Darzens halogenation

What is Darzens halogenation?

The Darzens halogenation method, also known as the synthesis of alkyl halides, was first reported by Darzens in 1911. It involves the conversion of alcohols to alkyl halides via treatment with thionyl chloride, SO2Cl, or bromide, SO2Br, in the presence of small amounts of tertiary amines such as pyridine. This general method provides good yields for the preparation of alkyl halides and eliminates the need for halogen derivatives of phosphorus, which can cause isomerization, polymerization, and the Walden Inversion of certain optically active alcohols.

However, it should be noted that when alcohols are treated with equivalent amounts of thionyl chloride in the presence of pyridine, no chlorination occurs and the resulting product is alkyl sulfite rather than alkyl halide. To produce alkyl halides, a large excess of thionyl halide and a small amount of pyridine is necessary, and refluxing is required.

Darzens halogenation - synthesis alkyl halides
Darzens halogenation


  • G. Darzens, Compt. Rend. 152, 1314 (1911)
  • G. Darzens, Compt. Rend. 152, 1601 (1911)
  • G. Darzens, Compt. Rend. 154, 1615 (1912)