- Appel reaction
The Appel reaction is an
organic reaction that converts analcohol into analkyl chloride usingtriphenylphosphine andcarbon tetrachloride . [cite journal
title = Tertiary Phosphane/Tetrachloromethane, a Versatile Reagent for Chlorination, Dehydration, and P-N Linkage
author = Rolf Appel
journal = Angewandte Chemie International Edition in English
volume = 14
issue = 12
pages = 801–811
year = 1975
url =
doi = 10.1002/anie.197508011]The Appel reaction is a mild method of halide introduction, and is successful on primary, secondary, and most tertiary alcohols. The use of
carbon tetrabromide orbromine as a halide source will yield alkyl bromides, while usingmethyl iodide oriodine will givealkyl iodide s.Reaction mechanism
The initial step of the Appel reaction is the formation of the
phosphonium salt pair 2.Deprotonation of the alcohol, formingchloroform 3, yields an alkoxide ion pair 4. Thenucleophilic displacement of the chloride by the alkoxide yields intermediate 5. With primary and secondary alcohols, the chloride anion reacts in a SN2 process forming the desired alkyl chloride 6 andtriphenylphosphine oxide 7. Tertiary alcohols form the products 6 and 7 via a SN1 mechanism.The driving force behind this and similar reactions is provided by the formation of solid triphenylphosphine oxide, which phase separates from the reaction mixture.
The yields are almost quantitative.
An example is the chlorination of
geraniol to geranyl chloride. [OrgSynth | author = Jose G. Calzada and John Hooz | title = Geranyl chloride| collvol = 6 | collvolpages = 634 | prep = cv6p0634] ,References
ee also
*
Mitsunobu reaction
*Organophosphorus chemistry
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