Hydrogen Cyanide

Title: Hydrogen Cyanide
CAS Registry Number: 74-90-8
CAS Name: Hydrocyanic acid
Additional Names: prussic acid
Molecular Formula: CHN
Molecular Weight: 27.03
Percent Composition: C 44.43%, H 3.73%, N 51.82%
Line Formula: HCN
Literature References: Prepd on a large scale by the catalytic oxidation of ammonia-methane mixtures (Andrussow Process): see Andrussow, Angew. Chem. 48, 593 (1935); Maffezzoni, Chim. Ind. (Milan) 34, 460 (1952); Faith, Keyes & Clark's Industrial Chemicals, F. A. Lowenheim, M. K. Moran, Ed. (Wiley-Interscience, New York, 4th ed., 1975) pp 482-486. Prepd in the lab by acidifying NaCN or K4[Fe(CN)6]: Glemser in Handbook of Preparative Inorganic Chemistry vol. 1, G. Brauer, Ed. (Academic Press, New York, 2nd ed., 1963) pp 658-660. Review of toxicology and human exposure: Toxicological Profile for Cyanide (PB98-101207, 1997) 291 pp.
Properties: Colorless gas or liquid; characteristic odor. Burns in air with a blue flame. Flammable. Intensely poisonous even when mixed with air. Must be handled by specially trained experts. mp -13.4°. bp 25.6°. d(gas) 0.941 (air = 1); d(liq) 0.687. Very weakly acid (does not redden litmus). Miscible with water, alc; slightly sol in ether. LC50 in rats, mice, dogs: 544 ppm (5 min), 169 ppm (30 min), 300 ppm (3 min) by inhalation, K. C. Back et al., Reclassification of Materials Listed as Transportation Health Hazards (TSA-20-72-3; PB214-270, 1972).
Melting point: mp -13.4°
Boiling point: bp 25.6°
Density: d(gas) 0.941 (air = 1); d(liq) 0.687
Toxicity data: LC50 in rats, mice, dogs: 544 ppm (5 min), 169 ppm (30 min), 300 ppm (3 min) by inhalation, K. C. Back et al., Reclassification of Materials Listed as Transportation Health Hazards (TSA-20-72-3; PB214-270, 1972)
CAUTION: Potential symptoms of acute overexposure are asphyxia; lassitude, headache, confusion; nausea, vomiting; increased rate and depth of respiration, or slow and gasping respiration. See NIOSH Pocket Guide to Chemical Hazards (PB2003-100121, 2003) p 168; Patty's Industrial Hygiene and Toxicology vol. 2D, G. D. Clayton, F. E. Clayton, Eds. (Wiley-Interscience, NewYork, 4th ed., 1994) pp 3119-3127.
Use: Compressed gas as rodenticide, and insect fumigant.
Hydrogen Fluoride Hydrogen Iodide Hydrogen Selenide Hydrogen Sulfide Hydrogen Telluride

Hydrogen cyanide
Ball and stick model of hydrogen cyanide Spacefill model of hydrogen cyanide
CAS number 74-90-8 YesY
PubChem 768
ChemSpider 748 N
EC number 200-821-6
UN number 1051
KEGG C01326 N
MeSH Hydrogen+Cyanide
RTECS number MW6825000
3DMet B00275
Jmol-3D images Image 1
Molecular formula CHN
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 water Miscible
Solubility in ethanol Miscible
kH 75 μmol Pa−1 kg−1
Acidity (pKa) 9.21[3]
Basicity (pKb) 4.79
Refractive index (nD) 1.2675 [4]
Viscosity 201 μPa s
Molecular shape Linear
Dipole moment 2.98 D
heat capacity C
71.00 kJ K−1 mol−1 (at 27 °C)[5]
Std molar
entropy So298
113.01 J K−1 mol−1
Std enthalpy of
formation ΔfHo298
109.9 kJ mol−1
Std enthalpy of
combustion ΔcHo298
-426.5 kJ mol−1
EU Index 006-006-00-X
EU classification Flammable F+ Very Toxic T+ Dangerous for the Environment (Nature) N
R-phrases R12, R26/27/28, R50/53
S-phrases (S1/2), S16, S36/37, S38, S45, S53, S59, S61
NFPA 704
NFPA 704.svg
Flash point −17.8 °C; 0.0 °F; 255.3 K
Autoignition temperature 538 °C; 1,000 °F; 811 K
Related compounds
Related alkanenitriles
  • Hydrogen isocyanide
  • Isocyanic acid
  • Thiocyanic acid
  • Cyanogen iodide
  • Cyanogen bromide
  • Cyanogen chloride
  • Cyanogen fluoride
  • Acetonitrile
  • Aminoacetonitrile
  • Glycolonitrile
  • Cyanogen
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Hydrogen cyanide (HCN), sometimes called prussic acid, is an inorganic compound[6] with chemical formula HCN. It is a colorless, extremely poisonous liquid that boils slightly above room temperature, at 25.6 °C (78.1 °F).[7] HCN is produced on an industrial scale and is a highly valuable precursor to many chemical compounds ranging from polymers to pharmaceuticals.