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 boils slightly above room temperature, at 25.6 °C (78.1 °F). HCN is produced on an industrial scale and is a highly valued precursor to many chemical compounds ranging from polymers to pharmaceuticals.
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||27.0253 g/mol|
|Appearance||Colorless liquid or gas|
|Odor||Oil of bitter almond|
|Melting point||−13.29 °C (8.08 °F; 259.86 K)|
|Boiling point||26 °C (79 °F; 299 K):4.67|
|Solubility in ethanol||Miscible|
|Vapor pressure||100 kPa (25 °C):6.94|
|75 μmol Pa−1 kg−1|
|Acidity (pKa)||9.21 (in water),
12.9 (in DMSO) 
|Basicity (pKb)||4.79 (cyanide anion)|
Refractive index (nD)
|Viscosity||0.183 mPa·s (25 °C):6.231|
Heat capacity (C)
|35.9 J K−1 mol−1 (gas):5.19|
|201.8 J K−1 mol−1|
Std enthalpy of
|135.1 kJ mol−1|
|GHS Signal word||Danger|
|H225, H300, H310, H319, H330, H336, H370, H400, H410|
|P210, P261, P305+351+338|
|NFPA 704 (fire diamond)|
|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)
|NIOSH (US health exposure limits):|
|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 ?)(|
Structure and general propertiesEdit
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 recessive 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 discoveryEdit
Hydrogen cyanide was first isolated from a blue pigment (Prussian blue) which had been known since 1706, 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 an iron oxide plus a volatile component and that these could be used to reconstitute it. The new component was what is now known as hydrogen cyanide. Following Macquer's lead, it was first prepared from Prussian blue by the Swedish chemist Carl Wilhelm Scheele 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: κύανος), again owing to its derivation from Prussian blue.
Production and synthesisEdit
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 (between 230,000 and 450,000 t) 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 1,200 °C (2,190 °F) 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 productionEdit
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-6,6.
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, such as Harpaphe haydeniana, Desmoxytes purpurosea, and Apheloria release hydrogen cyanide as a defense mechanism, as do certain insects, such as burnet moths and the larvae of Paropsisterna eucalyptus. Hydrogen cyanide is contained in the exhaust of vehicles, and in smoke from burning nitrogen-containing plastics. So-called "bitter" roots of the cassava plant may contain up to 1 gram of HCN per kilogram.
HCN on TitanEdit
HCN has been measured in Titan's atmosphere by four instruments on the Cassini space probe, one instrument on Voyager, and one instrument on Earth. One of these measurements was in situ, where the Cassini spacecraft dipped between 1,000 and 1,100 km (620 and 680 mi) above Titan's surface to collect atmospheric gas for mass spectrometry analysis. HCN initially forms in Titan's atmosphere through the reaction of photochemically produced methane and nitrogen radicals which proceed through the H2CN intermediate, e.g., (CH3 + N → H2CN + H → HCN + H2). Ultraviolet radiation breaks HCN up into CN + H; however, CN is efficiently recycled back into HCN via the reaction CN + CH4 → HCN + CH3.
HCN on the young EarthEdit
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 mammalsEdit
Some authors[who?] 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 lifeEdit
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 (e.g. Adenine).
HCN in spaceEdit
HCN has been detected in the interstellar medium and in the atmospheres of carbon stars. 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 weaponEdit
In World War I, hydrogen cyanide was used by the French from 1916 as a chemical weapon against the Central Powers, and by the United States and Italy in 1918. It was not found to be effective enough due to weather conditions. The gas is lighter than air and rapidly disperses up into the atmosphere. Rapid dilution made its use in the field impractical. In contrast, denser agents such as phosgene or chlorine tended to remain at ground level and sank into the trenches of the Western Front's battlefields. Compared to such agents hydrogen cyanide had to be present in higher concentrations in order to be fatal.
A hydrogen cyanide concentration of 100–200 ppm in breathing air will kill a human within 10 to 60 minutes. A hydrogen cyanide concentration of 2000 ppm (about 2380 mg/m3) will kill a human in about one minute. The toxic effect is caused by the action of the cyanide ion, which halts cellular respiration. It acts as a non-competitive inhibitor for an enzyme in mitochondria called cytochrome c oxidase. As such, hydrogen cyanide is commonly listed among chemical weapons as a blood agent.
The Chemical Weapons Convention lists it under Schedule 3 as a potential weapon which has large-scale industrial uses. Signatory countries must declare manufacturing plants that produce more than 30 metric tons per year, and allow inspection by the Organisation for the Prohibition of Chemical Weapons.
Carrier absorbed hydrogen cyanide can find use as a pesticide. Perhaps the most infamous of these is Zyklon B (German: Cyclone B, with the B standing for Blausäure – prussic acid; also, to distinguish it from an earlier product later known as Zyklon A), it was used in Nazi German extermination camps during World War II to kill en masse as part of their Final Solution genocide program. Hydrogen cyanide was also used in the camps for delousing clothing in attempts to eradicate diseases carried by lice and other parasites. One of the original Czech producers continued making Zyklon B under the trademark "Uragan D2" until recently.[when?]
Under the name prussic acid, HCN has been used as a killing agent in whaling harpoons, although it proved quite dangerous to the crew deploying it, and was quickly abandoned. From the middle of the 18th century it was used in a number of poisoning murders and suicides.
Hydrogen cyanide gas in air is explosive at concentrations above 5.6%. This concentration is far above a toxic level.
- "Hydrogen Cyanide – Compound Summary". PubChem Compound. United States: 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.
- Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. ISBN 978-1439855119.
- Evans DA. "pKa's of Inorganic and Oxo-Acids" (PDF). Retrieved June 19, 2020.
- Patnaik P (2002). Handbook of Inorganic Chemicals. McGraw-Hill. ISBN 978-0-07-049439-8.
- NIOSH Pocket Guide to Chemical Hazards. "#0333". National Institute for Occupational Safety and Health (NIOSH).
- "Hydrogen cyanide". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
- Gail, E.; Gos, S.; Kulzer, R.; Lorösch, J.; Rubo, A.; Sauer, M. "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 T. "Poison Harpoons". Whalecraft.net. Archived from the original on 2019-02-15.
- Macquer PJ (1756). "Éxamen chymique de bleu de Prusse" [Chemical examination of Prussian blue]. Mémoires de l'Académie royale des Sciences (in French): 60–77.
- Scheele CW (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 (in Swedish). 3: 264–275.
Reprinted in Latin as: Scheele CW, Hebenstreit EB, eds. (1789). "De materia tingente caerulei berolinensis". Opuscula Chemica et Physica [The dark matter tingente caerulei berolinensis] (in Latin). 2. Translated by Schäfer GH. (Leipzig ("Lipsiae") (Germany): Johann Godfried Müller. pp. 148–174.
- Berthollet CL (1789). "Mémoire sur l'acide prussique" [Memoir on prussic acid]. Mémoires de l'Académie Royale des Sciences (in French): 148–161.
Reprinted in: Berthollet CL (1789). "Extrait d'un mémoire sur l'acide prussique" [Extract of a memoir on prussic acid]. Annales de Chimie. 1: 30–39.
- Newbold BT (1999-11-01). "Claude Louis Berthollet: A Great Chemist in the French Tradition". Canadian Chemical News. Retrieved 2010-03-31.
- Gay-Lussac JL (1811). "Note sur l'acide prussique" [Note on prussic acid]. Annales de Chimie. 44: 128–133.
- Gay-Lussac JL (1815). "Recherche sur l'acide prussique" [Research on prussic acid]. Annales de Chimie. 95: 136–231.
- Non-confidential 2006 IUR Records by Chemical, including Manufacturing, Processing and Use Information. 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 (January 2000). "Plant cyanogenic glycosides". Toxicon. 38 (1): 11–36. doi:10.1016/S0041-0101(99)00128-2. PMID 10669009.
- Jones DA (January 1998). "Why are so many food plants cyanogenic?". Phytochemistry. 47 (2): 155–62. doi:10.1016/S0031-9422(97)00425-1. PMID 9431670.
- "Are Apple Cores Poisonous?". The Naked Scientists. 26 September 2010. Archived from the original on 6 March 2014. Retrieved 6 March 2014.
- Blum MS, Woodring JP (October 1962). "Secretion of Benzaldehyde and Hydrogen Cyanide by the Millipede Pachydesmus crassicutis (Wood)". Science. 138 (3539): 512–3. Bibcode:1962Sci...138..512B. doi:10.1126/science.138.3539.512. PMID 17753947. S2CID 40193390.
- Zagrobelny M, de Castro ÉC, Møller BL, Bak S (May 2018). "Cyanogenesis in Arthropods: From Chemical Warfare to Nuptial Gifts". Insects. 9 (2): 51. doi:10.3390/insects9020051. PMC 6023451. PMID 29751568.
- Aregheore EM, Agunbiade OO (June 1991). "The toxic effects of cassava (manihot esculenta grantz) diets on humans: a review". Veterinary and Human Toxicology. 33 (3): 274–5. PMID 1650055.
- White WL, Arias-Garzon DI, McMahon JM, Sayre RT (April 1998). "Cyanogenesis in cassava. The role of hydroxynitrile lyase in root cyanide production". Plant Physiology. 116 (4): 1219–25. doi:10.1104/pp.116.4.1219. PMC 35028. PMID 9536038.
- Loison JC, Hébrard E, Dobrijevic M, Hickson KM, Caralp F, Hue V, et al. (February 2015). "The neutral photochemistry of nitriles, amines and imines in the atmosphere of Titan". Icarus. 247: 218–247. Bibcode:2015Icar..247..218L. doi:10.1016/j.icarus.2014.09.039.
- Magee BA, Waite JH, Mandt KE, Westlake J, Bell J, Gell DA (December 2009). "INMS-derived composition of Titan's upper atmosphere: Analysis methods and model comparison". Planetary and Space Science. 57 (14–15): 1895–1916. Bibcode:2009P&SS...57.1895M. doi:10.1016/j.pss.2009.06.016.
- Pearce BK, Molaverdikhani K, Pudritz RE, Henning T, Hébrard E (2020). "HCN Production in Titan's Atmosphere: Coupling Quantum Chemistry and Disequilibrium Atmospheric Modeling". Astrophysical Journal. 901 (2): 110. arXiv:2008.04312. Bibcode:2020ApJ...901..110P. doi:10.3847/1538-4357/abae5c. S2CID 221095540.
- Pearce BK, Ayers PW, Pudritz RE (March 2019). "A Consistent Reduced Network for HCN Chemistry in Early Earth and Titan Atmospheres: Quantum Calculations of Reaction Rate Coefficients". The Journal of Physical Chemistry A. 123 (9): 1861–1873. arXiv:1902.05574. Bibcode:2019JPCA..123.1861P. doi:10.1021/acs.jpca.8b11323. PMID 30721064. S2CID 73442008.
- Wade N (2015-05-04). "Making Sense of the Chemistry That Led to Life on Earth". The New York Times. Retrieved 5 May 2015.
- Borowitz JL, Gunasekar PG, Isom GE (September 1997). "Hydrogen cyanide generation by mu-opiate receptor activation: possible neuromodulatory role of endogenous cyanide". Brain Research. 768 (1–2): 294–300. doi:10.1016/S0006-8993(97)00659-8. PMID 9369328. S2CID 12277593.
- 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". Neuroscience Research. 49 (1): 13–8. doi:10.1016/j.neures.2004.01.006. PMID 15099699. S2CID 29850349.
- Smith RP, Kruszyna H (January 1976). "Toxicology of some inorganic antihypertensive anions". Federation Proceedings. 35 (1): 69–72. PMID 1245233.
- Talhout R, Schulz T, Florek E, van Benthem J, Wester P, Opperhuizen A (February 2011). "Hazardous compounds in tobacco smoke". International Journal of Environmental Research and Public Health. 8 (2): 613–28. doi:10.3390/ijerph8020613. PMC 3084482. PMID 21556207.
- Matthews CN (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 AZ, Booth BL (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 LE, Buhl D (1971). "Observations of Radio Emission from Interstellar Hydrogen Cyanide". Astrophysical Journal. 163: L47–L52. Bibcode:1971ApJ...163L..47S. doi:10.1086/180664.
- Jørgensen UG (1997). "Cool Star Models". In van Dishoeck EF (ed.). Molecules in Astrophysics: Probes and Processes. International Astronomical Union Symposia. Molecules in Astrophysics: Probes and Processes. 178. Springer Science & Business Media. p. 446. ISBN 978-0792345381.
- Treffers RR, Larson HP, Fink U, Gautier TN (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 JH, Shaked S, Gensheimer PD (2000). "Submillimeter‐ and Millimeter‐Wavelength Observations of SiO and HCN in Circumstellar Envelopes of AGB Stars". Astrophysical Journal. 543 (2): 897–921. Bibcode:2000ApJ...543..897B. doi:10.1086/317129.
- Schilke P, Menten KM (2003). "Detection of a Second, Strong Sub-millimeter HCN Laser Line toward Carbon Stars". Astrophysical Journal. 583 (1): 446–450. Bibcode:2003ApJ...583..446S. doi:10.1086/345099.
- Boger GI, Sternberg A (2005). "CN and HCN in Dense Interstellar Clouds". Astrophysical Journal. 632 (1): 302–315. arXiv:astro-ph/0506535. Bibcode:2005ApJ...632..302B. doi:10.1086/432864. S2CID 118958200.
- Gao Y, Solomon PM (2004). "The Star Formation Rate and Dense Molecular Gas in Galaxies". Astrophysical Journal. 606 (1): 271–290. arXiv:astro-ph/0310339. Bibcode:2004ApJ...606..271G. doi:10.1086/382999. S2CID 11335358.
- Gao Y, olomon PM (2004). "HCN Survey of Normal Spiral, Infrared‐luminous, and Ultraluminous Galaxies". Astrophysical Journal Supplement Series. 152 (1): 63–80. arXiv:astro-ph/0310341. Bibcode:2004ApJS..152...63G. doi:10.1086/383003. S2CID 9135663.
- Wu J, Evans NJ (2003). "Indications of Inflow Motions in Regions Forming Massive Stars". Astrophysical Journal. 592 (2): L79–L82. arXiv:astro-ph/0306543. Bibcode:2003ApJ...592L..79W. doi:10.1086/377679. S2CID 8016228.
- Loenen AF (2007). "Molecular properties of (U)LIRGs: CO, HCN, HNC and HCO+". Proceedings IAU Symposium. 242: 462–466. arXiv:0709.3423. Bibcode:2007IAUS..242..462L. doi:10.1017/S1743921307013609. S2CID 14398456.
- Zubritsky E, Neal-Jones N (11 August 2014). "RELEASE 14-038 – NASA's 3-D Study of Comets Reveals Chemical Factory at Work". NASA. Retrieved 12 August 2014.
- Cordiner MA, Remijan AJ, Boissier J, Milam SN, Mumma MJ, Charnley SB, 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): L2. arXiv:1408.2458. Bibcode:2014ApJ...792L...2C. doi:10.1088/2041-8205/792/1/L2. S2CID 26277035.
- "First detection of super-earth atmosphere". ESA/Hubble Information Centre. February 16, 2016.
- Schnedlitz, Markus (2008) Chemische Kampfstoffe: Geschichte, Eigenschaften, Wirkung. GRIN Verlag. p. 13. ISBN 364023360-3.
- Weapons of War - Poison Gas. firstworldwar.com
- Environmental and Health Effects. Cyanidecode.org. Retrieved on 2012-06-02.
- "Hydrogen Cyanide". Organisation for the Prohibition of Chemical Weapons. Retrieved 2009-01-14.
- Dwork D, van Pelt RJ (1996). Auschwitz, 1270 to the present. Norton. p. 443. ISBN 978-0-393-03933-7.
- "BLUE FUME". Chemical Factory Draslovka a.s. Retrieved 2020-07-06.
- "The Poison Garden website". Retrieved 18 October 2014.
- "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
- Density of Hydrogen Cyanide gas