Polyfluoroarenes. Part XVIII. Some reactions of 2,3,4,5,6-pentafluorobiphenyl and related compounds

Abstract

2,3,4,5,6-Pentafluorobiphenyl reacts with boiling fuming nitric acid to give 2,4-dinitrobenzoic acid, but under mild conditions the 2′-, 3′-, and 4′-nitro-derivatives are formed in the ratio 3·4 : 1·0 : 8·7. All three nitro-compounds may be synthesised unambiguously by mixed Ullmann reactions. 2,3,4,5,6-Pentafluoro-3′-nitrobiphenyl is also isolated following the oxidation of pentafluorophenylhydrazine in nitrobenzene, and reacts with hot fuming nitric acid to give 3,4-dinitrobenzoic acid. Syntheses of 2,3,5,6-tetrafluoro-4-hydroxy-, -4-methoxy-, and -4-iodo-biphenyl are also described; irradiation of the iodo-compound in benzene gives 2′,3′,5′,6′-tetrafluoro-p-terphenyl, and its Ullmann condensation provides a good route to 2′,2″,3′,3″,5′,5″,6′,6″-octafluoro-p-quaterphenyl.