Isocyanic acid

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Isocyanic acid
Isocyansäure.svg
Isocyanic acid 3D balls.png
Names
IUPAC name
Isocyanic acid
Identifiers
75-13-8 YesY
420-05-3 (cyanic acid) N
ChEBI CHEBI:29202 YesY
ChemSpider 6107 YesY
Jmol 3D model Interactive image
PubChem 6347
  • InChI=1S/CHNO/c2-1-3/h2H YesY
    Key: OWIKHYCFFJSOEH-UHFFFAOYSA-N YesY
  • InChI=1/CHNO/c2-1-3/h2H
    Key: OWIKHYCFFJSOEH-UHFFFAOYAE
  • O=C=[N@H]
Properties
HNCO
Molar mass 43.03 g/mol
Appearance Colorless liquid or gas (b.p. near room temperature)
Density 1.14 g/cm3 (20 °C)
Melting point −86 °C (−123 °F; 187 K)[1]
Boiling point 23.5 °C (74.3 °F; 296.6 K)
Dissolves
Solubility Soluble in benzene, toluene, ether
Vapor pressure {{{value}}}
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox references

Isocyanic acid is an organic compound with the formula HNCO, discovered in 1830 by Liebig and Wöhler.[2] This colourless substance is volatile and poisonous, with a boiling point of 23.5 °C. Isocyanic acid is the simplest stable chemical compound that contains carbon, hydrogen, nitrogen, and oxygen, the four most commonly found elements in organic chemistry and biology.

Preparation and reactions

Isocyanic acid can be made by protonation of the cyanate anion, such as from salts like potassium cyanate, by either gaseous hydrogen chloride or acids such as oxalic acid.[3]

H+ + NCO- → HNCO

HNCO also can be made by the high-temperature thermal decomposition of cyanuric acid, a trimer.

C3H3N3O3 → 3 HNCO

Isocyanic acid hydrolyses to carbon dioxide and ammonia:

HNCO + H2O → CO2 + NH3

At sufficiently high concentrations, isocyanic acid oligomerizes to give cyanuric acid and cyamelide, a polymer. These species usually are easily separated from liquid- or gas-phase reaction products. Dilute solutions of isocyanic acid are stable in inert solvents, e.g. ether and chlorinated hydrocarbons.[4]

Isocyanic acid reacts with amines to give ureas (carbamides):

HNCO + RNH2 → RNHC(O)NH2.

This reaction is called carbamylation.

HNCO adds across electron-rich double bonds, such as vinylethers, to give the corresponding isocyanates.

Isocyanic acid is also present in various forms of smoke, including smog and cigarette smoke. It was detected using mass spectrometry, and easily dissolves in water, posing a health risk to the lungs.[5]

Isomers: Cyanic acid and fulminic acid

Low-temperature photolysis of solids containing HNCO has been shown to make H-O-C≡N, known as cyanic acid or hydrogen cyanate; it is a tautomer of isocyanic acid.[6] Pure cyanic acid has not been isolated, and isocyanic acid is the predominant form in all solvents.[4] Note that sometimes information presented for cyanic acid in reference books is actually for isocyanic acid.

Cyanic and isocyanic acids are isomers of fulminic acid (H-C=N-O), an unstable compound.[7]

See also

References

  1. Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
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  4. 4.0 4.1 A. S. Narula, K. Ramachandran “Isocyanic Acid” in Encyclopedia of Reagents for Organic Synthesis, 2001, John Wiley & Sons, New York. doi:10.1002/047084289X.ri072m Article Online Posting Date: April 15, 2001.
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Further reading

  • Handbook of Chemistry and Physics, 65th. Edition, CRC Press (1984)

External links

  • Lua error in package.lua at line 80: module 'strict' not found.
  • Cyanic acid from NIST Chemistry WebBook (accessed 2006-09-09)