DIAZONIUM SALT:  

When primary aromatic amine is treated with nitrous acid in a cool solution, product is unstable compound, known as diazonium salt.  

      872_DIAZONIUM SALT.JPG  

This reaction is known as diazotisation. Diazonium salts have the structure  

      1409_diazotisation.JPG  

Mechanism of diazotisation:        

      197_Mechanism of diazotisation.JPG  

Illustration . Why ice cold condition have to be maintained in the diazotisation reaction of aniline?  

Solution. Because benzene diazonium chloride is unstable and decomposes to give phenol above 278 K.                                                

Exercise .       

      Explain:  

      (i) mineral acid is added in excess in diazotization of arylamines.  

      (ii) Aryl diazonium ions are more stable than alkyl diazonium ions. Explain    

Reactions of diazonium salts:  

These salts give substitution reactions and coupling reactions as follows:  

Substitution reactions:    

 2134_Substitution reactions.JPG

 
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