Sandmaeyer's Reaction - benzene diazonium salt

Replacement reaction of benzene diazonium chloride by halide ion

When the solution of freshly prepared benzene diazonium salt is trated with a mixture of cuprous chloride or cuprous bromide in presence of concentrated HCL or HBr, we get chlorobenzene or bromobenzene. This reaction is known as Sandmaeyer's reaction.

Alternatively the same reaction can be done by copper powder and cone. HX instead of cuprous halide and this modified reaction is called Gatterman reaction.

Indobenzene can be prepared from benzene diazonium salt by reacting with KI solution.
Replacement with fluoride is known as Balz Schiemann reaction.In this benzene diazonium salt is reacted with fluoroboric acid heated to get fluorobenzene.
Preparation of aryl halides from diazonium salt by replacement gives pure aryl halides and provides important synthetic route for preparation of aryl iodides and aryl fluorides.


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Reactions of benzene diazonium chloride

 Chemical reactions of benzene diazonium chloride

Due to unstable nature diazonium group ( -N₂^- X⁺ ) is a good leaving group. In most of the reactions of diazonium salt, -N₂^-X⁺  group is replaced by other groups. Such reactions are usually grouped under replacement reactions.

In the second type, due to electron deficiency (+ve charge) on diazonium ion, it can behave like an electrophile and couple with electron rich aromatic compounds and undergo coupling reactions.

Replacement reactions of benzene diazonium chloride

Depending on replacing groups these reactions can be mentioned under following heads. In this way we can easily introduce_F, -CI, -I, -OH and -CN groups in the aromatic ring.

1. Replacement by halide ion (Sandmaeyer's reaction)

2. Replacement by cyanide ion

3. Replacement with OH^- ion

4. Replacement with hydrogen

Diazonium salt

Diazonium salt reactions

Diazonium salts have N2 X functional group attached to an aryl group. They are highly unstable and are mainly used as a synthetic intermediate for various compounds. Alkyl diazonium salt do not exist even below 00C.
 
Nomenclature of Diazonium salt
 
The name is obtained by adding diazonium chloride, sulphate etc. to the name of parent hydrocarbon.

Methods of Preparation

Aromatic diazonium salts are prepared from aromatic primary amines. aromatic primary amine is taken in the ice-cold solution of HCL and adding sodium nitrite at 00C we get aromatic diazonium salt. This reaction is known as diazotisation.

Diazonium salt are highly unstable and they are not stored and they are not stored and are used immediately after their preparation.