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The chlorination of the 2,4,5-trifluorobenzoic acid is carried out in the melt, under pressure and/or in a solvent, for example chlorosulphonic acid or oleum, in the presence of halogen transfer agents, for example iodine. 2,4,5-Trifluoro-3-chlorobenzoic acid is obtained in this reaction. However, since the reaction mixture still contains unchanged starting material and some 2,4,5,-trifluoro-3,6-dichlorobenzoic acid, the crude mixture is treated, without intermediate isolation, with thionyl chloride. The desired 2,4,5-trifluoro-3-chlorobenzoyl chloride is then obtained by fractional distillation. However, it is more favorable to carry out the separation by distillation of the acid fluorides.