Method for synthesizing anticoccidial drug toltrazuril for animals

The invention discloses a method for synthesizing an anticoccidial drug toltrazuril. The method comprises the following steps: mixing 3-methyl-4-(4-trifluoromethylthio-phenoxy)aniline with methylaminoformyl chloride, reacting in an organic solvent A at 30-100 DEG C for 1-6 h, carrying out post-treatment on a reaction solution A obtained after the reaction is completed, dissolving the obtained 1-methyl-3-[3-methyl-4-(4-trifluoromethylthio-phenoxy)phenyl]urea crude product into an organic solvent B, adding an inorganic acid at 0-40 DEG C, carrying out a reaction for 1-5 h, adding an aqueous cyanate solution, carrying out a thermal insulation reaction for 2-12 h at 35-50 DEG C to obtain a reaction solution B, and carrying out post-treatment to obtain 3-methyl-1-[3-methyl-4-(4-trifluoromethylthiophenoxy)phenyl]biuret; and mixing diethyl carbonate with an alkaline substance, adding the 3-methyl-1-[3-methyl-4-(4-trifluoromethylthiophenoxy)phenyl]biuret at 40-80 DEG C, carrying out a heat preservation reaction for 2