Chemistry: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 thionyl bromide (SOX2) in the presence of a small amount of a nitrogen base, such as a tertiary amine or pyridine or its corresponding hydrochloride or hydrobromide salt. The reaction is named after its creator, Auguste Georges Darzens, who first reported it in 1911.[1][2][3]
The addition of the amine and use of a large excess of the thionyl halide as compared to the usual halogenation protocol makes this reaction 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.[4] The reaction takes place through an SN2 mechanism but is also often used in the description of SNi mechanisms.
For example, ethanol can be converted into chloroethane (X=Cl) or bromoethane (X=Br) as follows:
- CH3CH2OH + SOX2 [math]\displaystyle{ \xrightarrow{pyridine} }[/math] CH3CH2X + SO2 + HX
References
- ↑ Darzens, George (1911). "Nouvelle methode d'etherification des alcools par les hydracides" (in French). Compt. Rend. 152: 1314–1317. http://gallica.bnf.fr/ark:/12148/bpt6k3105c/f1314.image.langFR.
- ↑ Darzens, George (1911). "Action du Chlorure de Thionyle en Presence d'une Base Tertiare sur quelques Ether d'Acides Alcohols." (in French). Compt. Rend. 152: 1601–1603. http://gallica.bnf.fr/ark:/12148/bpt6k3105c/f1601.image.langFR.
- ↑ "Darzens Halogenation". Comprehensive Organic Name Reactions and Reagents. 2010. pp. 846–847. doi:10.1002/9780470638859.conrr179. ISBN 9780471704508.
- ↑ Libermann, D. (27 December 1947). "Interaction of Thionyl Chloride and Hydroxy Compounds". Nature 160 (4078): 903–904. doi:10.1038/160903a0. PMID 18917309. Bibcode: 1947Natur.160..903L.
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