General procedure for the synthesis of 4-acetamido-3-methylbenzoic acid from 4-amino-3-methylbenzoic acid: triethylamine (121 g, 1.19 mol) was added to a dichloromethane (800 mL) suspension of 4-amino-3-methylbenzoic acid (60 g, 0.40 mol), and the reaction mixture became a clarified solution. Subsequently, acetic anhydride (81 g, 0.79 mol) was added and the reaction mixture was stirred at room temperature for 60 hours. After completion of the reaction, the solvent was removed by evaporation. The residue was diluted with water (400 mL) and extracted with ethyl acetate (3 x 600 mL). The organic extracts were combined, dried with magnesium sulfate, filtered and the solvent evaporated to give the title compound 4-acetamido-3-methylbenzoic acid as a brown solid (43 g, 56% yield). The product was characterized by 1H-NMR (d6-DMSO, 300 MHz): δ 9.36 (s, 1H), 7.77 (s, 1H), 7.10 (s, 2H), 2.27 (s, 3H), 2.10 (s, 3H). lC/MS analysis showed tR = 1.22 min, 194 (MH)+.
