New process for the preparation of 1,2,4-triazole-3-ones

The invention relates to a novel process for preparing 1,2,4-triazol-3-ones of the formula: (CF DRAWING IN BOPI) ** wherein R 1 represents a radical aliphatic, cycloaliphatic, phenyl, naphthyl or heterocyclic and R ** 2 represents an aliphatic, cycloaliphatic, phenyl, naphthyl or heterocyclic group which comprises reacting a monoacylhydrazine with phosgene to obtain a 1,3,4-oxadiazolin-2-one on which comprises reacting a primary amine to obtain a acylsemicarbazide and cyclizing the latter by alkaline treatment. 1,2,4-triazol-3-ones are useful as intermediates in the manufacture of medicaments , herbicides and polymers.