CYANAMIDE

cyanamide, nc.nh2, the amide of normal cyanic acid, obtained by the action of ammonia on cyanogen chloride, bromide or iodide, or by the desulphurization of thio-urea with mercuric oxide; it is generally prepared by the latter process. it forms white crystals, which melt at 40 deg. c., and are readily soluble in water, alcohol and ether. heated above its melting point it polymerizes to di-cyandiamide (cn2h2)2, which at 150 deg. c. is transformed into the polymer _n_-tri-cyantriamide or melamine (cn2h2)3, the mass solidifying. nascent hydrogen reduces cyanamide to ammonia and methylamine. it gives mono-metallic salts of the type nc.nhm when treated with aqueous or alcoholic solutions of alkalis. di-metallic salts are obtained by heating cyanates alone, e.g. calcium, or cyanides in a current of nitrogen, e.g. barium. calcium cyanamide has assumed importance in agriculture since the discovery of its economic production in the electric furnace, wherein calcium carbide takes up nitrogen from the atmosphere to form the cyanamide with the simultaneous liberation of carbon. it may also be produced by heating lime or chalk with charcoal to 2000 deg. in a current of air. the commercial product (which is known in germany as "_kalkstickstoff_") contains from 14 to 22% of nitrogen, which is liberated as ammonia when the substance is treated with water; to this decomposition it owes its agricultural value. it appears that with soils which are not rich in humus or not deficient in lime, calcium cyanamide is almost as good, nitrogen for nitrogen, as ammonium sulphate or sodium nitrate; but it is of doubtful value with peaty soils or soils containing little lime, nor is it usefully available as a top-dressing or for storing. cyanic acid and cyanates. cyanic acid, cn.oh, was discovered by f. wohler in 1824, and may be obtained by distilling its polymeride, cyanuric acid, in a current of carbon dioxide (f. wohler and j. v. liebig, _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 stable below 0 deg. c. it has a smell resembling that of acetic acid. at 0 deg. c. it is rapidly converted into a mixture of cyanuric acid, c3n3o3h3, and another polymer, cyamelide (cnoh)x; this latter substance is a white amorphous powder, insoluble in water. an aqueous solution of cyanic acid is rapidly hydrolysed (above 0 deg. c.) into a mixture of carbon dioxide and ammonia. cyanogen chloride, cncl, may be regarded as the chloride of cyanic acid. it may be 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 deg. c. it polymerizes readily to cyanuric chloride, c3n3cl3. 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 potassium cyanate (kocn) and ammonium cyanate (nh4ocn). potassium cyanate may be prepared by heating potassium cyanide with an oxidizing agent, or by heating potassium ferrocyanide with manganese dioxide, potassium carbonate or potassium dichromate (j. v. liebig, _ann._, 1841, 38, p. 108; c. lea, _jahresb._, 1861, p. 789; l. gattermann, _ber._, 1890, 23, p. 1224), the fused mass being extracted with boiling alcohol. it crystallizes in flat plates and is readily soluble in cold water. it is a somewhat important reagent, and has been used by emil fischer in various syntheses in the uric acid group (see purin). ammonium cyanate possesses considerable theoretical importance since the first synthetical production of an organic from inorganic compounds was accomplished by warming its aqueous solution for some time, urea being formed (f. wohler, _berzelius jahresberichte_, 1828, 12, p. 266). j. walker and j. k. wood (_jour. chem. soc._, 1900, 77, p. 24) 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 80 deg. c., then resolidify, and melt again at about 128 deg. to 130 deg. 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.) 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 decomposition, and possess a nauseating smell. when hydrolysed with caustic alkalis, they yield primary amines (this reaction determines their constitution). c2h5nco + h2o = c2h5nh2 + co2. when heated with water they yield carbon dioxide and symmetrical dialkyl ureas; with ammonia and amines they form alkyl ureas; and with acid anhydrides they yield tertiary amides. ethyl isocyanate, c2h5nco, was first prepared by a. 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 60 deg. c. _cyanuric acid_, h3c3n3o3, 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 phosphorus pentachloride gives cyanuric chloride, c3n3cl3, 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, i.e. they are symmetrical triazines.