Methyl 4-acetamido-2-hydroxybenzoate (61.4 g, 294.0 mmol) was dissolved with stirring in dichloroethane (1.2 L) followed by the addition of N-chlorosuccinimide (58.8 g, 441 mmol). The reaction mixture was heated to reflux for 3 hours. Upon completion of the reaction, the volatile solvent was removed by distillation under reduced pressure. Water (1.0 liter) was added to the residue to precipitate the solid product, which was collected by filtration. The crude product was dissolved in a solvent mixture of methanol and dichloromethane (1:9 v/v) and washed with saturated brine. The organic layer was dried over anhydrous sodium sulfate and concentrated under reduced pressure to afford methyl 4-acetamido-5-chloro-2-hydroxybenzoate (67.7 g) in 94.6% yield. The structure of the product was confirmed by nuclear magnetic resonance hydrogen spectroscopy (DMSO-d6): δ 10.49 (broad single peak, 1H), 9.47 (single peak, 1H), 7.75 (single peak, 1H), 7.72 (single peak, 1H), 3.85 (single peak, 3H), 2.16 (single peak, 3H); mass spectrometry analysis showed the molecular ion peaks (m/z) to be 244 and 246 (M+H)+.
