Methanol → 3-Amino-4-methylthiophene-2-carboxylic acid

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To a solution of methyl 3-amino-4-methyl-2-thiophene carboxylate (5 g, 29 mmol) and sodium hydroxide (3.5 g, 88 mmol) in a mixed solution (methanol:H2O/30 ml:120 ml) was heated at 50° C. for over night. The solution was cooled to room temperature and extracted with methylene chloride. The aqueous phase was acidified with 6N HCl until pH equal to 5. The aqueous phase was extracted again with ethyl acetate, and solvent phase washed with brine and dried over by sodium sulfate. After filtered and dried over the solvent, evaporated solvent to give 3.85 g of 3-amino-4-methyl-thiophene-2-carboxylic acid as a white solid in 84% yield: 1H NMR (300 MHz, CDCl3) δ 7.05 (d, 1H), 3.12 (br, 2H), 2.16 (s, 3H); MS (m/e): 157.9 (M+1).

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