Gattermann Reaction

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

Concept: A modification of the Sandmeyer reaction where copper powder ($$\text{Cu}$$) in the presence of halogen acid ($$\text{HCl}$$ or $$\text{HBr}$$) is used instead of cuprous salts to introduce halogens onto the aromatic ring.