Water → 4-Methylbenzene-1,3-dicarboxylic acid

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5-Cyano-2-methyl-benzoic acid methyl ester (1.09 g, 6.22 mmol) was suspended in a mixture of water (25 mL) and concentrated sulfuric acid (10 mL). The yellow solution was stirred at 150° C. for 4 hours to give a pale yellow slurry. The reaction mixture was cooled to room temperature and the precipitate was isolated via suction filtration, washed with water (2×10 mL) and dried in vacuo to yield 4-methyl-isophthalic acid as a tan solid. The diacid was then suspended in MeOH (25 mL) and concentrated sulfuric acid (10 mL) and the resulting mixture was stirred at 90° C. for 14 hours to give a bright yellow solution. The MeOH was removed under reduced pressure and the remaining aqueous solution was diluted with brine (60 mL) and EtOAc (50 mL) and then neutralized with 3M NaOH until pH of aqueous layer was approximately 10. The mixture was extracted with EtOAc (3×100 mL), dried (Na2SO4), filtered, and concentrated in vacuo to give pure 4-methyl-isophthalic acid dimethyl ester as a pale orange solid (1.06 g, 82%, 2-steps). 1H NMR (CDCl3) δ 2.66 (s, 3H), 3.92 (s, 3H), 3.93 (s, 3H), 7.33 (d, 1H, J=9.0 Hz), 8.05 (dd, 1H, J=9.0, 3.0 Hz), 8.57 (d, 1H, J=3.0 Hz).

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