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