Preparation of 2,4-dioxo-1,2,3,4-tetrahydro-s-triazino-[1,2-a]-benzimidazoles

A process for the preparation of a 2,4-dioxo-1,2,3,4-tetrahydro-s-triazino-[1,2-a]-benzimidazole of the formula ##STR43## comprising reacting a benzimidazole compound of the formula ##STR44## or of the formula ##STR45## with a diphenyl carbonate of the formula ##STR46## in which R.sup.1 represents alkyl with 1-18 carbon atoms which can optionally be substituted in the .omega.-position by chlorine, CN, phenyl, alkoxycarbonyl with 1 to 4 carbon atoms in the alkoxy part, alkenoxycarbonyl with 1 to 3 carbon atoms in the alkenoxy part, -alkylaminocarbonyl, phenoxycarbonyl, morpholino, piperidino, pyrrolidino or dialkylamino with 1 to 4 carbon atoms per alkyl part, or represents phenyl which can optionally be substituted by chlorine, methyl or trifluoromethyl, or represents alkenyl with up to 18 carbon atoms, or represents dialkylamino with 1 to 4 carbon atoms per alkyl part, and R.sup.2 represents hydrogen, alkyl with 1-4 carbon atoms or trifluoromethyl,

• R.sup.3 may have any of the meanings of R.sup.1 or represents hydroxycarbonylalkyl with up to 18 methylene units, and
• R.sup.4 represents hydrogen, alkyl or halogen.