General procedure for the synthesis of 2-aminoterephthalic acid from 2-nitroterephthalic acid: in typical experiments, a mixture of nitroaromatic compounds (1.0 mmol), ammonium formate (3.3 mmol, 208 mg, 1.1 eq.), palladium catalyst (10% Pd/C, 2 mol%, 21 mg), and silicon dioxide (175 mg) was ball-milled in the presence of anhydrous methanol (η= 0.25 μL/mg) was ball-milled for 90 min in the presence of anhydrous methanol (η= 0.25 μL/mg). Upon completion of the milling, a small amount (~1 mg) of the crude reaction mixture was suspended in methanol and analyzed by thin-layer chromatography (TLC, usually using a solvent mixture of dichloromethane: methanol = 20:1 as eluent). The crude product was placed in a well-ventilated fume hood overnight, then suspended in methanol and filtered through a Büchner funnel. The filtrate is evaporated to give the target product 2-aminoterephthalic acid. If necessary, the final product can be further purified by column chromatography.
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