Formation of 1,1,3,3-tetrafluorophthalans in reactions of phthalic and pyromellitic acids with sulphur tetrafluoride

Abstract

Phthalic and pyromellitic acids were previously reported to react with SF 4 giving the respective bis- and tetrakis(trifluoromethyl)benzenes as sole products. We have found that the reaction with tetrafluorophthalic acid 1a and 4,5-bis(trifluoromethyl)phthalic acid 1b afford, beside the expected poly(trifluoromethyl)benzenes 2a and 2b, considerable amounts of 1,1,3,3- tetrafluorophthalans 3a and 3b. ▪ Similarly, from pyromellitic acids 4a and 4b mixtures of tetrakis(trifluoromethyl)benzenes 5a, 5b, phthalans 6a, 6b and benzodifurans 7a, 7b were obtained. ▪ Structural factors in the acids influencing the competitive formation of (trifluoromethyl)benzenes and cyclic phthalans will be discussed.