Explain the following reactions
a) Sand meyer reaction
b) Gattermann’s reaction

a) Sandmeyer’s reaction:
The nucleophiles like Cl^–, Br^–, CN^–, are introduced in the benzene ring when bezene diazonium halide reacts with HCl, HBr & KCN in the presence of cuprous ion.

b) Gatterman Reaction: Cl^– and Br^– are introduced in the benzene ring when benzene diazonium chloride reacts with HCl (or) HBr in the presence of copper powder