Darzens halogenation

Not to be confused with Darzens reaction.

Darzens halogenation is the chemical synthesis of alkyl halides from alcohols via the treatment upon reflux of a large excess of thionyl chloride or bromide (SOX2) in the presence of small amounts of tertiary amine bases—such as pyridine or its corresponding hydrochloride. The reaction is named after its creator, Auguste George Darzens, who first reported it in 1911.[1][2] The procedure is effective for a wide range of alcohols including those that are difficult to halogenate, such as cyclohexanol (which normally decomposes to form cyclohexene if reacted with only SOCl2).[3] The reaction takes place through an SN2 mechanism but is also often used in the description of SNi mechanisms.

Example:

CH3CH2OH + SOX2 + pyridine → CH3CH2X + SO2 + HX where X = Cl or Br

References

  1. ↑ Darzens, George (1911). "Nouvelle methode d'etherification des alcools par les hydracides". Compt. Rend. 152: 1314–1317.
  2. ↑ Darzens, George (1911). "Action du Chlorure de Thionyle en Presence d'une Base Tertiare sur quelques Ether d'Acides Alcohols.". Compt. Rend. 152: 1601–1603.
  3. ↑ LIBERMANN, D. (27 December 1947). "Interaction of Thionyl Chloride and Hydroxy Compounds". Nature 160 (4078): 903–904. doi:10.1038/160903a0.