General procedure for the synthesis of 2-methyl-5-fluorobenzoic acid from carbon dioxide: Commercially available 2-bromo-4-fluorotoluene (5 g) was dissolved in ether (appropriate amount). About 1/3 of this solution was taken and magnesium shavings (761 mg) were added and covered with ether (25 ml). Once the reaction was initiated, the remaining 2-bromo-4-fluorotoluene solution was added slowly and dropwise. The reaction mixture was kept at reflux for 2 hours. The resulting Grignard reagent was poured into a mixture of ether (750 ml) containing crushed dry ice. The reaction mixture was allowed to warm up gradually to room temperature. Subsequently, the solvent was removed by evaporation and the resulting residue was dissolved in ethyl acetate (100 ml) and extracted with 1N aqueous hydrochloric acid (100 ml). The organic phase was dried with magnesium sulfate, filtered and concentrated to give 2-methyl-5-fluorobenzoic acid (2.3 g; 56% yield).1H-NMR (CDCl3) δ: 2.5 (s, 3H), 7.0-7.2 (m, 2H), 7.7 (m, 1H).
