Perjluorop -x ylene, and TetraJtuoro-phthalic and -terephthalic Acid.Defluorination of perfluoro-l,2-and -1,4-dimethylcyclohexane by iron at 450-500" has given perfluoro-o-and -p-xylene respectively. With concentrated sulphuric acid these gave respectively tetrafluoro-phthalic and -terephthalic acid. The former was converted into its anhydride and imide and thence into tetrafluoroanthranilic acid. By decarboxylation each phthalic acid gave the expected tetrafluorobenzene. THIS paper describes the preparation of perfluoro-o-and -$-xylene by defluorination 2s3 of the corresponding perfluoro-alicyclic compounds, perfluoro-1,2-and -lJ4-dimethylcyclohexane.* These were prepared by the vapour-phase fluorination of o-and +-xylene respectively with cobalt trifluoride at 300-350" in a stirred reaction vesseL5 They were defluorinated by passage over iron gauze heated to about 450--500", giving perfluoro-oand -9-xylene, respectively. About 35% of the starting materials were recovered, yields being 40--45y0 based on that consumed. The yields and ease of formation of these compounds from the respective dimethylcyclohexanes are similar to those of perfluorotoluene from perfluoromethylcyclohexane,2 and show a considerable improvement over the case of perfluorocy~lohexane.~ Thus it appears that, although the introduction of a tertiary carbon atom into an alicyclic fluorocarbon, as in perfluoromethylcyclohexane, reduces the difficulty of defluorination of the compound, a second tertiary atom, as in the perfluorodimethylcyclohexanes, has little further effect.The trifluoromethyl groups of perfluoro-o-and -+-xylene were hydrolysed by fuming sulphuric acid at 150", to give respectively, in good yield, tetrafluorophthalic and tetrafluoroterephthalic acid. The o-acid gave di-S-benzylthiouronium and disilver salts, but only a monoanilinium salt, despite the use of an excess of aniline. Tetrafluoroterephthalic acid gave di-salts with the same three bases and also a dimethyl ester.Tetrafluorophthalic acid was converted into its anhydride by treatment with trifluoroacetic anhydride. Unlike phthalic anhydride, tetrafluorophthalic anhydride reacted readily with water. It dissolved almost instantaneously to give a solution that could be titrated with alkali just as though it were one of the free acid. The ease of hydrolysis Gething, Patrick, Stacey, and Tatlow, Nature, 1959, 183, 588. Coe, Patrick, and Tatlow, I'efnrhedvo,z, 1960, 9, 240.