Benzyl
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
In organic chemistry, benzyl is the term for the radical, ion or functional group C6H5CH2, which can be obtained formally by removing a hydrogen atom from toluene's methyl group. The benzyl functional group is sometimes abbreviated "Bn", not to be confused with "Bz", which is short for the benzoyl group. For example, benzyl alcohol can be abbreviated to BnOH.
In substituent nomenclature, benzyl and phenyl are commonly confused. Benzyl can be seen as a phenyl attached to a CH2 before attaching to the parent compound.
Benzyl protective groups
Benzyl groups are frequently used in organic synthesis as protective group for alcohols and carboxylic acids.
Two common methods for benzyl ether protection:
- reaction of alcohol with benzyl bromide and a strong base such as sodium hydride as in a Williamson ether synthesis
- reaction of alcohol with benzyl trichloroacetimidate (C6H5CH2OC(CCl3)=NH) promoted by trifluoromethanesulfonic acid
The benzyl group can be removed by hydrogenation.
One study [1] employs a benzyl pyridinium salt as a benzyl donor for alcohols.
The solvent is trifluoromethylbenzene and magnesium oxide is an acid scavenger. The reaction type for this conversion is believed to be SN1 based on the detection of trace amounts of Friedel-Crafts reaction sideproducts with toluene as a solvent.
References
- ↑ K. W. C. Poon and G. B. Dudley (2006). "Mix-and-Heat Benzylation of Alcohols Using a Bench-Stable Pyridinium Salt". J. Org. Chem. 71 (10): 3923–3927. doi:10.1021/jo0602773.