Potassium carbonate (16.6 g) and potassium cyanide (7.8 g) were added to a solution of 3-[4-fluoro-3-nitrophenyl]-6-trifluoromethyl-1,2,3,4-tetrahydropyrimidine-2,4-dione (31.9 g) in 250 ml of anhydrous N,N-dimethylformamide. The reaction mixture was subsequently stirred for a total of 45 hours at 75-80° C., with two further additions of potassium cyanide (in total 4.6 g) since the reaction had not proceeded completely. For working-up, water (250 ml) was added to the reaction mixture after it had cooled. The pH was subsequently brought to 2-3 by adding 60 ml of 1 N. hydrochloric acid. After nitrogen had been passed through the mixture for 4 hours to expel the hydrocyanic acid which had been liberated, the precipitate formed was separated off, washed with water and petroleum ether and dried. Yield: 17.0 g; m.p.: 135° C.
