Sandmeyer reaction

What is Sandmeyer reaction?

The Sandmeyer reaction, or Sandmeyer transformation, is a chemical process that involves the substitution of diazonium groups in aromatic compounds with either halo or cyano groups in the presence of cuprous salts.

Sandmeyer reaction
Sandmeyer reaction

Sandmeyer discovered this reaction in 1884 while attempting to produce phenylacetylene from benzenediazonium chloride and cuprous acetylide.

The reaction involves two steps for synthesizing aryl halides or cyanides from primary aryl amines: first, the formation of diazonium salts using nitrous acid, and then the transformation of diazo intermediates into aryl halides or cyanides using cuprous halides or cyanide.

The Sandmeyer nitrile synthesis refers to the specific preparation of aryl nitrile through this reaction, and the Sandmeyer reagent is the combination of alkali halide and cuprous halide.

Interestingly, the halo group introduced into the aromatic ring comes from cuprous halide, rather than the diazonium halide. Evidence for this includes the formation of p-dichlorobenzene from p-chlorobenzenediazonium bromide and cuprous chloride, as well as the production of p-chloro-bromobenzene from p-chlorobenzenediazonium chloride and cuprous bromide.

Halogen exchange has also been observed in the Sandmeyer reaction, though it is not promoted by cupric or ferrous chloride. A saturated solution of CaCl2, ZnCl2, and zinc ammonia chloride [Zn(NH3)2Cl2] with maximal concentration of chloride ions reacts well with aryl diazonium salt to yield aryl chloride.

Additionally, the yield of aryl nitrile can be improved by reacting the diazonium salt with nickel cyanide Ni(CN)2 rather than CuCN. Other cyanide salts, such as those with Fe, Cr, and Zn, are not effective.

Interestingly, iodonation of the aromatic diazonium salt does not require the presence of cuprous iodide. However, the reaction typically yields less than a quantitative yield of aryl halide due to the formation of side products such as biaryl, azobenzene, and phenol.


  • Sandmeyer, T. (1884), Ueber die Ersetzung der Amidgruppe durch Chlor in den aromatischen Substanzen. [On the replacement of the amide group by chlorine in aromatic substances.] Ber. Dtsch. Chem. Ges., 17: 1633-1635.
  • Sandmeyer, T. (1884), Ueber die Ersetzung der Amid-gruppe durch Chlor, Brom und Cyan in den aromatischen Substanzen. [On the replacement of the amide group by chlorine, bromine and cyanogen in aromatic substances.] Ber. Dtsch. Chem. Ges., 17: 2650-2653.