Methanol → Dimethyl 4-bromoisophthalate

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To a solution of 4-bromoisophthalic acid 201 (10 g, 40.8 mmol) in methanol (150 mL) was added concentrated sulfuric acid (3.5 mL). The solution mixture was heated at reflux temperature for 24 hours. After the reaction was complete, the methanol solvent was removed under reduced pressure. The residue was made basic with saturated sodium bicarbonate (NaHCO3). The solution was extracted with ethyl acetate. The extract was washed with water and dried over sodium sulfate (Na2SO4). Removal of solvent gave oil, which solidified at ambient temperature. The solid was titurated twice with 20 mL of methanol and hexane (1:3) to give 8 g (90%) of 4-bromoisophthalic acid dimethyl ester 202: 1H NMR (400 MHz, CDCl3) δ 3.93 (s, 3H), 3.93 (s, 3H), 7.74 (d, J=8 Hz, 1H), 7.95 (dd, J=2 Hz, J=8 Hz, 1H), 8.43 (d, J=2 Hz, 1H).

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