Sandmeyer reaction
A benzene diazonium salt is converted to chlorobenzene, bromobenzene or benzonitrile by cuprous chloride, cuprous bromide or cuprous cyanide.
Benzene diazonium chlorideC₆H₅N₂⁺Cl⁻Diazonium salt - Step 1
Cu₂Cl₂, HCl
ChlorobenzeneC₆H₅ClHaloarene
How it works
- The primary aromatic amine is first diazotised with NaNO₂ and HCl at 273 to 278 K.
- The cuprous salt transfers its halide or cyanide to the aryl group.
- Nitrogen leaves as N₂ gas and the substituted benzene forms.
What it makes
Chlorobenzene, bromobenzene and benzonitrile from aniline.
Where it fails
The halogen must match the acid used (HCl with Cu2Cl2, HBr with Cu2Br2). Fluoro and iodo compounds are not made this way.
Class 12, Chapter 9 Amines
Sandmeyer reaction: quick answers
What is the difference between the Sandmeyer and Gattermann reactions?
Sandmeyer uses a cuprous salt (Cu2Cl2, Cu2Br2, CuCN) and gives better yields. Gattermann uses copper powder with the halogen acid.
Can the Sandmeyer reaction make iodobenzene?
No copper is needed for iodine. The diazonium salt is simply treated with KI.
Why must diazotisation be done at 273 to 278 K?
Above this range the diazonium salt decomposes, giving phenol and nitrogen.