Isocyanic acid

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Structural formula
Structure of isocyanic acid
Surname Isocyanic acid
Molecular formula HNCO
Brief description

Liquid that is not very stable above 0 ° C and tends to polymerize

External identifiers / databases
CAS number 75-13-8
EC number 616-189-3
ECHA InfoCard 100.109.068
PubChem 6347
Wikidata Q25774
Molar mass 43.03 g · mol -1
Physical state


Melting point

- 86 ° C

boiling point

23.5 ° C

pK s value


safety instructions
GHS labeling of hazardous substances
05 - Corrosive 07 - Warning 08 - Dangerous to health


H and P phrases H: 302-312-314-332-334-335
P: ?
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

The isocyanic acid is a reactive, little resistant Cyansauerstoffsäure which is liberated from their salts by careful acidification and at temperatures above 0 ° C polymerized . It can be kept for weeks in benzene or ether below 0 ° C. As a solution in ice water, the more dilute the solution, the longer it can be kept. Their esters are called isocyanates ; their salts are usually not referred to as isocyanates but as cyanates . The free acid polymerizes very easily to form a mixture of cyanuric acid and cyamelide . Analogous to other pseudohalogens , it can also form a dimerdiisooxocyan ” OCN-NCO.

The cyanic acid than their tautomeric form is very unstable and is formed during the acidification of cyanates only in trace amounts (up to 3%).

Isocyanic acid is formally the imide of carbonic acid .

See also

Individual evidence

  1. a b Entry on isocyanic acid. In: Römpp Online . Georg Thieme Verlag, accessed on June 13, 2014.
  2. ^ A b c d A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 101st edition. Walter de Gruyter, Berlin 1995, ISBN 3-11-012641-9 .
  3. Template: CL Inventory / not harmonized There is not yet a harmonized classification for this substance . A labeling of isocyanic acid in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), which was retrieved on July 19, 2019, is reproduced from a self-classification by the distributor .
  4. Beyer-Walter, Textbook of Organic Chemistry, 23rd edition, S. Hirzel Verlag 1998.
  5. ^ Wissenschaft-Online-Lexika: Entry on Cyanate in the Lexikon der Chemie. , accessed February 24, 2009.