Vanadium V fluoride

Pentafluorocthyl iodide is of practical interest, particularly as a precursor of higher perfluoroal-kyl iodides. There are several patents for the preparation of the key compound from tetra-fluoroethene, iodine pentafluoride and iodine at 75-80 C in the presence of catalysts anti-mony(III) fluoride, titanium(lV) chloride, boron trifluoride, vanadium(V) fluoride, niobium(V) fluoride, and molybdenum(Vl) fluoride.11-13 The agents iodine monofluoride" and bromine monofluoride" can add to branched pcrfluoroalkcnes, e.g. perfluoro-2-methylbut-2-ene gives perfluoro-2-iodo-2-methylbutane.1415... 

The fluorination of polyfluorocyclohexenes with antimony(V) fluoride proceeds under much more severe temperature conditions ( 150 C) than with vanadium(V) fluoride (see Section 12.4.2). In these reactions antimony(V) fluoride effects both the oxidative addition of fluorine and the substitution of vinyl chlorine atoms by fluorine.48... 

Vanadium(V) fluoride (mp 19 C. bp 47.9 C) is prepared by treating vanadium with fluorine gas in a nickel flow reactor. Prior to use, vanadium(V) fluoride should be distilled over sodium fluoride in a nickel or stainless steel apparatus.113... 

Vanadium(V) fluoride converts polyfluoroaromatics into fluorinated cyclohexadienes and cyclohexenes, and reacts with polyfluorinated and polychlorinated alkenes,113 115 alkadienes, cycloalkenes and cyclodienes to give addition products of two fluorine atoms across C = C bonds.116117... 

The reaction of compounds C6F5R with vanadium(V) fluoride at — 25 to — 30 C in sulfuryl chloride fluoride or trichlorofluoromethane solution yields 1-substituted heptafluorocyclo-hexadienes and nonafluorocyclohexenes with the former predominating (see Table 5).113-115... 

When R = Me, first one or two hydrogen atoms of the methyl group are substituted by fluorine. Methyl groups attached to the C = C bond in the cyclohexadiene or cyclohexene are almost unreactive towards vanadium(V) fluoride under the indicated conditions, but at 25 C a mixture of products from C = C bond fluorination and substitution of hydrogen in the methyl group is formed.117... 

When treated with vanadium(V) fluoride, decaf]uorobiphenyl adds 2 to 8 fluorine atoms. Octafluoronaphthalcne reacts with vanadium(V) fluoride in the molar ratio of 1 2.5 to produce four addition products containing 2 to 6 extra fluorine atoms, with a total conversion of 100%. 

Fluorination of fluoroalkenes with terminal C = C bonds with vanadium(V) fluoride proceeds readily at —30 to — 25 C in trichlorofluoromelhane solution. The only reaction products are the corresponding polyfluoroalkanes formed in high yields.117... 

With excess vanadium(V) fluoride, the products of further fluorination of the aromatic ring are formed. 

Polyhaloalka-1,3-dienes are fluorinated with vanadium(V) fluoride under the same conditions as used for terminal alkenes. The reaction of 2-chloropentafluorobuta-1,3-diene (3) proceeds chiefly by the 1,4-addition mechanism. 

Treatment of perchlorobula-1,3-diene with vanadium(V) fluoride at —25 C leads to hexa-chloro-l,2,3,4-tetrafluorobutane and hexachloro-l,1.2,4-tetrafluorobulane in nearly equal yields (Table 6). 

The reactivity of polyfluorinated cycloalkenes towards vanadium(V) fluoride is similar to that of internal alkenes (Table 7). Perfluorocyclobutene (4) reacts with vanadium(V) fluoride at 20-22 C however, at 50-60 C the fluorination proceeds more efficiently. 

The relative fluorination rates for nonequivalent C = C bonds in substituted perfluorocyclo-hexa-1,4-dienes depend on the electronic properties of the substituents and indicate the electrophilic nature of vanadium(V) fluoride."4... 

Fluorinations with Vanadium(V) Fluoride General Procedures 17... 

Vanadium(V) fluoride was reported to react with dichloromethane to give a mixture of chlorofluoromethane, dichlorofluoromethane, and chlorodifluoromethane.119... 

Great differences in product structures and product distributions are obtained by lead(IV) oxide or acetate oxidation of perfluorophenol in different solvents and media. The reaction with the former agent gives a quinoid ether in 22% yield (Table 10).173 The oxidation with lead(IV) acetate has been optimized to such a level as to give perfluoro cyclohexa-2,5-dienone (4) in 65 % yield.174 Treating the phenol with vanadium(V) fluoride or vanadium(III) fluoride as well as xenon difluoride gives a mixture of products,175 therefore, the reactions are only of minor preparative importance. 

Polyhaloalkenes can be fluorinatcd with vanadium(V) fluoride. Terminal polyfluoroalkencs react at between — 20 and — 30 C, while internal polyfluoroalkenes are fluorinated at 40 to 150 C. Table 15 lists some examples. 

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