Prussic acid

Hydrogen cyanide

Names
IUPAC name Formonitrile(substitutive) Hydridonitridocarbon(additive)
Other names Formic anammonide Hydrocyanic acid Prussic acid Methanenitrile
Identifiers
CAS Number	74-90-8 Y
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 Y
UN number	1051
InChI InChI=1S/CHN/c1-2/h1H N Key: LELOWRISYMNNSU-UHFFFAOYSA-N N
SMILES C#N
Properties
Chemical formula	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
Solubility in water	Miscible
Solubility in ethanol	Miscible
Vapor pressure	630 mmHg (20 °C)
Henry's law constant (kH)	75 μmol Pa−1 kg−1
Acidity (pKa)	9.21
Basicity (pKb)	4.79
Refractive index (nD)	1.2675
Viscosity	201 μPa s
Structure
Point group	C∞v
Molecular shape	Linear
Dipole moment	2.98 D
Thermochemistry
Specific heat capacity (C)	71.00 kJ K−1 mol−1 (at 27 °C)
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
Hazards
GHS pictograms
GHS signal word	DANGER
GHS hazard statements	H225, H319, H336
GHS precautionary statements	P210, P261, P305+351+338
EU classification (DSD)	F+ T+ N
R-phrases	R12, R26/27/28, R50/53
S-phrases	(S1/2), S16, S36/37, S38, S45, S53, S59, S61
NFPA 704	4 4 2
Flash point	−17.8 °C (0.0 °F; 255.3 K)
Autoignition temperature	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)
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	Hydrogen isocyanide Isocyanic acid Thiocyanic acid Cyanogen iodide Cyanogen bromide Cyanogen chloride Cyanogen fluoride Acetonitrile Aminoacetonitrile Glycolonitrile Cyanogen
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
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 pK_a 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.