The general procedure for the synthesis of 3,4-difluoro-2-hydroxybenzoic acid from 2,3,4-trifluorobenzoic acid was carried out as follows: solid sodium hydroxide (4.52 g, 113 mmol) was added batchwise to a solution of dimethylimidazolidinone (10 mL) of 2,3,4-trifluorobenzoic acid (5.0 g, 28 mmol) under the conditions of cooling in an ice bath and stirring. Subsequently, the reaction mixture was heated to 120 °C and maintained at this temperature for 2 h. During this time, the progress of the reaction was monitored by TLC to confirm the complete consumption of 2,3,4-trifluorobenzoic acid. Upon completion of the reaction, the mixture was cooled to room temperature and acidified to pH 5-6 with 2N hydrochloric acid (7.5 mL).The precipitated white solid was collected by filtration, washed with excess water, and dried to afford the target product, 3,4-difluoro-2-hydroxybenzoic acid (3.6 g, 73.4% yield), with a melting point of 174-177 °C. The product structure was determined by 1H-NMR. The structure of the product was confirmed by 1H-NMR (400 MHz, DMSO-d6) and IR (KBr) spectroscopy: 1H-NMR δ 6.94-7.01 (m, 1H, aryl), 7.64-7.68 (m, 1H, aryl); IR 3208.9 cm-1 (OH), 1654.1 cm-1 (C=O), 1625.7 cm-1 (C =C, aromatic), 1315.2 cm-1 (C-O).
