Darzens halogenation

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 a small amount a nitrogen base, such as a tertiary amine or pyridine, or the corresponding hydrochloride. The reaction is named after its creator, Auguste George Darzens, who first reported it in 1911. 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). The reaction takes place through an S_N2 mechanism but is also often used in the description of SNi mechanisms.

Example: