[CH3:1][C:2]1[CH:10]=[C:6]([C:7]([OH:9])=O)[C:5]([OH:11])=[CH:4][CH:3]=1.[C:12](=O)([O-])[O-].[K+].[K+].CC(C)=O.S([O:27][CH3:28])(OC)(=O)=O>O>[CH3:12][O:11][C:5]1[CH:4]=[CH:3][C:2]([CH3:1])=[CH:10][C:6]=1[C:7]([O:27][CH3:28])=[O:9]5.07 g (33.32×10-3 mol) of 5-methylsalicylic acid and 22.33 g (161.6×10-3 mol) of anhydrous potassium carbonate are introduced into a 250-cm3 two-necked flask. 175 cm3 of anhydrous acetone are added under an inert atmosphere. The reaction mixture is stirred, 7.25 cm3 (76.62×10-3 mol) of dimethyl sulfate are added with a syringe and the mixture is brought to reflux for 6 h. Hydrolysis of the dimethyl sulfate is performed by adding 5 cm3 of water. After filtration and evaporation of the solvent, the residue is taken up with dichloromethane, dried over MgSO4 and then evaporated to dryness. The crude product is purified by chromatography on a silica column (eluent: CH2Cl2) to give 5.47 g (30.36×10-3 mol) of the expected ester, equivalent to a 91% yield.
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