Synthesis and reactions of 4-sulpho-2,3,5,6,-tetrafluorobenzoic acid

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 ). Treatment of I with PCl 5 gave the diacid chloride 1,4-ClOCC 6 F 4 SO 2 Cl ( IVA ) which was converted to IIB by the action of KF in tetraglyme. Stoichiometric reaction of I with SF 4 gave 1,4-FOCC 6 F 4 SO 2 F ( IVB ) while the use of excess reagent produced 1,4-F 3 CC 6 F 4 SO 2 F ( V ). Partial hydrolysis of IVB gave 1,4-HO 2 CC 6 F 4 SO 2 F ( VIA ) which was decarboxylated in DMSO to give 1,4- HC 6 F 4 SO 2 F ( VII ). The diacid halides IVA and IVB were readily derivatised with methanol or aniline to give respectively 1,4-MeO 2 CC 6 F 4 SO 2 Cl ( VIIIA ), 1,4-MeO 2 CC 6 F 4 SO 2 F ( VIB ), 1,4-PhNHOCC 6 F 4 SO 2 Cl ( VIIIB ) and 1,4-PhNHOCC 6 F 4 SO 2 F ( VIC ). Treatment of IVB with ethylene glycol gave 1,4-[CH 2 O 2 CC 6 F 4 SO 2 F] 2 ( IX ). Reaction of the methyl esters VIB and VIIIA with equimolar amounts of aniline afforded respectively (3-PhNH)-1,4- MeO 2 CC 6 F 3 SO 2 F ( X ) and 1,4-MeO 2 CC 6 F 3 SO 2 NHPh ( XI ). Analogous reaction of aniline with C 6 F 5 SO 2 F gave 1,4-PhHNC 6 F 4 SO 2 F.