SolutionsReactivity
1. Acid versus ketone
Acetone reacts with methylmagnesium bromide to give a tertiary alcohol. What happens if acetic acid is treated with the same reagent?
An acid-base reaction: the Grignard reagent removes the OH proton, giving methane and bromomagnesium acetate. The negatively charged carboxylate is no longer attacked by the nucleophile.
2. Acid or base catalysis?
Why are addition-elimination reactions on carboxylic acids carried out in acidic and not in basic medium?
In basic medium the acid is converted into the carboxylate, whose negative charge repels the nucleophile and which has no good leaving group. In acidic medium, protonation of the C=O increases the electrophilicity of the carbon and the OH leaves as water, a good leaving group.