|Jmol interactive 3D||Image|
|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 ethanol||Miscible|
|Vapor pressure||630 mmHg (20°C)|
|75 μmol Pa−1 kg−1|
Refractive index (nD)
|Viscosity||201 μPa s|
|71.00 kJ K−1 mol−1 (at 27 °C)|
|113.01 J K−1 mol−1|
Std enthalpy of
|109.9 kJ mol−1|
Std enthalpy of
|-426.5 kJ mol−1|
EU classification (DSD)
|F+ T+ N|
|R-phrases||R12, R26/27/28, R50/53|
|S-phrases||(S1/2), S16, S36/37, S38, S45, S53, S59, S61|
|Flash point||−17.8 °C (0.0 °F; 255.3 K)|
|538 °C (1,000 °F; 811 K)|
|Explosive limits||5.6% - 40.0%|
|Lethal dose or concentration (LD, LC):|
LC50 (Median concentration)
|501 ppm (rat, 5 min)
323 ppm (mouse, 5 min)
275 ppm (rat, 15 min)
170 ppm (rat, 30 min)
160 ppm (rat, 30 min)
323 ppm (rat, 5 min)
LCLo (Lowest published)
|200 ppm (mammal, 5 min)
36 ppm (mammal, 2 hr)
107 ppm (human, 10 min)
759 ppm (rabbit, 1 min)
759 ppm (cat, 1 min)
357 ppm (human, 2 min)
179 ppm (human, 1 hr)
|US health exposure limits (NIOSH):|
|TWA 10 ppm (11 mg/m3) [skin]|
|ST 4.7 ppm (5 mg/m3) [skin]|
IDLH (Immediate danger
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Hydrogen cyanide (HCN), sometimes called prussic acid, is an organic compound with the chemical formula HCN. It is a colorless, extremely poisonous liquid that boils slightly above room temperature, at 25.6 °C (78.1 °F). HCN is produced on an industrial scale and is a highly valuable precursor to many chemical compounds ranging from polymers to pharmaceuticals.
- 1 Structure and general properties
- 2 History of discovery
- 3 Production and synthesis
- 4 Applications
- 5 Occurrence
- 6 As a poison and chemical weapon
- 7 References
- 8 External links
Structure and general properties
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.
HCN has a faint bitter almond-like odor that some people are unable to detect owing to a genetic trait. The volatile compound has been used as inhalation rodenticide 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) which had been known since 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. 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, 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 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 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. In 1815 Gay-Lussac deduced Prussic acid's chemical formula. 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.
Production and synthesis
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. In 2006 between 500 million and 1 billion pounds were produced in the US.
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:
- 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.
- CH4 + NH3 → HCN + 3H2
- 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 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.
HCN is the precursor to sodium cyanide and potassium cyanide, which are used mainly in gold and silver mining and for the electroplating of those metals. Via the intermediacy of cyanohydrins, a variety of useful organic compounds are prepared from HCN including the 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.
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. One hundred grams of crushed apple seeds can yield about 70 mg of HCN. Some millipedes release hydrogen cyanide as a defense mechanism, 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.
HCN on the young Earth
It has been postulated that carbon from a cascade of asteroids (known as the Late Heavy Bombardment), 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 neurons can produce hydrogen cyanide upon activation of their opioid receptors by endogenous or exogenous opioids. They have also shown that neuronal production of HCN activates NMDA receptors and plays a role in signal transduction between neuronal cells (neurotransmission). Moreover, increased endogenous neuronal HCN production under opioids was seemingly needed for adequate opioid analgesia, as analgesic action of opioids was attenuated by HCN scavengers. They considered endogenous HCN to be a neuromodulator.
It has also been shown that, while stimulating muscarinic cholinergic receptors in cultured pheochromocytoma cells increases HCN production, in a living organism (in vivo) muscarinic cholinergic stimulation actually decreases HCN production.
The vasodilatation, caused by sodium nitroprusside, 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 and other non-cyanogenic nitrates which do not cause blood cyanide levels to rise.
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. 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.
HCN in space
HCN has been detected in the interstellar medium. 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. The J=1→0, J=3→2, J= 4→3, and J=10→9 pure rotational transitions have all been observed.
HCN is formed in interstellar 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 (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 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 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 inside the comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON).
As a poison and chemical weapon
A hydrogen cyanide concentration of 300 mg/m3 in air will kill a human within 10–60 minutes. A hydrogen cyanide concentration of 3500 ppm (about 3200 mg/m3) will kill a human in about 1 minute. 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.
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"), it was used in the German extermination camps mass killings 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.[not specific enough to verify]
Hydrogen cyanide is commonly listed amongst chemical warfare agents known as blood agents. As a substance listed under 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. During the 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.
Under the name prussic acid, HCN has been used as a killing agent in whaling harpoons. From the mid 18th century it was used in a number of poisoning murders and suicides. 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 gas in air is explosive at concentrations over 5.6%. This is far above its toxicity level.
- "Hydrogen Cyanide - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 16 September 2004. Identification. Retrieved 2012-06-04.
- "hydrogen cyanide (CHEBI:18407)". Chemical Entities of Biological Interest. UK: European Bioinformatics Institute. 18 October 2009. Main. Retrieved 2012-06-04.
- "NIOSH Pocket Guide to Chemical Hazards #0333". National Institute for Occupational Safety and Health (NIOSH).
- Perrin, D. D. (1982). Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution (2nd ed.). Oxford: Pergamon Press.
- Patnaik, P. (2002). Handbook of Inorganic Chemicals. McGraw-Hill. ISBN 0-07-049439-8.
- NIST Chemistry WebBook
- "Hydrogen cyanide". Immediately Dangerous to Life and Health. National Institute for Occupational Safety and Health (NIOSH).
- Gail, E.; Gos, S.; Kulzer, R.; Lorösch, J.; Rubo, A.; Sauer, M. (2005), "Cyano Compounds, Inorganic", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a08_159.pub2
- "Cyanide, inability to smell". Online Mendelian Inheritance in Man. Retrieved 2010-03-31.
- Lytle, Thomas. "Poison Harpoons". Retrieved 28 October 2013.
- 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.
- 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.
- Berthollet (presented: 1787 ; published: 1789)
- 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.
- Newbold, B. T. (1999-11-01). "Claude Louis Berthollet: A Great Chemist in the French Tradition". Canadian Chemical News. Retrieved 2010-03-31.
- Gay-Lussac (1811) "Note sur l'acide prussique" (Note on prussic acid), Annales de chimie, 44: 128 - 133.
- Gay-Lussac (1815) "Recherche sur l'acide prussique" (Research on prussic acid) Annales de Chimie 95: 136-231.
- . EPA. Retrieved on 2013-01-31.
- Andrussow, L. (1935). "The catalytic oxydation of ammonia-methane-mixtures to hydrogen cyanide". Angewandte Chemie 48 (37): 593–595. doi:10.1002/ange.19350483702.
- Endter, F. (1958). "Die technische Synthese von Cyanwasserstoff aus Methan und Ammoniak ohne Zusatz von Sauerstoff". Chemie Ingenieur Technik 30 (5): 305–310. doi:10.1002/cite.330300506.
- Vetter, J. (2000). "Plant cyanogenic glycosides". Toxicon 38 (1): 11–36. doi:10.1016/S0041-0101(99)00128-2. PMID 10669009.
- Jones, D. A. (1998). "Why are so many food plants cyanogenic?". Phytochemistry 47 (2): 155–162. doi:10.1016/S0031-9422(97)00425-1. PMID 9431670.
- "Are Apple Cores Poisonous? The Naked Scientists September 2010". Retrieved 6 March 2014.
- Blum, M. S.; Woodring, J. P. (1962). "Secretion of Benzaldehyde and Hydrogen Cyanide by the Millipede Pachydesmus crassicutis (Wood)". Science 138 (3539): 512–513. Bibcode:1962Sci...138..512B. doi:10.1126/science.138.3539.512. PMID 17753947.
- 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. PMID 1650055.
- 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". Plant Physiology 116 (4): 1219–1225. doi:10.1104/pp.116.4.1219. PMC 35028. PMID 9536038.
- "Making Sense of the Chemistry That Led to Life on Earth". Retrieved 5 May 2015.
- Borowitz JL, Gunasekar PG, Isom GE. (12 Sep 1997). "Hydrogen cyanide generation by mu-opiate receptor activation: possible neuromodulatory role of endogenous cyanide.". Brain Res. 768 (1-2): 294–300. doi:10.1016/S0006-8993(97)00659-8. PMID 9369328.
- Gunasekar PG, Prabhakaran K, Li L, Zhang L, Isom GE, Borowitz JL. (May 2004). "Receptor mechanisms mediating cyanide generation in PC12 cells and rat brain.". Neurosci Res. 49 (1): 13–18. doi:10.1016/j.neures.2004.01.006. PMID 15099699.
- Smith RP, Kruszyna H. (Jan 1976). "Toxicology of some inorganic antihypertensive anions.". Fed Proc. 35 (1): 69–72. PMID 1245233.
- 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. doi:10.1007/1-4020-2522-X_8. ISBN 978-1-4020-2522-8.
- 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. doi:10.1016/S0040-4020(03)00153-4.
- Snyder, L. E.; Buhl, D. (1971). "Observations of Radio Emission from Interstellar Hydrogen Cyanide" (pdf). Astrophysical Journal 163: L47–L52. Bibcode:1971ApJ...163L..47S. doi:10.1086/180664.
- 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. Bibcode:1978Icar...34..331T. doi:10.1016/0019-1035(78)90171-9.
- 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. Bibcode:2000ApJ...543..897B. doi:10.1086/317129.
- 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. Bibcode:2003ApJ...583..446S. doi:10.1086/345099.
- Boger, G. I.; Sternberg, A. (2005). "CN and HCN in Dense Interstellar Clouds" (pdf). Astrophysical Journal 632 (1): 302–315. arXiv:astro-ph/0506535. Bibcode:2005ApJ...632..302B. doi:10.1086/432864.
- Gao, Y.; Solomon, P. M. (2004). "The Star Formation Rate and Dense Molecular Gas in Galaxies" (pdf). Astrophysical Journal 606 (1): 271–290. arXiv:astro-ph/0310339. Bibcode:2004ApJ...606..271G. doi:10.1086/382999.
- Gao, Y.; Solomon, P. M. (2004). "HCN Survey of Normal Spiral, Infrared‐luminous, and Ultraluminous Galaxies" (pdf). Astrophysical Journal Supplements 152: 63–80. arXiv:astro-ph/0310341. Bibcode:2004ApJS..152...63G. doi:10.1086/383003.
- Wu, J.; Evans, N. J. (2003). "Indications of Inflow Motions in Regions Forming Massive Stars" (pdf). Astrophysical Journal 592 (2): L79–L82. arXiv:astro-ph/0306543. Bibcode:2003ApJ...592L..79W. doi:10.1086/377679.
- Loenen, A. F. (2007). Proceedings IAU Symposium 202. Missing or empty
- Zubritsky, Elizabeth; Neal-Jones, Nancy (11 August 2014). "RELEASE 14-038 - NASA’s 3-D Study of Comets Reveals Chemical Factory at Work". NASA. Retrieved 12 August 2014.
- 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". The Astrophysical Journal 792 (1). doi:10.1088/2041-8205/792/1/L2. Retrieved 12 August 2014.
- Environmental and Health Effects. Cyanidecode.org. Retrieved on 2012-06-02.
- Dwork, D.; van Pelt, R. J. (1996). Auschwitz, 1270 to the present. Norton. p. 443. ISBN 0-393-03933-1.
- "Hydrogen Cyanide". Organisation for the Prohibition of Chemical Weapons. Retrieved 2009-01-14.
- Markus Schnedlitz (2008) Chemische Kampfstoffe: Geschichte, Eigenschaften, Wirkung. GRIN Verlag, ISBN 364023360-3, p. 13
- Poison Hand Darted Harpoons and Lances.
- The Poison Garden website http://www.thepoisongarden.co.uk/atoz/prunus_laurocerasus.htm. Retrieved 18 October 2014. Missing or empty
- "Documentation for Immediately Dangerous to Life or Health Concentrations (IDLHs) – 74908". NIOSH.
- 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