheele (1782) "Försök, beträffande det färgande ämnet uti Berlinerblå" (Experiment concerning the coloring substance in Berlin blue), Kungliga Svenska Vetenskapsakademiens handlingar (Royal Swedish Academy of Science's Proceedings), 3: 264-275 (in Swedish).
    • Reprinted in Latin as: "De materia tingente caerulei berolinensis" in: Carl Wilhelm Scheele with Ernst Benjamin Gottlieb Hebenstreit (ed.) and Gottfried Heinrich Schäfer (trans.), Opuscula Chemica et Physica (Leipzig ("Lipsiae"), (Germany): Johann Godfried Müller, 1789), vol. 2, pages 148-174.
  12. ^ See:
    • Berthollet (presented: 1787 ; published: 1789)
    "Mémoire sur l'acide prussique" (Memoir on prussic acid), Mémoires de l'Académie Royale des Sciences, pages 148-161.
    • Reprinted in: Berthollet (1789) "Extrait d'un mémoire sur l'acide prussique" (Extract of a memoir on prussic acid), Annales de chimie 1: 30-39.
  13. ^ Newbold, B. T. (1999-11-01). "Claude Louis Berthollet: A Great Chemist in the French Tradition". Canadian Chemical News. Retrieved 2010-03-31. 
  14. ^ Gay-Lussac (1811) "Note sur l'acide prussique" (Note on prussic acid), Annales de chimie, 44: 128 - 133.
  15. ^ Gay-Lussac (1815) "Recherche sur l'acide prussique" (Research on prussic acid) Annales de Chimie 95: 136-231.
  16. ^ [1]. EPA. Retrieved on 2013-01-31.
  17. ^ Andrussow, L. (1935). "The catalytic oxydation of ammonia-methane-mixtures to hydrogen cyanide".  
  18. ^ Endter, F. (1958). "Die technische Synthese von Cyanwasserstoff aus Methan und Ammoniak ohne Zusatz von Sauerstoff". Chemie Ingenieur Technik 30 (5): 305–310.  
  19. ^ Vetter, J. (2000). "Plant cyanogenic glycosides". Toxicon 38 (1): 11–36.  
  20. ^ Jones, D. A. (1998). "Why are so many food plants cyanogenic?".  
  21. ^ "Are Apple Cores Poisonous? The Naked Scientists September 2010". Retrieved 6 March 2014. 
  22. ^ Blum, M. S.; Woodring, J. P. (1962). "Secretion of Benzaldehyde and Hydrogen Cyanide by the Millipede Pachydesmus crassicutis (Wood)".  
  23. ^ Aregheore, E. M.; Agunbiade, O. O. (1991). "The toxic effects of cassava (manihot esculenta grantz) diets on humans: a review". Veterinary and Human Toxicology 33 (3): 274–275.  
  24. ^ White, W. L. B.; Arias-Garzon, D. I.; McMahon, J. M.; Sayre, R. T. (1998). "Cyanogenesis in Cassava, The Role of Hydroxynitrile Lyase in Root Cyanide Production".  
  25. ^ Matthews, C. N. (2004). "The HCN World: Establishing Protein - Nucleic Acid Life via Hydrogen Cyanide Polymers". Origins: Genesis, Evolution and Diversity of Life. Cellular Origin and Life in Extreme Habitats and Astrobiology 6. pp. 121–135.  
  26. ^ Al-Azmi, A.; Elassar, A.-Z. A.; Booth, B. L. (2003). "The Chemistry of Diaminomaleonitrile and its Utility in Heterocyclic Synthesis". Tetrahedron 59 (16): 2749–2763.  
  27. ^ a b Snyder, L. E.; Buhl, D. (1971). "Observations of Radio Emission from Interstellar Hydrogen Cyanide" (pdf). Astrophysical Journal 163: L47–L52.  
  28. ^ Treffers, R.; Larson, H. P.; Fink, U.; Gautier, T. N. (1978). "Upper limits to trace constituents in Jupiter's atmosphere from an analysis of its 5-μm spectrum". Icarus 34 (2): 331–343.  
  29. ^ Bieging, J. H.; Shaked, S.; Gensheimer, P. D. (2000). "Submillimeter‐ and Millimeter‐Wavelength Observations of SiO and HCN in Circumstellar Envelopes of AGB Stars" (pdf). Astrophysical Journal 543 (2): 897–921.  
  30. ^ Schilke, P.; Menten, K. M. (2003). "Detection of a Second, Strong Sub-millimeter HCN Laser Line toward Carbon Stars" (pdf). Astrophysical Journal 583 (1): 446–450.  
  31. ^ a b Boger, G. I.; Sternberg, A. (2005). "CN and HCN in Dense Interstellar Clouds" (pdf). Astrophysical Journal 632 (1): 302–315.  
  32. ^ Gao, Y.; Solomon, P. M. (2004). "The Star Formation Rate and Dense Molecular Gas in Galaxies" (pdf). Astrophysical Journal 606 (1): 271–290.  
  33. ^ Gao, Y.; Solomon, P. M. (2004). "HCN Survey of Normal Spiral, Infrared‐luminous, and Ultraluminous Galaxies" (pdf). Astrophysical Journal Supplements 152: 63–80.  
  34. ^ Wu, J.; Evans, N. J. (2003). "Indications of Inflow Motions in Regions Forming Massive Stars" (pdf). Astrophysical Journal 592 (2): L79–L82.  
  35. ^ Loenen, A. F. (2007). Proceedings IAU Symposium 202. 
  36. ^ Zubritsky, Elizabeth; Neal-Jones, Nancy (11 August 2014). "RELEASE 14-038 - NASA’s 3-D Study of Comets Reveals Chemical Factory at Work".  
  37. ^ Cordiner, M.A. et al. (11 August 2014). "Mapping the Release of Volatiles in the Inner Comae of Comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON) Using the Atacama Large Millimeter/Submillimeter Array".  
  38. ^ a b Environmental and Health Effects. Retrieved on 2012-06-02.
  39. ^ Dwork, D.;  
  40. ^ "Hydrogen Cyanide". Organisation for the Prohibition of Chemical Weapons. Retrieved 2009-01-14. 
  41. ^ Markus Schnedlitz (2008) Chemische Kampfstoffe: Geschichte, Eigenschaften, Wirkung. GRIN Verlag, ISBN 364023360-3, p. 13
  42. ^ Poison Hand Darted Harpoons and Lances.
  43. ^ The Poison Garden website . Retrieved 18 October 2014. 
  44. ^ "Documentation for Immediately Dangerous to Life or Health Concentrations (IDLHs) – 74908". NIOSH. 


Hydrogen cyanide gas in air is explosive at concentrations over 5.6%.[44] This is far above its toxicity level.

Under the name prussic acid, HCN has been used as a killing agent in whaling harpoons.[42] From the mid 18th century it was used in a number of poisoning murders and suicides.[43] Cyanide has also been used in major occurrences of suicide in the 20th century, including the deaths of over 900 people at Jonestown and the mass suicides in 1945 Nazi Germany.

Hydrogen cyanide is commonly listed amongst First World War, the United States and Italy used hydrogen cyanide against the Central Powers in 1918. France had used it in combat already in 1916, but this proved to be ineffective due to physical conditions.[41]

Hydrogen cyanide has been absorbed into a carrier for use as a pesticide. Under IG Farben's brand name Zyklon B (German >Cyclone B, with the B standing for Blausäure - "Prussic Acid"),[39] it was used in the German concentration camp mass killing during World War II. The same product is currently made in the Czech Republic under the trademark "Uragan D2". Hydrogen cyanide was also the agent employed in judicial execution in some U.S. states, where it was produced during the execution by the action of sulfuric acid on an egg-sized mass of potassium cyanide.

A hydrogen cyanide concentration of 300 mg/m3 in air will kill a human within 10–60 minutes.[38] A hydrogen cyanide concentration of 3500 ppm (about 3200 mg/m3) will kill a human in about 1 minute.[38] The toxicity is caused by the cyanide ion, which halts cellular respiration by acting as a non-competitive inhibitor for an enzyme in mitochondria called cytochrome c oxidase. Specifically CN- binds to Fe in the heme subunit in cytochromes, interrupting electron transfer.

As a poison and chemical weapon

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 inside the comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON).[36][37]

HCN is destroyed in interstellar clouds through a number of mechanisms depending on the location in the cloud.[31] In photon-dominated regions (PDRs), photodissociation dominates, producing CN (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[32][33] and as a tracer of stellar inflow in high-mass star-forming regions.[34] Further, the HNC/HCN ratio has been shown to be an excellent method for distinguishing between PDRs and X-ray-dominated regions (XDRs).[35]

HCN is formed in interstellar clouds through one of two major pathways:[31] 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 (HNC).

HCN has been detected in the interstellar medium.[27] 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 observed from ground-based telescopes through a number of atmospheric windows.[28] The J=1→0, J=3→2, J= 4→3, and J=10→9 pure rotational transitions have all been observed.[27][29][30]

HCN in space

[26] Hydrogen cyanide has been discussed as a precursor to amino acids and nucleic acids. For example, HCN is proposed to have played a part in the

HCN and the origin of life

HCN is obtainable from fruits that have a pit, such as cherries, apricots, apples, and bitter almonds, from which almond oil and flavoring are made. Many of these pits contain small amounts of cyanohydrins such as mandelonitrile and amygdalin, which slowly release hydrogen cyanide.[19][20] One hundred grams of crushed apple seeds can yield about 70 mg of HCN.[21] Some millipedes release hydrogen cyanide as a defense mechanism,[22] as do certain insects, such as some burnet moths. Hydrogen cyanide is contained in the exhaust of vehicles, in tobacco and wood smoke, and in smoke from burning nitrogen-containing plastics. So-called "bitter" roots of the cassava plant may contain up to 1 gram of HCN per kilogram.[23][24]


HCN is the precursor to monomer methyl methacrylate, from acetone, the amino acid methionine, via the Strecker synthesis, and the chelating agents EDTA and NTA. Via the hydrocyanation process, HCN is added to butadiene to give adiponitrile, a precursor to Nylon 66.[6]


The demand for cyanides for mining operations in the 1890s was met by 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.

Historical methods of production

This reaction is sometimes the basis of accidental poisonings because the acid converts a nonvolatile cyanide salt into the gaseous HCN.

H+ + NaCN → HCN + Na+

In the Shawinigan Process, hydrocarbons, e.g. 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:

This reaction is akin to steam reforming, the reaction of methane and water to give carbon monoxide and hydrogen.

CH4 + NH3 → HCN + 3H2

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:[18]

The energy needed for the reaction is provided by the partial oxidation of methane and ammonia.

2 CH4 + 2 NH3 + 3 O2 → 2 HCN + 6 H2O

The most important process is the Andrussow oxidation invented by Leonid Andrussow at IG Farben in which methane and ammonia react in the presence of oxygen at about 1200 °C over a platinum catalyst:[17]

Hydrogen cyanide forms in at least limited amounts from many combinations of hydrogen, carbon, and 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.[6] In 2006 between 500 million and 1 billion pounds were produced in the US.[16]

Production and synthesis

In 1787 the French chemist Claude Louis Berthollet showed that Prussic acid did not contain oxygen,[12] an important contribution to acid theory, which had thitherto postulated that acids must contain oxygen[13] (hence the name of oxygen itself, which is derived from Greek elements that mean "acid-former" and are likewise calqued into German as Sauerstoff). In 1811 Joseph Louis Gay-Lussac prepared pure, liquified hydrogen cyanide.[14] In 1815 Gay-Lussac deduced Prussic acid's chemical formula.[15] The radical cyanide in hydrogen cyanide was given its name from cyan, not only an English word for a shade of blue but the Greek word for blue (Ancient Greek: κυανοῦς), again owing to its derivation from Prussian blue.

Hydrogen cyanide was first isolated from a blue pigment (Prussian blue) which had been known from 1704 but whose structure was unknown. It is now known to be a coordination polymer with a complex structure and an empirical formula of hydrated ferric ferrocyanide. In 1752, the French chemist Pierre Macquer made the important step of showing that Prussian blue could be converted to iron oxide plus a volatile component and that these could be used to reconstitute it.[10] The new component was what we now know as hydrogen cyanide. Following Macquer's lead, it was first prepared from Prussian blue by the Swedish chemist Carl Wilhelm Scheele in 1782,[11] 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.

The red colored ferricyanide ion, one component of Prussian blue

History of discovery

HCN has a faint bitter almond-like odor that some people are unable to detect owing to a genetic trait.[8] The volatile compound has been used as inhalation rodenticide and human poison, as well as for killing whales.[9] Cyanide ions interfere with iron-containing respiratory enzymes.

Hydrogen cyanide is weakly acidic with a pKa of 9.2. It partially ionizes in water solution to give the cyanide anion, CN. A solution of hydrogen cyanide in water, represented as HCN, is called hydrocyanic acid. The salts of the cyanide anion are known as cyanides.

Hydrogen cyanide is a linear molecule, with a triple bond between carbon and nitrogen. A minor tautomer of HCN is HNC, hydrogen isocyanide.

Structure and general properties


  • Structure and general properties 1
  • History of discovery 2
  • Production and synthesis 3
    • Historical methods of production 3.1
  • Applications 4
  • Occurrence 5
    • HCN and the origin of life 5.1
    • HCN in space 5.2
  • As a poison and chemical weapon 6
  • References 7
  • External links 8

to pharmaceuticals. polymers HCN is produced on an industrial scale and is a highly valuable precursor to many chemical compounds ranging from [7], at 25.6 °C (78.1 °F).room temperature slightly above boils liquid that poisonous, extremely colorless HCN. It is a chemical formula with the [6]

This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from World eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.