Patent ID: 8669371

Claim:
A process for the selective chlorination of a 4,5-dihydro-1-phenyl-1H-1,2,4-triazole-5-one in the 4-position of the phenyl ring; where the 4,5-dihydro-1-phenyl-1H-1,2,4-triazole-5-one is selected from the group consisting of 4,5-dihydro-3-methyl-1-phenyl-1H-1,2,4-triazole-5-one and 4-difluoromethyl-4,5-dihydro-3-methyl-1-phenyl-1H-1,2,4-triazole-5-one; which comprises the steps of: a) charging a reaction vessel with a polar aprotic solvent mixture and a 4,5-dihydro-1-phenyl-1H-1,2,4-triazole-5-one; b) cooling the 4,5-dihydro-1-phenyl-1H-1,2,4-triazole-5-one and solvent mixture to 0° C.; c) adding 1.5 equivalents of chlorine gas to the mixture over a period of 30 minutes while allowing the temperature to warm to 15° C.