Benzyl chloroformate


Benzyl chloroformate is the benzyl ester of chloroformic acid. Also known as benzyl chlorocarbonate it is an oily colorless liquid although impure samples appear yellow. It is also known for its pungent odor. In contact with water it degrades.

Preparation

It is prepared in the lab by treating benzyl alcohol with phosgene. Phosgene is used in excess to minimise the production of the carbonate.

Amine protection

The “carboxybenzyl group” is commonly used in organic synthesis for the introduction of the carboxybenzyl protecting group for amines. It is a key protecting group for amines, suppressing its nucleophilic and basic properties.
Alternatively, as in the Curtius rearrangement, carboxybenzyl can be generated by the reaction of an isocyanate with benzyl alcohol.
Common amine protection procedures include:
The method was first used by Max Bergmann and Leonidas Zervas in 1932 for the synthesis of peptides. The abbreviation Z is in honor of Zervas.

Deprotection

in the presence of a variety of palladium-based catalysts is the usual method for deprotection. Palladium on charcoal is typical.
Alternatively, strong Lewis acids have been used, provided that a trap is provided for the released benzyl carbocation. The protected amine can be deprotected by catalytic hydrogenation or treatment with HBr, yielding a terminal carbamic acid that then readily decarboxylates to yield the free amine. Typically hydrogen gas and activated palladium on carbon are used.