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 secondary and/or tertiary amines and the acid(s) are selected from hydrofluoric, hydrochloric, hydrobromic and hydroiodic acid and 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, wherein the temperature of the reaction mixture at no time exceeds 39° C.
