1 64 PRACTICAL ORGANIC AND BIO-CHEMISTRY 

 GUANIDINE AND ITS DERIVATIVES. 



Guanidine was first obtained by the oxidation of guanine (p. 294), and is 

 also a product of the oxidation of arginine (p. 165) with permanganate. Its 

 formation by the oxidation of arginine explains its formation in the oxidation 

 of proteins, which contain arginine. Guanidine has been found in self-digested 

 solutions of pancreas and in extracts of vetch seedlings and in the sap of the 

 beet. 



Guanidine is formed by the action of ammonia upon ortho-carbonic ester 

 in a manner similar to the preparation of urea from ethyl carbonate or car- 

 bonic ester (p. 129) : 



OC 2 H 5 /KH 2 /Nil 



H 5 //'NH 2 "1 ^ c=NH 



* C C \ 



H 3 \>NH[HJ NH 2 



OC 2 H 5 Vn 2 



Ortho-carbonic Hypothetical. Guanidine. 



ester. 



It is generally prepared by the action of ammonia upon cyanamide : 



NH 2 



H 2 N . C=N + NH 3 = C^NH 



NH 2 . 



In practice, this reaction is most conveniently accomplished by heating 

 ammonium thiocyanate to 180-190. Thiourea and cyanamide are formed. 

 The cyanamide reacts with ammonium thiocyanate to yield guanidine thio- 

 cyanate : 



NH 2 

 NH 4 SCN + NH 2 CN = C=NH 



Guanidine is thus urea in which the O atom has been replaced by the 

 =NH (imino) group. 



Guanidine is a deliquescent crystalline substance, easily soluble in water and 

 alcohol. It is a strong base ; its solutions have an alkaline reaction and absorb 

 carbon dioxide from the air forming guanidine carbonate, (CH 5 N 3 ) 2 . H 2 CO 3 , 

 which is soluble in water, but not in alcohol. Guanidine also forms salts 

 with other acids ; the nitrate, CH 5 N 3 . HNO 3 , is not easily soluble and consists 

 of large plates which melt at 214. The chief salt is the picrate which melts 

 at 315 and is very insoluble in cold water. This salt is used for the isolation 

 of guanidine from solution and for its estimation. Double salts are formed 

 with gold chloride and cadmium chloride. 



Guanidine is hydrolysed by alkalies into urea and ammonia : 

 NH 2 NH 2 



/ / 



C=NH + H O = C NH 2 + NH 3 . 



\NH. X 



