[CH3:1][S:2][C:3]1[CH:11]=[CH:10][C:6]([C:7]([OH:9])=[O:8])=[C:5]([OH:12])[CH:4]=1.[C:13](OC(=O)C)(=[O:15])[CH3:14]>S(=O)(=O)(O)O.O>[CH3:1][S:2][C:3]1[CH:11]=[CH:10][C:6]([C:7]([OH:9])=[O:8])=[C:5]([O:12][C:13](=[O:15])[CH3:14])[CH:4]=1To a mixture of 4-methylthio-2-hydroxybenzoic acid (50.0 g, 272 mmol) and acetic anhydride (77.0 mL, 815 mmol) was added 36 N sulfuric acid (0.45 mL, 8.16 mmol) and the mixture was heated to 75° C. for 1 h. To the reaction mixture was added H2O (200 mL), and it was stirred for 18 h. A white precipitate was collected, triturated with dichloromethane, (100 mL), diluted with 20% Et2O/hexanes (300 mL), and filtered to give the title compound as a white solid (49 g, 80%).
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