Question 15.2: Devising a Synthesis Route for a Carboxylic Acid How would y...

Devising a Synthesis Route for a Carboxylic Acid

How would you prepare phenylacetic acid (PhCH_{2}CO_{2}H) from benzyl bromide (PhCH_{2}Br)?

Strategy
We’ve seen two methods for preparing carboxylic acids from alkyl halides:
(1) cyanide ion displacement followed by hydrolysis and (2) formation of a
Grignard reagent followed by carboxylation. The first method involves an S_{N}2 reaction and is therefore limited to use with primary and some secondary alkyl halides. The second method involves formation of a Grignard reagent and is therefore limited to use with organic halides that have no acidic hydrogens or reactive functional groups elsewhere in the molecule. In the present instance, either method would work well.