Synthetic utility of aryl diazoniumsalts

it deals with reaction of diazonium salt to give different product and coupling reaction

1. Diazonium salts – Preparation, synthetic applications and uses.

2. Preparation of Diazonium salt:

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

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

5. Mechanism of diazotisation :

6. Reactions of diazonium salts: These salts give substitution reactions and coupling reactions as follows:

7. Reduction to arenes -A diazonium salt is reduced by hypophosphorous acid H3PO2 to give respective arene . Syntheis of phenol- aqueous solution of diazonium salt is acidified and heated to form phenol. This method is useful to prepare substituted phenol not obtained by electrophillic aromatic substitution of phenol.eg 2 bromo 4 methyl phenol and meta hydroxy acetophenone

8. Sandmeyer reaction When a cold solution of diazonium salt is treated with cuprous chloride, cuprous bromide or cuprous cyanide, the product is aryl chloride, aryl bromide and aryl cyanide. T his reactions are known as sandmeyer reaction.

9. Aryl nitriles hydrolysed to give carboxylic acid. This provides the useful method of introducing COOH group in the benzene ring where other methods are not applicable. The reduction of nitrile with sodium/ethanol or LiAlH4 gives the corresponding amine.

10. Synthesis of aryl iodides When an aqueous solution of diazonium salt is heated with excess of potassium iodide, aryl iodide is obtained.

11. Synthesis of aryl fluoride The diazonium salt is treated with fluroboric acid HBF4 when diazonium fluroborate precipitates.this is isolated dried and heated to give aryl fluorides.this is the procedure for preparing flurobenzene is called schiemann reaction.

12. Aryl reaction It is the convenient method for preparing unsymmetrical biaryls in which the diazonium group is replaced by an aromatic ring. Diazotisation is carried out in the usual way. The solution is madebasic , and the resulting solution is treated with arene at 0-5C.This reaction is called as Gomberg -Bachmann reaction. Yield is generally low but starting materials are often readily available.

13. COUPLING REACTIONS:   Coupling reactions are electrophilic substitution reactions. Some examples are as follows:

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