160 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Cyanamide is used in the synthesis of creatine and arginine (p. 165). 

 These compounds behave like cyanamide in giving urea on hydrolysis. 



Cyanic Acid. HOCN. 



Cyanic acid is formed by distilling cyanuric acid. 



A small quantity of cyanuric acid is placed in a small bulb blown upon 

 the end of a glass tube and the glass tubing is bent at an angle. The end of 

 the glass tube leads into a test tube surrounded by a freezing mixture. On 

 .heating, the cyanuric acid is decomposed and cyanic acid collects in the test 

 tube as a liquid. 



Cyanic acid is only stable below o and is a mobile, volatile liquid with 

 a strong acid reaction and with a smell resembling that of glacial acetic acid. 

 It produces blisters upon the skin. 



Pure cyanic acid, on exposure to the air, polymerises to cyanuric acid, 

 with explosiveness ; a small quantity, such as prepared above, polymerizes with 

 a cracking noise. 



It is an extremely unstable substance ; its aqueous solution above o de- 

 composes giving carbon dioxide and ammonia : 



HOCN + H 2 O = CO 2 + NH 3 . 



It dissolves in alcohol forming the ethyl ester of allophanic acid : 

 H 2 N.CO.NH. COOC 2 H 5 . 



Its salts are more stable than the free acid. 



Potassium Cyanate, KOCN. 



Potassium cyanate is formed by the oxidation of potassium cyanide 

 by a variety of oxidising agents, air, lead oxide, potassium perman- 

 ganate, or sodium hypochlorite. 



It may be prepared from potassium cyanide as follows : 



About I gm. of potassium cyanide is heated in a crucible in a fume 

 cupboard until it melts. Lead oxide is adcled in small quantities to 

 the fused mass so long as visible reduction occurs. The mass, when 

 cold, is extracted with water ; potassium cyanate crystallises out on 

 evaporation. 



It may also be conveniently prepared from potassium ferrocyanide : a 

 mixture of 4 parts of potassium ferrocyanide and 3 parts of potassium 

 bichromate are carefully heated in an iron dish, avoiding the formation of 

 ammonia. The potassium cyanate is extracted with water. 



Potassium cyanate forms shining leaflets or quadratic plates. It 

 dissolves readily in cold water, with difficulty in hot alcohol. 



In aqueous solution it is unstable and decomposes forming ammonia 

 and potassium carbonate. 



This decomposition can be seen with the solution prepared above ; 

 carbon dioxide is evolved on adding sulphuric acid, and the presence 

 of ammonia may be shov/n by making alkaline, warming and testing 

 with red litmus. 



