The synthesis of tetrafluoro-sulphobenzoic acids and their derivatives

Abstract

The tetrafluorosulphobenzoic acids 1,2-HO2C.C6F4.SO3H (I) and 1,4-HO2C.C6F4.SO3H (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 SoCl2 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/SOCl2 gave 1,4-Cl.C6F4.COCl. The diacid fluorides 1,2-FOC.C6F4.SO2F (VI) and 1,4-FOC.C6F4.SO2F (VII) were obtained when (I) and (II) respectively were reacted with sulphur tetrafluoride. The use of excess SF4 gave 1,2- or 1,4- [F3C.C6F4.SO2F].