Benzyl

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Overview

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The structure of a benzyl cation

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 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.