Methanol → 4,6-Dimethoxy-2-methylthiopyrimidine

A stirred solution of 162.8 grams (0.832 mole) of 4,6-dichloro-2-methylthiopyrimidine in 325 mL of methanol was cooled to 15° C., and 419 mL (1.83 mole) of sodium methoxide (25% in methanol) was added dropwise at a rate to maintain the reaction mixture temperature below 20° C. Upon completion of the addition, which required 45 minutes, the reaction mixture was allowed to warm to ambient temperature where it was stirred for 18 hours. After this time the reaction mixture was concentrated under reduced pressure to a residual solid. The solid was dissolved in 850 mL of ethyl acetate. The solution was washed with one 500 mL portion and two 200 mL portions of water, and then with one 200 mL portion of an aqueous solution saturated with sodium chloride. The aqueous washes were combined and extracted with one 350 mL portion of ethyl acetate. The ethyl acetate extract was then washed with one 150 mL portion of an aqueous solution saturated with sodium chloride. The ethyl acetate layers and extracts were combined and dried with magnesium sulfate. The mixture was filtered, and the filtrate was concentrated under reduced pressure to yield 155.0 grams of 4,6-dimethoxy-2-methylthiopyrimidine, which solidified upon standing; m.p. 50°-52° C. The reaction was repeated several times.