CYANIC ACID AND CYANATES. Cyanic acid, NC.OH, was discovered by F. W0hler in 1824 who employed its salt, ammonium cyanate, in his famous synthesis of urea (1828) which served to break down the distinction between compounds arising only from the intervention of vital forces and com pounds producible artificially in the laboratory. The acid was prepared by distilling its polymeride, cyanuric acid, in a current of carbon dioxide (F. Wailer and J. v. Liebig, 1827), the vapours distilling over being condensed in a freezing mixture. It is a very volatile liquid of strong acid reaction, and is only stable below o°C. It has a smell resembling that of acetic acid. At o°C. it is rapidly converted into a mixture of cyanuric acid, CaN303H3, and another polymeride cyamelide (CNOH).r, a white amorphous powder, insoluble in water. Cyanogen chloride, CNC1, which may be regarded as the chloride of cyanic acid, is prepared by the action of chlorine on hydrocyanic acid or on mercury cyanide. It is a very poisonous volatile liquid, which boils at 15.5°C. (See CHEMICAL WARFARE.) The salts of cyanic acid are known as the cyanates, the two most important being potassium cyanate (KOCN) and ammonium cyanate . Potassium cyanate may be prepared by heating potassium cyanide with an oxidizing agent, or by heating potassium ferrocyanide with manganese dioxide, potassium car bonate or potassium dichromate. It crystallizes in flat plates and is readily soluble in alcohol or cold water. It is a somewhat im portant reagent, and has been used by Emil Fischer in various syntheses in the uric acid group. (See PURINES.) J. Walker and J. K. Wood (1900) prepared pure ammonium cyanate by the union of gaseous ammonia and cyanic acid, special precautions being taken to keep the temperature below the point at which the salt is transformed into urea. It crystallizes in fine needles, which melt suddenly at about 8o°C., then resolidify, and melt again at about 128° to 130°C. (this temperature being the melting point of urea).
Esters of normal cyanic acid are not known, but those of isocyanic acid (HN•CO) may be prepared by the action of alkyl halides on silver cyanate, or by oxidizing the isonitriles with mercuric oxide. They are volatile liquids which boil without de composition, and possess a nauseating smell. When hydrolysed with caustic alkalis, they yield primary amines (this reaction de termines their constitution) : = Ethyl isocyanate, a colourless liquid (b.p. 6o°C.) was first prepared by A. Wurtz (1854) by distilling a mixture of potassium ethyl sulphate and potassium cyanate.
Cyanuric acid, was obtained by Wohler and Liebig by heating urea, and by A. Wurtz by passing chlorine into melt ing urea. It forms white efflorescent crystals. Treatment with phosphorus pentachloride gives cyanuric chloride, which is also formed by the combination of anhydrous chlorine and prussic acid in the presence of sunlight. These substances contain a ring of three carbon and three nitrogen atoms.