cyanic acid [sī′an·ik ′as·əd]
Cyanic Acid
an equilibrium mixture of two tautomeric forms, cyanic acid (I) and isocyanic acid (II), the latter being more common under ordinary conditions:
Cyanic acid is a colorless, highly mobile liquid, with a sharp odor. It has a melting point of – 80°C, a boiling point of 23.6°C, and a density of 1.14 g/cm3 (at 0°C). It is readily soluble in water and ether. An aqueous solution of cyanic acid is a rather strong acid, with a dissociation constant of 1 × 10–4. Liquid cyanic acid polymerizes spontaneously even at 0°C, and at 20°C it sometimes explodes upon polymerization. The polymerization products are the cyclic trimer cyanuric acid, (HOCN)3, and the linear polymer cyamelide, (HOCN)n. Cyanic acid hydrolyzes readily in dilute aqueous solutions, a process that proceeds particularly rapidly in the presence of mineral acids:
HOCN + H2O →CO2 + NH3
Cyanic acid may be produced by the catalytic oxidation of hydrocyanic acid at temperatures of 560°C–640°C or by the thermal depolymerization of cyanuric acid in a stream of carbon dioxide. It is an intermediate in the industrial synthesis of melamine from urea. Among the derivatives of cyanic acid that have the greatest practical importance are cyanogen chloride, calcium cyanamide, and the cyanates.
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