The reaction \(\mathrm{Ar}_2 \stackrel{\ominus}{\mathrm{C}} \stackrel{\oplus}{\mathrm{Cl}}+\mathrm{Cu}+\mathrm{HCl} \longrightarrow \mathrm{ArCl}+\mathrm{N}_2+\mathrm{CuCl}\) is known as

The reaction, \(\mathrm{Ar}_{\mathrm{N}}^2 \mathrm{Cl}^{-}+\mathrm{Cu}+\mathrm{HCl} \longrightarrow \mathrm{ArCl}+\mathrm{N}_2+\mathrm{CuCl}\) is known as Gattermann reaction where diazonium salt reacts with copper metal in present of \(\mathrm{HCl}\) to give chlorobenzene. This reaction uses \(\mathrm{ArSN}_1\) mechanism where diazonium group is a good leaving group that departs leading to phenyl carbocation formation which is very unstable and then the \(\mathrm{Nu}^{\circ}, \mathrm{Cl}^{-}\)attacks the phenyl carbocation giving chlorobenzene.