Process for the preparation of a compound of general formula (I): ##STR00001## in which X represents a halogen atom, by reaction of para-trifluoromethylaniline of formula (II): ##STR00002## with a dihalogen X.sub.2, the two compounds being introduced simultaneously into a polar aprotic solvent in a dihalogen/compound (II) molar ratio ranging from 1.9 to 2.5 and at a temperature ranging from 100 to 300.degree. C.