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CYANIC ACID AND CYANATES

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Originally appearing in Volume V07, Page 680 of the 1911 Encyclopedia Britannica.
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CYANIC See also:

ACID AND CYANATES . Cyanic acid, CN•OH, was discovered by F. See also:Wohler in 1824, and may be obtained by distilling its polymeride, cyanuric acid, in a current of See also:carbon dioxide (F. Wohler and J. v. See also:Liebig, See also:Berzelius Jahresberichte, 1827, 11, p. 84), the vapours which distil over being condensed in a freezing mixture. It is a very volatile liquid of strong acid reaction, and is only See also:stable below o° C. It has a See also:smell resembling that of acetic acid. At o° C. it is rapidly converted into a mixture of cyanuric acid, C3N3O3H3, and another polymer, cyamelide (CNOH)x; this latter substance is a See also:white amorphous See also:powder, insoluble in See also:water. An aqueous See also:solution of cyanic acid is rapidly hydrolysed (above (a° C.) into a mixture of carbon dioxide and See also:ammonia. See also:Cyanogen chloride, CNC1, may be regarded as the chloride of cyanic acid. It may be prepared by the See also:action of See also:chlorine on hydrocyanic acid or on See also:mercury See also:cyanide.

It is a very poisonous volatile liquid, which boils at 15.5° C. It polymerizes readily to cyanuric chloride, C3N3C13. See also:

Caustic alkalis hydrolyse it readily to the alkaline chloride and cyanate. The salts of cyanic acid are known as the cyanates, the two most important being See also:potassium cyanate (KOCN) and ammonium cyanate (NH4OCN). Potassium cyanate may be prepared by See also:heating potassium cyanide with an oxidizing See also:agent, or by heating potassium ferrocyanide with See also:manganese dioxide, potassium carbonate or potassium dichromate (J. v. Liebig, See also:Ann., 1841, 38, p. 108; C. See also:Lea, Jahresb., 1861, p. 789; L. Gattermann, Ber., 1890, 23, p. 1224), the fused See also:mass being extracted with boiling See also:alcohol. It crystallizes in See also:flat plates and is readily soluble in See also:cold water.

It is a somewhat important reagent, and has been used by Emil See also:

Fischer in various syntheses in the uric acid See also:group (see See also:PuRIN). Ammonium cyanate possesses considerable theoretical importance since the first synthetical See also:production of an organic from inorganic compounds was accomplished by warming its aqueous solution for some See also:time, See also:urea being formed (F. Wohler, Berzelius Jahresberichte, 1828, 12, p. 266). J. See also:Walker and J. K. See also:Wood (Jour. Chem. See also:Soc., 1900, 77, p. 24) prepared pure ammonium cyanate by the See also:union of gaseous ammonia and cyanic acid, See also:special precautions being taken to keep the temperature below the point at which the See also:salt is trans-formed into urea. It crystallizes in See also:fine needles, which melt suddenly at about 8o° C., then resolidify, and melt again at about 128° to 130° C.

(this temperature being that of the melting point of urea). Substituted ammonias were also made to combine with cyanic acid, and it was found that the substituted ammonium cyanates produced pass much more readily into the corresponding ureas than ammonium cyanate itself. (On the constitution of cyanic acid see F. D. Chattaway and J. M. Wadmore, Jour. Chem. Soc., 1902, 81, p. 191.) See also:

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 See also:silver cyanate, or by oxidizing the isonitriles with mercuric See also:oxide. They are volatile liquids which See also:boil without decomposition, and possess a nauseating smell. When hydrolysed with caustic alkalis, they yield See also:primary See also:amines (this reaction determines their constitution).

C2H5NCO + See also:

H2O= C2H5NH2 + See also:CO2. When heated with water they yield carbon dioxide and symmetrical dialkyl ureas; with ammonia and amines they See also:form alkyl ureas; and with acid anhydrides they yield See also:tertiary amides. See also:Ethyl isocyanate, C2H5NCO, was first prepared by A. See also:Wurtz ( Ann.chim., 1854 (3), 42, p. 43) by distilling a mixture of potassium ethyl sulphate.and potassium cyanate. It is a colourless liquid which boils at 6o C. Cyanuric acid, H3C3N303, was obtained by Wohler and Liebig by heating urea, and by A. Wurtz by passing chlorine into melting urea. It forms white efflorescent crystals. Treatment with See also:phosphorus pentachloride gives cyanuric chloride, C3N3C13, which is also formed by the See also:combination of anhydrous chlorine and prussic acid in the presence of sunlight. These substances contain a See also:ring of three carbon and three See also:nitrogen atoms, i.e. they are symmetrical triazines.

End of Article: CYANIC ACID AND CYANATES

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