Diazonium salts

Diazonium salts are prepared by diazotisation of primary aromatic amines and are used in preparation of aryl halides, aryl nitriles,and azo dyes

1. Module : Reaction Mechanism Topic : Diazonium Salts Author : Dr. M. T. Bachute Dept of Chemistry KBPM Pandharpur

2. DIAZONIUM SALTS Discovered by : John Peter Griess A German Chemist in 1858

3. Structure Ar-N2-x is called as aryl diazonium salt is called as diazonium ion. X = Cl - chloride, so 4 --

4. Diazotisation The process of conversion of aromatic primary amine into diazonium salt is called as diazotisation .

5. Sandmeyer and Gatterman Reactions Replacement of diazonium group Preparation of chlorobenzene and bromobenzene

6. Replacement of diazonium group Formation of iodobenzene and benzene H 3 PO 2 hypophosphorus acid H 3 PO 3 Phosphoric acid

7. Azo coupling Diazonium salts under suitable conditions react with reactive aromatic compounds phenols and amines to form coupled compound of the type Diazonium salt couples with phenols in alkaline medium. Diazonium salt couples with amines in acidic medium . e.g. Synthesis of methyl orange : Methyl orange is acid dye, used to dye silk and wool. But it is not fast to light and washing. In alkali it is yellow and in acid it is red. So it is used as an indicator. Sulphanilic acid is is coupled with N,N-dimethyl aniline under acidic conditions followed by treatment with alkali. Step I Preparation of Diazonium salt from sulphanilic acid.

8. Step II : Coupling diazonium salt couples with N,N-dimethyl aniline Step III : Reaction with alkali

9. Congo Red *It is an diazo dye, containing two azo groups. *It is a direct dye for cotton. *It is used as an indicator also( Blue in acidic solution and red in alkaline solution) Structure:

10. Synthesis of Congo Red Congo red is synthesised by coupling between tetrazotised benzidine and two molecules of naphthionic acid. Step I : preparation of tetrazotised benzidine

11. Step II : Coupling of tetrazotised benzidine with naphthionic acid