SolutionsFrom Organometallics
1. Pivalic acid
How would you prepare 2,2-dimethylpropanoic acid from 2-bromo-2-methylpropane? Would the cyanide route work?
With magnesium in dry ether, tert-butylmagnesium bromide is formed, which is treated with CO2 (dry ice) and then with H3O+.
The cyanide route does not work: a tertiary halide does not undergo SN2 and, with a basic nucleophile such as cyanide, gives mainly elimination (2-methylpropene).
2. Incompatible groups
Why can 4-hydroxybenzoic acid not be prepared by forming the Grignard reagent of 4-bromophenol directly?
The phenolic OH is acidic and destroys the Grignard reagent, a very strong base, as soon as it forms (phenol would be obtained). The OH must first be protected, for example as an ether, and deprotected at the end.