The present invention relates to a process for the sulfinylation of a pyrazole derivative, characterized in that 5-amino-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-1H-pyrazole-3-carbonitrile (II) is reacted with a sulfinylating agent S in the presence of at least one amine acid complex wherein the amine(s) are selected from cyclic secondary amines and the acid(s) are selected from sulfonic acid derivatives, and with the addition of a halogenating agent, wherein S is [CF3S(O)]2O； or CF3S(O)X wherein X means fluoro, chloro, bromo, iodo, a hydroxy group, or an alkaline or alkaline earth metal salt of the hydroxy group； or mixtures thereof.
