The Sandmeyer reaction is an organic reaction used to convert an aryl diazonium salt to an aryl halide using a copper(I) halide catalyst. The mechanism begins with a single electron transfer (SET) from the copper to the diazonium to form a neutral diaso radical and copper(II) halide. 146683-25-2 Chemscene The diazo radical then releases a molecule of nitrogen gas to form an aryl radical. 5-Fluoro-2-iodobenzoic acid methyl ester Formula The aryl radical reacts with the copper(II) halide to regenerate the copper(I) halide catalyst and yield the final aryl halide product. ^[1][2]