Sodium tetrafluorocobaltate

The tetrafluorocobaltates of the alkali metals show12 considerable differences in their reactions with benzene. Lithium tetrafluorocobaltate(III) at 100-130 C gives 3,3,6,6-tetra-fluorocyclohexa-1,4-diene (13) of over 90% purity. This compound has long been postulated1,549 as a major intermediate in the fluorination with cobalt(III) fluoride. The sodium, potassium, and rubidium salts give similar product mixtures (ca. 8 compounds), most being polyfluoroenes (e.g. 14, 8% 15, 12% 16, 35%). 

Thiophene 1 was fluorinated with potassium tetrafluorocobaltate(III) (KC0F4) to give a mixture of hexafluorotetrahydrothiophene 15 and 2,2,5,5-tetrafluoro-2,5-dihydrothiophene 17 as major products. When hexafluorotetrahydrothiophene 15 was bubbled through molten potassium hydroxide, tetrafluorothiophene 19 was formed in low yield. When sodium methoxide was used, substitution of fluoride took place [15]. 2,5-Difluorothiophene 18 was obtained in 50 % yield by heating of 2,2,5,5-tetrafluoro-2,5-dihydrothiophene 17 with sodium fluoride at 530 °C. These conditions were found to be optimal, since the reaction did not occur at moderate temperatures (<480 °C). However, at 530 °C side reactions also took place, thus accounting for the only moderate yield of 2,5-difluorothiophene 18 [16]. 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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