Abstract 4-Sulpho-2, 3, 5, 6-tetrafluorobenzoic acid (I) has been synthesised from pentafluorobenzoic acid via the oxidation of 4-mercapto-tetrafluorobenzoic acid. Reaction of I with DMF/SOCl 2 gave 1, 4-ClC 6 F 4 COCl (IIA) which was converted to 1, 4-ClC 6 F 4 COF (IIB) by fluoride exchange. Reaction with methanol or aniline gave respectively the methyl ester 1, 4-ClC 6 F 4 CO 2 Me (IIIA) and anilide 1, 4-ClC 6 F 4 CONHPh (IIIB). ...