THE PRINCIPLES OF ORGANIC CHEMISTRY 57 



the replacement of the NH 2 group by the hydroxyl group 

 H, thus : 



R-NH 2 + HONO = K OH + N 2 + H 2 



When two atoms of hydrogen in ammonia are replaced 

 the group NH is left, which is known as the imino group. 

 This also is characterised by its reaction with nitrous acid 

 when substances known as oximes are obtained, thus : 



R 2 NH + HONO = R 2 N NO + H 2 



'Finally all three hydrogen atoms in ammonia may be 

 replaced and we obtain a tertiary amine, R 3 N. 



Compounds are known which are derived from a com- 

 bination of two amino groups joined thus : 



H 2 N NH 2 



This substance has been prepared and is known as hydra- 

 zine ; its phenyl derivative C 6 H 5 HN NH 2 has already been 

 mentioned more than once, and is a substance of great import- 

 ance because of its property of combining with the carbonyl 

 group which occurs in numerous sugars, and of thus giving 

 rise to crystallisable compounds. 



Cyanides. The group CN is an important one because of 

 the facility with which on treatment with water (in presence 

 of acid or alkali) it gives rise to the group COOH, that is, to 

 acids, thus : 



RON + 2H 2 = RCOOH + NH 3 



Such a process in which one or more molecules of water 

 take part is generally known as hydrolysis. 



Moreover, on treatment with nascent hydrogen, it is 

 reduced, forming an amino derivative, thus : 



X NH 2 



