What is Isocyanic acid?
Isocyanic acid is the simplest stable chemical compound that contains carbon, hydrogen, nitrogen, and oxygen, It is obtained by thermal decomposition of cyanuric acid and reacts with carboxylic acid chlorides to form the corresponding isocyanates.
What is isocyanic acid used for?
Isocyanates are used in the manufacture of foams, fibers, paint coatings, elastomers, and insulation applications. Occupational exposures to isocyanates are generally related to the vapor pressures of the individual compounds.
Is isocyanic acid a strong acid?
Isocyanic acid has been known since Liebig and Wöhler, but it has not previously been measured in the atmosphere. The compound is moderately acidic (pKa = 3.7) and unstable in pure form as it readily polymerizes.
Properties For Isocyanic Acid A-B
In aqueous solution it is a weak acid, having a pKa of 3.7:
HNCO ⇌ H+ + NCO−
Isocyanic acid hydrolyses to carbon dioxide and ammonia:
HNCO + H2O → CO2 + NH3
Dilute solutions of isocyanic acid are stable in inert solvents, e.g. ether and chlorinated hydrocarbons.
At high concentrations, isocyanic acid oligomerizes to give the trimer cyanuric acid and cyamelide, a polymer. These species usually are easily separated from liquid- or gas-phase reaction products.
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, HNCO, is a Lewis acid whose free energy, enthalpy and entropy changes for its 1:1 association with a number of bases in carbon tetrachloride solution at 25 °C have been reported. The acceptor properties of HNCO are compared with other Lewis acid in the ECW model.
Low-temperature photolysis of solids containing HNCO creates the tautomer cyanic acid H−O−C≡N, also called hydrogen cyanate. Pure cyanic acid has not been isolated, and isocyanic acid is the predominant form in all solvents. Sometimes information presented for cyanic acid in reference books is actually for isocyanic acid.