Reactions of tetrafluorophthalic and difluoropyromellitic acids with sulphur tetrafluoride

Fluorination of tetrafluorophthalic acid ( 1 ) with an SF 4 /HF mixture at 190–300°C afforded,beside the expected perfluoro- o -xylene ( 2 ) and perfluoro- o -toluyl fluoride ( 4 ), considerableamounts of octafluoro-1,3-dihydroisobenzofuran ( 3 ). The reaction with difluoropyromelliticacid ( 5 ) at 190°C gave a mixture of perfluoro-2,4,5-trimethylbenzoyl fluoride ( 9 ),perfluoro-2,5-dimethylterephthaloyl difluoride ( 10a ), perfluoro-2,4-dimethylisophthaloyl difluoride( 10b ) and perfluoro-5-methyl-6-fluoroformyl-1,3-dihydroisobenzofuran ( 11 ), but at 300°C perfluorodurene ( 6 ), perfluoro-5,6-dimethyl-1,3-dihydroisobenzofuran ( 7 ) and perfluoro-2,4,5-trimethylbenzoyl fluoride ( 9 ) were obtained in a 3:1:0.8 ratio.