4-Amino-3-hydroxybenzoic acid

Step 1: Preparation of 3-hydroxy-4-nitrobenzoic acid (Compound 4A)

3-Hydroxybenzoic acid (220 mg, 1.6 mmol) was dissolved in acetonitrile, and after complete dissolution, ceric ammonium nitrate (1.26 g, 2.3 mmol) was added slowly in batches and stirred at room temperature overnight. The reaction was quenched with water at the end of the reaction, extracted with ethyl acetate, the organic terms were combined, dried, concentrated under reduced pressure and then chromatographed on a column (eluting with ethyl acetate) to obtain the solid product Compound 4A (85 mg, 27% yield).

Step 2, the preparation of 4-amino-3-hydroxybenzoic acid (compound 4B)

Compound 4A (85 mg, 0.8 mmol) was dissolved in methanol, Pd/C catalyst was added and then reacted at room temperature under the protection of hydrogen overnight, at the end of the reaction, the insoluble solid was filtered to remove the solid, and the organic layer was concentrated under reduced pressure to obtain the solid was not purified and used directly for the next step of the reaction.