14-3 Biological Chemistry. 



such as aniline in excess of an acid, cooling the solution 

 thus obtained, and then adding the theoretical amount of 

 amyl nitrite or sodium nitrite. In the former case alcohol 

 is used as a solvent to dilute the acid, and in the latter 

 case, water. The diazonium salt of the acid then separates 

 in a crystalline form. This is a general reaction when 

 the amino group is directly attached to a carbon atom of 

 the benzene ring. 



The diazonium salts undergo certain characteristic 

 reactions : 



(a) With alcohol the whole diazonium group is re- 

 placed by hydrogen, the alcohol being oxidized to 

 aldehyde 



C 6 H 6 -N 2 .C1 + C 2 H 6 OH = C 6 H 6 + N 2 + HC1 + CH 3 -CHO 



(b) On warming with water, the diazonium group is 

 replaced by a hydroxyl group to yield a phenol 



C 6 H 5 .N 2 .C1 + H 2 = C 6 H 5 OH + N 2 + HC1 



If nitrous acid is added to an aromatic amine without 

 cooling, the diazonium compound is not produced, but a 

 phenol is obtained directly. In this case the action is the 

 same as that of a primary aliphatic amine. 



(c) They undergo a characteristic reaction when 

 treated with cuprous salts, such as the chloride, bromide, 

 or cyanide, yielding chloro-, bromo-, or cyano-derivatives 

 respectively, the chlorine, bromine, or cyanogen replacing 

 the diazonium group. An addition product with the 

 cuprous salt is formed first, and this then decomposes 



C 8 H 5 .N 2 C12CuCl = 

 C a H 5 .N 2 Cl-2Cu(CN) = 



This reaction is known as Sandmeyer's reaction, and is 

 commonly employed for preparing halogen and cyanogen 

 compounds. It may be cited as an example of the method 



