[Cl:1][C:2]1[CH:7]=[C:6]([OH:8])[N:5]=[C:4]([S:9][CH3:10])[N:3]=1.O.O1CCOCC1.Cl[CH:19]([F:21])[F:20]>[OH-].[K+].C1OCCOCCOCCOCCOCCOC1>[Cl:1][C:2]1[CH:7]=[C:6]([O:8][CH:19]([F:21])[F:20])[N:5]=[C:4]([S:9][CH3:10])[N:3]=16.8 g (0.036 mole) of 4-chloro-6-hydroxy-2-methylthiopyrimidine are suspended in 25 ml 50% potassium hydroxide solution, 25 ml of water and 100 ml of dioxane. After the addition of 0.5 g of 18-crown-6, the reaction mixture is heated to 40° C., and 10 g of chlorodifluoromethane are subsequently introduced over 3 hours. The mixture is then cooled to room temperature, the phases are separated and the organic phase is evaporated to dryness. The residue is crystallised from methanol/water, affording 6.9 g (84.4% of theory) of 4-chloro-6-difluoromethoxy-2-methylthiopyrimidine with a melting point of 36°-37° C. The substance has a boiling point of 76°-78° C. at 0.15 mbar.
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