NEW MATERIAL: A compound of formulae I and II (R1 and R2 are each a 1-6C alkyl, allyl, a 3-6C cycloalkyl, phenyl, etc.; R3 is phenyl, biphenyl or phenoxyphenyl) and its tautomer and salt.

EXAMPLE: 1,3-Dimethyl-5-[3,4-dichlorophenylcarbamoyl]-4(6)-oxo-6(4)-oxido-(1H,5 H)-pyrimidinium betaine.

USE: Anthelmintics.

PROCESS: Desulfurization of a compound of formula III gives a compound of formula I or II. The desulfurization is effected, for example, by hydrogenation with a hydrogenating agent (e.g. trialkyltin hydride, etc.). preferably by catalytic hydrogenation. The hydrogenation is carried out, for example, in an inert solvent or a mixed solvent at 20 to 180°C, preferably at 60 to 120°C.