Sandmeyer Reaction

$$\text{Ar--N}_2^+\text{Cl}^- \xrightarrow{\text{Cu}_2\text{Cl}_2 / \text{HCl}} \text{Ar--Cl} + \text{N}_2 \uparrow$$

$$\text{Ar--N}_2^+\text{Cl}^- \xrightarrow{\text{Cu}_2\text{Br}_2 / \text{HBr}} \text{Ar--Br} + \text{N}_2 \uparrow$$

Concept: Freshly prepared benzene diazonium chloride solution is treated with cuprous chloride ($$\text{Cu}_2\text{Cl}_2$$) or cuprous bromide ($$\text{Cu}_2\text{Br}_2$$) dissolved in its corresponding halogen acid to yield chlorobenzene or bromobenzene.

• Gives better yield than the Gattermann reaction.