Hydrogen cyanide
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Names | |||
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IUPAC name | |||
Systematic IUPAC name
Methanenitrile[3] | |||
Other names
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Identifiers | |||
3D model (
JSmol ) |
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3DMet | |||
ChEBI | |||
ChemSpider | |||
ECHA InfoCard
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100.000.747 | ||
EC Number |
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KEGG | |||
MeSH | Hydrogen+Cyanide | ||
PubChem CID
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RTECS number
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UNII | |||
UN number | 1051 | ||
CompTox Dashboard (EPA)
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Properties | |||
HCN | |||
Molar mass | 27.0253 g/mol | ||
Appearance | Colorless liquid or gas | ||
Odor | Almond-like[4] | ||
Density | 0.6876 g/cm3[5] | ||
Melting point | −13.29 °C (8.08 °F; 259.86 K)[5] | ||
Boiling point | 26 °C (79 °F; 299 K)[5]: 4.67 | ||
Miscible | |||
Solubility in ethanol | Miscible | ||
Vapor pressure | 100 kPa (25 °C)[5]: 6.94 | ||
Henry's law
constant (kH) |
75 μmol Pa−1 kg−1 | ||
Acidity (pKa) | 9.21 (in water),
12.9 (in DMSO)[6] | ||
Basicity (pKb) | 4.79 (cyanide anion) | ||
Conjugate acid
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Hydrocyanonium
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Conjugate base
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Cyanide | ||
Refractive index (nD)
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1.2675[7] | ||
Viscosity | 0.183 mPa·s (25 °C)[5]: 6.231 | ||
Structure | |||
tetragonal (>170 K) orthorhombic (<170 K)[8] | |||
C∞v | |||
Linear | |||
2.98 D | |||
Thermochemistry | |||
Heat capacity (C)
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35.9 J K−1 mol−1 (gas)[5]: 5.19 | ||
Std molar
entropy (S⦵298) |
201.8 J K−1 mol−1 | ||
Std enthalpy of (ΔfH⦵298)formation |
135.1 kJ mol−1 | ||
Hazards | |||
GHS labelling: | |||
Danger | |||
H225, H300, H310, H319, H330, H336, H370, H410 | |||
P210, P261, P305+P351+P338 | |||
NFPA 704 (fire diamond) | |||
Flash point | −17.8 °C (0.0 °F; 255.3 K) | ||
538 °C (1,000 °F; 811 K) | |||
Explosive limits
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5.6% – 40.0%[9] | ||
Lethal dose or concentration (LD, LC): | |||
LC50 (median concentration)
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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)[10] | ||
LCLo (lowest published)
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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)[10] | ||
NIOSH (US health exposure limits): | |||
PEL (Permissible)
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TWA 10 ppm (11 mg/m3) [skin][9] | ||
REL (Recommended)
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ST 4.7 ppm (5 mg/m3) [skin][9] | ||
IDLH (Immediate danger) |
50 ppm[9] | ||
Related compounds | |||
Related alkanenitriles
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Hydrogen cyanide (also known as prussic acid) is a
Whether hydrogen cyanide is an
Structure and general properties
Hydrogen cyanide is a linear molecule, with a triple bond between carbon and nitrogen. The tautomer of HCN is HNC, hydrogen isocyanide.[citation needed]
Hydrogen cyanide is weakly
HCN has a faint
Chemical properties
Hydrogen cyanide will react with alkenes under catalysis of nickel complexes. This reaction is called hydrocyanation.[15]
- RCH=CH2 + HCN → RCH2-CH2-CN
Four molecules of HCN will tetramerize into diaminomaleonitrile, which can be converted to various purines.[16]
History of discovery
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.[17] 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,[18] 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
Production and synthesis
Hydrogen cyanide forms in at least limited amounts from many combinations of hydrogen, carbon, and ammonia. Hydrogen cyanide is produced in large quantities by several processes and is a recovered waste product from the manufacture of acrylonitrile.[11] In 2006, between 500 million and 1 billion pounds (between 230,000 and 450,000 t) were produced in the US.[23]
The most important process is the
- 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.
Of lesser importance is the
- CH4 + NH3 → HCN + 3H2
This reaction is akin to steam reforming, the reaction of methane and water to give carbon monoxide and hydrogen.
In the Shawinigan Process,
In the laboratory, small amounts of HCN are produced by the addition of acids to cyanide salts of
- 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.
Hydrogen cyanide could be obtained from potassium ferricyanide and acid:
Historical methods of production
The large demand for cyanides for mining operations in the 1890s was met by
Applications
HCN is the precursor to
HCN is used globally as a
Occurrence
HCN is obtainable from
On Titan
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.[38] 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.[39] 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).[40][41] Ultraviolet radiation breaks HCN up into CN + H; however, CN is efficiently recycled back into HCN via the reaction CN + CH4 → HCN + CH3.[40]
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.[42]
In mammals
Some authors[
It has also been shown that, while stimulating
The
HCN is a constituent of tobacco smoke.[46]
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.[47] 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).[48]
In space
HCN has been detected in the interstellar medium[49] and in the atmospheres of carbon stars.[50] 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.[51] The J=1→0, J=3→2, J= 4→3, and J=10→9 pure rotational transitions have all been observed.[49][52][53]
HCN is formed in
HCN is destroyed in interstellar clouds through a number of mechanisms depending on the location in the cloud.
On 11 August 2014, astronomers released studies, using the
In February 2016, it was announced that traces of hydrogen cyanide were found in the atmosphere of the hot Super-Earth 55 Cancri e with NASA's Hubble Space Telescope.[61]
On 14 December 2023, astronomers reported the first time discovery, in the
As a poison and chemical weapon
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.[65][66] 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
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.
Perhaps its most infamous use is
During
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 sodium or potassium cyanide.[73]
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 it was quickly abandoned.[14] From the middle of the 18th century it was used in a number of poisoning murders and suicides.[74]
Hydrogen cyanide gas in air is explosive at concentrations above 5.6%.[75]
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External links
- 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 (CICAD61)
- National Pollutant Inventory: Cyanide compounds fact sheet
- NIOSH Pocket Guide to Chemical Hazards
- Department of health review
- Density of Hydrogen Cyanide gas