Cesium tetrafluorocobaltate

At 320 °C, cesium tetrafluorocobaltate converts benzotrifluoride to /n-fluo-robenzotrifluoride, 2f/-heptafluorotoluene, octafluorotoluene, pertluoro-l -meth-ylcyclohexene, and perfluoromethylcyclohexane [29] l,3-Bis(trifluoromethyl)-benzene is convened at 420 °C to 4,5,6-trifluoro-l,3-bis(trifluoroethyl)bcnzene, perfluoro-l,3-dimethylbenzene, and perfluoro-l,3-dimethylcyclohexane [29], p-Xylene gives at 350 °C l,4-bis(difluoromethyl)tetrafluorobenzene, 1-di-fluoromethyl-3-trifluoromethyltetrafluorobenzene, perfluoro-1,3-dimethyl-benzene, and perfluoro-1,3-dimethyloyclohexane... 

Similarly complex is the fluorination of the Ihtes methylpyridines (a-, ()-, and 7-picolmes) with cesium tetrafluorocobaltate. 2-Methylpyridme was fluorinated at 270 °C for 180-200 mm, 3- and 4-methylpyridmes were fluorinated at 330 to 340 °C for 150 min All of them afforded the respective polyjluorinated pyridines and perfiuoro-1,2-, 1,3-dimethyl-, and 1-ethylpyrrolidine In addition, perfluoro-2-aza-2-hexene and bis(tnfluoromethyl)amine were isolated m variable yields [27] All the isolated products of the fluorination of 3-methylpyridme (3-picoline) are shown in equation 9. 

In quinoline and isoquinoline, the benzene ring is more receptive to fluorma-tion, its double bonds being saturated and the hydrogen atoms replaced in preference to those in the pyridine ring As with pyridine and its homologues, ring contraction takes place during fluorination with cesium tetrafluorocobaltate at... 

Fluorination. Direct fluorination of quinoline was accompanied by extensive fragmentation of the heteroring, but trifluoromethyl hypofluorite in trichlorofluoromethane at -70°C converted 5-fluoro-8-hydroxyquino-line into the 5,7-difluoro-8-hydroxy product (72JMC987). Quinoline, itself, was perfluorinated by fluorine and cobalt(III) fluoride (56JCS783), whereas cesium tetrafluorocobaltate at around 350°C converted it into a mixture of saturated polyfluoro compounds (82JFC413). It is much more satisfactory to introduce fluorine by nucleophilic methods. 

Cesium tetrafluorocobaltate(III) behaves quite differently 12,14 at 250CC it reacts with benzene to give some diene 13 (26%) and several aromatics [fluorobenzene (32%), pentafluorobenzene (9%), perfluorobenzene (4%), and others in lesser amounts]. 

When toluene is fluorinated65 over potassium tetrafluorocobaltate(III), the major products at 330-340cC are notable for being unsaturated and for containing a difluoromethyl group they are also similar in type to those produced in the potassium tetrafluorocobaltate(III)/ben-zene reaction. Over cesium tetrafluorocobaltate(III), toluene and -xylene give66 about 25-30 % of aromatic compounds. 

Pyridine and the methylpyridines are fluorinated over cobalt(III) fluoride, potassium tetra-fluorocobaltate(III) and cesium tetrafluorocobaltate(III). Only in the cesium tetrafluorocobalt-ate(III) reactions are significant quantities of polyfluoropyridines and -methylpyridines isolated. 

Cesium tetrafluorocobaltate(III) and pyridine at 300-400 C react to give96 significant quantities of polyfluoropyridines [25% altogether, with perfluoropyridine (15%) being the... 

The methylpyridines over cesium tetrafluorocobaltate(III) at 270-340°C also react to give97 significant quantities (10-37% of the product mixtures) of polyfluoropyridines (4-7 compounds, most of which have the ring fully fluorinated with the methyl groups converted into difluoromethyl or trifluoromethyl groups) and perfluoro(alkylpyrrolidines) (23-58%) in overall yields of about 30-35%. 

Cesium tetrafluorocobaltate(III) and quinoline react at 335-350°C to give98 over 60% of a mixture of 11 identified compounds two products 13 and 14 dominate the rest (each was about one-third of the product mixture). The rearranged structure of 14 is quite remarkable at first sight, but its formation resembles that of the polyfluoropyrrolidines from pyridines. Aromatic compounds are not so prominent as products as with other fluorinations over cesium tetrafluorocobaltate(III), but six are formed all have structures analogous to 15, with up to three fluorines on the pyridine ring. 

Isoquinoline over cesium tetrafluorocobaltate(III) reacts at 335-340°C to give98 a 40-50% yield of a mixture of at least 10 components the only ones identified being perfluoro(methyl-cyclohexane) and the bicyclodiene 17. 

Considerable differences are evident m the results of fluorinations of toluene with potassium tetrafluorocobaltate at 340 °C [25] and with cesium tetrafluorocobaltate at 320 °C [29] (Table 2)... 

In principle, this would be the preferred route, but in practice no generally successful procedure is available for the synthesis of highly fluorinated compounds directly by this approach. It has been reported that pentafluoro-pyridine may be obtained in approximately 15% yield by fluorinating pyridine over cesium tetrafluorocobaltate (Eq. 10).45 But it appears that... 

Since 10 and pentafluoropyridine are the principal products in the small-scale fluorination of pyridine over cesium tetrafluorocobaltate (Eq. 10), this constitutes an overall direct synthesis of pentafluoropyridine via a very interesting rearrangement. 

Similarly, fluorination of benzofuran 11 with cesium tetrafluorocobaltate(III) led to a mixture of nonaromatic products. Heating the product 12 over nickel gauze at 580 °C yielded hexa- and pentafluorobenzo[ ]furans 14 and 15 [19],... 

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