Sandmeyer Reaction

a method of introducing a halogen atom into an aromatic ring by decomposition of a diazonium salt in the presence of a cuprous halide. The reaction is generally carried out by heating the reactants together in excess of halogen acid:

Aryl fluorides are prepared by a somewhat modified method (the Shiemann reaction):

Unlike other methods of introducing halogen into the aromatic ring (such as direct halogenation), the Sandmeyer reaction makes possible the production of aryl halides with the halogen atom in a strictly defined position. The Sandmeyer reaction is widely used to synthesize various aryl halides, many of which are important intermediates in dye production. The Sandmeyer reaction can be used to replace the diazo group by —CN, —SCN, —NO₂, —SH, and —N₃, as well as —AsO₃H₂ (the Bart reaction).

The Sandmeyer reaction was discovered by the Swiss chemist T. Sandmeyer in 1884.