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Example 10: Synthesis of 4,6-dimethoxy-2-(methylsulfonyl)pyrimidine To 200 mL of acetic acid was added 3% sodium tungstate as a catalyst. Subsequently, 1.0 mol of 2-methylsulfanyl-4,6-dimethoxypyrimidine was added to the solution and stirred until completely dissolved to form a clarified solution. The reaction mixture was heated to 40°C. Over a period of 4-8 hours, 2.1 mol of 30% H2O2 solution was slowly added to the heated reaction mixture and stirring was continued at 40 °C for 3-5 hours. After that, 0.05 mol of 30% H2O2 solution was added supplementally and stirring was continued at the same temperature until the reaction was complete (the progress of the reaction was monitored by TLC or HPLC). After completion of the reaction, the reaction mixture was cooled to room temperature and the precipitated solid was collected by filtration. The resulting solid was washed sequentially with aqueous acetic acid and deionized water to remove impurities. Finally, the washed solid was dried under appropriate conditions to obtain the target product in 83% yield. The filtrate portion was extracted with dichloroethane, and after separating the organic layer, the dichloroethane layer was concentrated to give a residue of about 42 g containing a small amount of product in about 1-1.5% yield.