General procedure for the synthesis of dimethyl 5-fluoroisophthalate from methanol and 5-fluoroisophthalic acid: to a solution of 5-fluoroisophthalic acid (1.3 g, 7.1 mmol) in methanol (30 ml) was added concentrated sulfuric acid (0.25 ml). The reaction mixture was heated to reflux for 12 hours. After completion of the reaction, methanol was removed by distillation under reduced pressure. The residue was neutralized with saturated sodium bicarbonate solution and subsequently extracted with dichloromethane. The organic phase was washed with saturated sodium chloride solution, dried over anhydrous sodium sulfate, and concentrated under reduced pressure to give dimethyl 5-fluoroisophthalate 1.25 g (83% yield) as a white solid. Nuclear magnetic resonance hydrogen spectroscopy (NMR) data: δ 8.42 (s, 1H), 7.88 (d, 2H), 3.90 (s, 6H).
