How to convert toluene to P-Methyl benzoic acid ?
How about this?
Step 1. Friedel-Crafts halogenation
React the toluene with bromine in the presence of aluminium bromide.
Step 2. Carboxylation of a Grignard reagent
Form a Grignard reagent by the reaction with magnesium in dry ether, then add carbon dioxide.