Formation of Haloarenes From Diazonium Salts

Benzene diazonium salt is formed by treating an aromatic primary amine with NaNO₂ and dil. HCl at low temperature. The process is known as diazotisation.

Diazonium salts are highly reactive compounds. They are used in the preparation of a large number of arene derivatives. When a diazonium salt is treated with copper (I) chloride (Cu₂Cl₂) or copper (I) bromide (Cu₂Br₂), the corresponding haloarene is formed. This reaction is known as Sandmeyer reaction. It is used for introducing a chloro or bromo group in the benzene ring.

Haloarenes can also be prepared by reacting benzene diazonium chloride with copper powder in presence of corresponding halogen acid. This reaction is called Gattermann reaction.