The Sandmeyer Reaction is a versatile route for synthesizing aryl halides from primary aromatic amines.

1. Diazotization: $Ar-N{H}_2+NaN{O}_2+2HCl\stackrel{0-5^{\circ }C}{\to }Ar-N_2^{+}C{l}^{-}+NaCl+2H_{2}O$
2. Sandmeyer Step: The benzene diazonium chloride is treated with a Copper(I) salt solution.

• $Ar-N_2^{+}C{l}^{-}\stackrel{CuCl/HCl}{\to }Ar-Cl+N_2$
• $Ar-N_2^{+}C{l}^{-}\stackrel{CuBr/HBr}{\to }Ar-Br+N_2$
• Note: $Ar-I$ is prepared simply by shaking with $KI$, without the need for a Copper(I) salt.