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:

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

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

8. Mechanism of diazotisation:

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

11. • 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

12. 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. This
reactions are known as sandmeyer
reaction.

13. • 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.

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

15. 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.

16. 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.

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

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