Hydrogen cyanide

Hydrogen cyanide
Names
	IUPAC name Formonitrile
	Systematic IUPAC name Methanenitrile
	Other names Formic anammonide; Hydridonitridocarbon; Hydrocyanic acid (aqueous); Prussic acid; Cyanane;
Identifiers
CAS Number	74-90-8 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:18407 ;
ChemSpider	748 ;
ECHA InfoCard	100.000.747
EC Number	200-821-6;
KEGG	C01326 ;
MeSH	Hydrogen+Cyanide
PubChem CID	768;
RTECS number	MW6825000;
UNII	2WTB3V159F ;
UN number	1051
CompTox Dashboard (EPA)	DTXSID9024148 ;
	InChI InChI=1S/CHN/c1-2/h1H Key: LELOWRISYMNNSU-UHFFFAOYSA-N ;
	SMILES C#N;
Properties
Chemical formula	HCN
Molar mass	27.0253 g/mol
Appearance	Colorless liquid or gas
Odor	bitter 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)
Solubility in water	Miscible
Solubility in ethanol	Miscible
Vapor pressure	100 kPa (25 °C)
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)
Structure
Crystal structure	tetragonal (>170 K); orthorhombic (<170 K)
Point group	C∞v
Molecular shape	Linear
Dipole moment	2.98 D
Thermochemistry
Heat capacity (C)	35.9 J K−1 mol−1 (gas)
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:
Pictograms
Signal word	Danger
Hazard statements	H225, H300+H310+H330, H319, H336, H370, H410
Precautionary statements	P210, P261, P305+P351+P338
NFPA 704 (fire diamond)	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)
	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	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). verify (what is ?) Infobox references

Hydrogen cyanide (formerly known as prussic acid) is a chemical compound with the formula HCN and structural formula H−C≡N. It is a highly toxic 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.^[10] It is more toxic than solid cyanide compounds due to its volatile nature. A solution of hydrogen cyanide in water, represented as HCN(aq), is called hydrocyanic acid. The salts of the cyanide anion are known as cyanides.

Whether hydrogen cyanide is an organic compound or not is a topic of debate among chemists. It is traditionally considered inorganic, but can also be considered a nitrile,^[11] giving rise to its alternative names of methanenitrile and formonitrile.^[2]

^ "hydrogen cyanide (CHEBI:18407)". Chemical Entities of Biological Interest. UK: European Bioinformatics Institute. 18 October 2009. Main. Retrieved 2012-06-04.
^ ^a ^b ^c "Hydrogen Cyanide". PubChem. National Center for Biotechnology Information.
^ Simeonova, Fina Petrova; Fishbein, Lawrence (2004). Hydrogen cyanide and cyanides : human health aspects (Report). World Health Organization. ISBN 9241530618. ISSN 1020-6167.
^ ^a ^b ^c ^d ^e ^f Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. ISBN 978-1439855119.
^ Evans DA. "pKa's of Inorganic and Oxo-Acids" (PDF). Archived (PDF) from the original on 2022-10-09. Retrieved June 19, 2020.
^ Patnaik P (2002). Handbook of Inorganic Chemicals. McGraw-Hill. ISBN 978-0070494398.
^ Schulz, Axel; Surkau, Jonas (2022-09-21). "Main group cyanides: from hydrogen cyanide to cyanido-complexes". Reviews in Inorganic Chemistry. 43 (1). Walter de Gruyter GmbH: 49–188. doi:10.1515/revic-2021-0044. ISSN 0193-4929.
^ ^a ^b ^c ^d NIOSH Pocket Guide to Chemical Hazards. "#0333". National Institute for Occupational Safety and Health (NIOSH).
^ ^a ^b "Hydrogen cyanide". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
^ Gail, E.; Gos, S.; Kulzer, R.; Lorösch, J.; Rubo, A.; Sauer, M. "Cyano Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a08_159.pub2. ISBN 978-3-527-30673-2.
^ "Human Metabolome Database: Showing metabocard for Hydrogen cyanide (HMDB0060292)".

[1] "hydrogen cyanide (CHEBI:18407)". Chemical Entities of Biological Interest. UK: European Bioinformatics Institute. 18 October 2009. Main. Retrieved 2012-06-04.

[pubchem-2] "Hydrogen Cyanide". PubChem. National Center for Biotechnology Information.

[3] Simeonova, Fina Petrova; Fishbein, Lawrence (2004). Hydrogen cyanide and cyanides : human health aspects (Report). World Health Organization. ISBN 9241530618. ISSN 1020-6167.

[Haynes-4] ^ ^a ^b ^c ^d ^e ^f Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. ISBN 978-1439855119.

[5] Evans DA. "pKa's of Inorganic and Oxo-Acids" (PDF). Archived (PDF) from the original on 2022-10-09. Retrieved June 19, 2020.

[6] Patnaik P (2002). Handbook of Inorganic Chemicals. McGraw-Hill. ISBN 978-0070494398.

[7] Schulz, Axel; Surkau, Jonas (2022-09-21). "Main group cyanides: from hydrogen cyanide to cyanido-complexes". Reviews in Inorganic Chemistry. 43 (1). Walter de Gruyter GmbH: 49–188. doi:10.1515/revic-2021-0044. ISSN 0193-4929.

[PGCH-8] NIOSH Pocket Guide to Chemical Hazards. "#0333". National Institute for Occupational Safety and Health (NIOSH).

[IDLH-9] "Hydrogen cyanide". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).

[Ullmann-10] Gail, E.; Gos, S.; Kulzer, R.; Lorösch, J.; Rubo, A.; Sauer, M. "Cyano Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a08_159.pub2. ISBN 978-3-527-30673-2.

[11] "Human Metabolome Database: Showing metabocard for Hydrogen cyanide (HMDB0060292)".

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