The reaction: ${\mathrm{ArN}}_2\mathrm{Cl}\stackrel{\mathrm{Cu}/\mathrm{HCl}}{\to }\mathrm{ArCl}+{\mathrm{N}}_2$ is known as :

$\begin{array}{l}{\mathrm{ArN}}_2^{+}{\mathrm{Cl}}^{-}\stackrel{\mathrm{Cu}/\mathrm{HCl}}{\to }\mathrm{ArCl}+{\mathrm{N}}_2\\ {\mathrm{ArN}}_2^{+}{\mathrm{Cl}}^{-}\stackrel{\mathrm{Cu}/\mathrm{HBr}}{\to }\mathrm{ArBr}+{\mathrm{N}}_2\\ {\mathrm{ArN}}_2^{+}{\mathrm{Cl}}^{-}\stackrel{\mathrm{Cu}/\mathrm{kCN}}{\to }\mathrm{ArCN}+{\mathrm{N}}_2\end{array}$

Copper powder and HX(or) KCN when heated with Benzene diazonium chloride gives  ${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{X}\left(\mathrm{or}\right){\mathrm{C}}_6{\mathrm{H}}_5\mathrm{CN}.$ This reaction is Gattermann’s reaction.

Note:– If ${\mathrm{Cu}}_2{\mathrm{Cl}}_2/\mathrm{HCl},{\mathrm{Cu}}_2{\mathrm{Br}}_2/\mathrm{HBr},{\mathrm{Cu}}_2{\left(\mathrm{CN}\right)}_2/\mathrm{KCN}$  are used the reaction is Sandmeyer reaction where the reactants and product being the same.