Hydrogen cyanide
Hydrogen cyanide (also known as prussic acid) is a chemical compound with the formula HCN and structural formula H−C≡N. 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. Large-scale applications are for the production of potassium cyanide and adiponitrile, used in mining and plastics, respectively. It is more toxic than solid cyanide compounds due to its volatile nature.
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| Names | |||
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| IUPAC name
Formonitrile | |||
| Systematic IUPAC name
Methanenitrile | |||
Other names
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| Identifiers | |||
3D model (JSmol) |
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| 3DMet | |||
| ChEBI | |||
| ChemSpider | |||
| ECHA InfoCard | 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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SMILES
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| Properties | |||
| HCN | |||
| Molar mass | 27.0253 g/mol | ||
| Appearance | Colorless liquid or gas | ||
| Odor | Almond-like | ||
| Density | 0.6876 g/cm3 | ||
| Melting point | −13.29 °C (8.08 °F; 259.86 K) | ||
| Boiling point | 26 °C (79 °F; 299 K): 4.67 | ||
| Miscible | |||
| Solubility in ethanol | Miscible | ||
| Vapor pressure | 100 kPa (25 °C): 6.94 | ||
Henry's law constant (kH) |
75 μmol Pa−1 kg−1 | ||
| Acidity (pKa) | 9.21 (in water),
12.9 (in DMSO) | ||
| Basicity (pKb) | 4.79 (cyanide anion) | ||
| Conjugate acid | Hydrocyanonium | ||
| Conjugate base | Cyanide | ||
Refractive index (nD) |
1.2675 | ||
| Viscosity | 0.183 mPa·s (25 °C): 6.231 | ||
| Structure | |||
| tetragonal (>170 K) orthorhombic (<170 K) | |||
Point group |
C∞v | ||
Molecular shape |
Linear | ||
| 2.98 D | |||
| Thermochemistry | |||
Heat capacity (C) |
35.9 J K−1 mol−1 (gas): 5.19 | ||
Std molar entropy (S⦵298) |
201.8 J K−1 mol−1 | ||
Std enthalpy of formation (ΔfH⦵298) |
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) |
4
4
2 | ||
| 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): | |||
PEL (Permissible) |
TWA 10 ppm (11 mg/m3) [skin] | ||
REL (Recommended) |
ST 4.7 ppm (5 mg/m3) [skin] | ||
IDLH (Immediate danger) |
50 ppm | ||
| 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).
Infobox references | |||
Whether hydrogen cyanide is an organic compound or not is a topic of debate among chemists, and opinions vary from author to author. Traditionally, it is considered inorganic by significant part of authors. Contrary to them, it is considered organic by other authors, because hydrogen cyanide belongs to the class of organic compounds known as nitriles which have the formula R−C≡N, where R is typically organyl group (e.g., alkyl or aryl) or hydrogen. In the case of hydrogen cyanide, the R group is hydrogen H, so the other names of hydrogen cyanide are methanenitrile and formonitrile.