The synthesis of tetrafluoro-sulphobenzoic acids and their derivatives

Abstract The tetrafluorosulphobenzoic acids 1,2-HO 2 C.C 6 F 4 .SO 3 H (I) and 1,4-HO 2 C.C 6 F 4 .SO 3 H (II) have been synthesised [1] by oxidation of respectively 4,5,6,7-tetrafluorobenzo [ b ] thiophen- 2-carboxylic acid (III) [2] and 4-mercaptotetrafluorobenzoic acid (IV) [3]. By-products were obtained when (III) was oxidised with either trifluoroperacetic acid or potassium permanganate. A number of reactions of these intermediates have been investigated and the products characterized, eg reaction of (I) with SoCl 2 gave tetrafluoro-1,2-sulphobenzoic acid cyclic anhyride (V). Although no significant change was observed when (II) was similarly treated reaction of (II) with DMF/SOCl 2 gave 1,4-Cl.C 6 F 4 .COCl. The diacid fluorides 1,2-FOC.C 6 F 4 .SO 2 F (VI) and 1,4-FOC.C 6 F 4 .SO 2 F (VII) were obtained when (I) and (II) respectively were reacted with sulphur tetrafluoride. The use of excess SF 4 gave 1,2- or 1,4- [F 3 C.C 6 F 4 .SO 2 F].