AROMATIC COMPOUNDS 249 



Diazobenzene. C 6 H 5 . N : N . OH or C 6 H 5 . N( j N) . OH. 



Aniline is a primary amine. Primary amines of the aliphatic 

 series are converted by the action of nitrous acid into the correspond- 

 ing alcohol, but diazobenzene is formed by the action of nitrous acid 

 upon aniline : 



|NH fl 



The reaction is carried out at about o. 



Properties. 



Diazobenzene behaves like a strong base (NH 4 OH) and is known 

 only in the form of its salts. When liberated from a solution of its 

 salts it is precipitated as a yellow oil which is very unstable and 

 decomposes with explosion. It forms crystalline salts with mineral 

 acids, which are also explosive. The nitrate explodes violently if 

 gently struck ; the other salts explode on heating. These salts are 

 easily soluble in water, less soluble in alcohol and insoluble in ether. 

 They are generally called diazonium salts. 



Reactions. 



(1) An aqueous solution of a diazonium salt is decomposed on 

 boiling. Nitrogen is evolved and phenol is formed : 



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



Thus : 



A few drops of sodium nitrite solution are added to a dilute 

 solution of aniline in hydrochloric acid. Diazobenzene chloride is 

 formed. On warming the solution, it is decomposed with evolution 

 of nftrogen and the smell of phenol (carbolic acid) becomes noticeable. 



(2) On boiling a diazobenzene salt with absolute alcohol, nitrogen 

 is evolved and benzene is formed, reduction occurring : 



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



(3) A precipitate of diazobenzene perbromide is formed on adding 

 bromine dissolved in potassium bromide to a solution of diazoben- 

 zene chloride ; on boiling with alcohol, nitrogen is evolved and 

 bromobenzene is formed : 



C 6 H 5 N 2 C1 + Br 2 + KBr = KC1 + C 6 H 5 NBr . NBr 

 C 6 H 5 NBr . NBr 2 = C 6 H 5 Br + N 2 + Br 2 . 



(4) lodobenzene is formed if potassium iodide be added to a 

 solution of diazobenzene chloride and the solution warmed : 



C 6 H 5 N a Cl + KI = KCl + N 2 + C 8 H 5 I. 



