Darzens halogenation is the chemical synthesis of
alkyl halides from
alcohol
Alcohol most commonly refers to:
* Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom
* Alcohol (drug), an intoxicant found in alcoholic drinks
Alcohol may also refer to:
Chemicals
* Ethanol, one of sev ...
s via the treatment upon reflux of a large excess of
thionyl chloride or
thionyl bromide
Thionyl bromide is the chemical compound SOBr2. It is less stable and less widely used than its chloride analogue, thionyl chloride. It is prepared by the action of hydrogen bromide on thionyl chloride, a characteristic reaction where a stronger ac ...
(SOX
2) 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.
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 SOCl
2.
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
Chloroethane, commonly known as ethyl chloride, is a chemical compound with chemical formula CH3CH2Cl, once widely used in producing tetraethyllead, a gasoline additive. It is a colorless, flammable gas or refrigerated liquid with a faintly sweet ...
(X=Cl) or
bromoethane
Bromoethane, also known as ethyl bromide, is a chemical compound of the haloalkanes group. It is abbreviated by chemists as EtBr (which is also used as an abbreviation for ethidium bromide). This volatile compound has an ether-like odor.
Prepar ...
(X=Br) as follows:
::CH
3CH
2OH + SOX
2 CH
3CH
2X + SO
2 + HX
References
{{Organic reactions
Halogenation reactions
Substitution reactions
Name reactions