Arenediazonium salt reaction with CuBr

For the in situ preparation of the required arenediazonium salt from an aryl amine by application of the diazotization reaction, an acid HX is used, that corresponds to the halo substituent X to be introduced onto the aromatic ring. Otherwise—e.g. when using HCl/CuBr—a mixture of aryl chloride and aryl bromide will be obtained. The copper-(l) salt 2 (chloride or bromide) is usually prepared by dissolving the appropriate sodium halide in an aqueous solution of copper-(ll) sulfate and then adding sodium hydrogensulfite to reduce copper-(ll) to copper-(1). Copper-(l) cyanide CuCN can be obtained by treatment of copper-(l) chloride with sodium cyanide. 

Cuprous bromide, CuBr Reacts with arenediazonium salts to yield bromoarenes (Sandmeyer reaction Section 24.8). 

Sandmeyer Reaction (Section 23.8E) Treatment of an arenediazonium salt with CuCl, CuBr, or CuCN results in replacement of the diazonium group by —Cl, — Br, or —CN, respectively. 

Sandmeyer reaction reaction of an arenediazonium salt with CuBr, CuCl, or CuCN (19.21). 

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