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.
- 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.
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.
Read more about this topic: Isocyanic Acid
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