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
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| Systematic IUPAC name
Hydrogen cyanide (gas form) Hydrocyanic acid (aqueous) | |||
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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| 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) | |||
| C∞v | |||
| 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) | |||
| 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 | |||
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