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Prussic acid

Hydrogen cyanide
Hydrogen-cyanide-2D.svg
Ball and stick model of hydrogen cyanide
Spacefill model of hydrogen cyanide
Names
IUPAC name
  • Formonitrile(substitutive)
  • Hydridonitridocarbon(additive)
Other names
  • Formic anammonide
  • Hydrocyanic acid
  • Prussic acid
  • Methanenitrile
Identifiers
74-90-8 YesY
3D model (Jmol) Interactive image
3DMet B00275
ChEBI CHEBI:18407 N
ChemSpider 748 N
ECHA InfoCard 100.000.747
EC Number 200-821-6
KEGG C01326 N
MeSH Hydrogen+Cyanide
PubChem 768
RTECS number MW6825000
UNII 2WTB3V159F YesY
UN number 1051
Properties
HCN
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
Miscible
Solubility in ethanol Miscible
Vapor pressure 630 mmHg (20 °C)
75 μmol Pa−1 kg−1
Acidity (pKa) 9.21
Basicity (pKb) 4.79
1.2675
Viscosity 201 μPa s
Structure
C∞v
Linear
2.98 D
Thermochemistry
71.00 kJ K−1 mol−1 (at 27 °C)
113.01 J K−1 mol−1
109.9 kJ mol−1
-426.5 kJ mol−1
Hazards
GHS pictograms The flame pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The skull-and-crossbones pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The exclamation-mark pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word DANGER
H225, H319, H336
P210, P261, P305+351+338
Extremely 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
Flammability code 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g., propane Health code 4: Very short exposure could cause death or major residual injury. E.g., VX gas Reactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorus Special hazards (white): no codeNFPA 704 four-colored 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):
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)
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)
US health exposure limits (NIOSH):
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
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YesYN ?)
Infobox references

Hydrogen cyanide (HCN), sometimes called prussic acid, is an organic 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 valuable precursor to many chemical compounds ranging from polymers to pharmaceuticals.

Hydrogen cyanide is a linear molecule, with a triple bond between carbon and nitrogen. A minor tautomer of HCN is HNC, hydrogen isocyanide.

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.


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