Trifluorovinyl

HFPO reacts with a large number of acyl fluorides in a general reaction to give 2-alkoxytettafluotoptopionyl fluorides which in turn may be converted to trifluorovinyl ethers (eq. 14). 

Tetrafluoroethylene undergoes addition reactions typical of an olefin. It bums in air to form carbon tetrafluoride, carbonyl fluoride, and carbon dioxide (24). Under controlled conditions, oxygenation produces an epoxide (25) or an explosive polymeric peroxide (24). Trifluorovinyl ethers,... 

A more efficient agent than peroxy compounds for the epoxidation of fluoro-olefins with nonfluonnated double bond is the hypofluorous acid-acetomtrile complex [22] Perfluoroalkylethenes react with this agent at room temperature within 2-3 h with moderate yields (equation 13), whereas olefins with strongly electron-deficient double bond or electron-poor, sterically hindered olefins, for example l,2-bis(perfluorobutyl)ethene and perfluoro-(l-alkylethyl)ethenes, are practically inert [22] Epoxidation of a mixture of 3 perfluoroalkyl-1-propenes at 0 C IS finished after 10 mm in 80% yield [22] The trifluorovinyl group in partially fluorinated dienes is not affected by this agent [22] (equation 13)... 

Higher perfluorovinylic bromides other than trifluorovinyl bromide and pentafluoropropenyl bromide [55] have not been synthesized until recently [42, 54,... 

The reactivity of various groups (R) follows the sequence allyl, benzyl > aryl > alkyl, and usually proceeds readily to the stage of RaSnlOSORlj (121,122), but pentafiuorophenyl- and trifluorovinyl-tin bonds are usually unreactive. The reactivity is enhanced by such ligands as bipyridyl (123). 

Trifluorovinyl Groups. Trifluorovinyl groups have characteristic chemical shifts and coupling constants that are exemplified in Scheme 3.49 (see Chapter 6 for more details and examples). 

The fluorine substituent at the 2-position of a trifluorovinyl group is much more highly shielded than the other two fluorines, and its presence gives rise to an enhanced split of the diastereotopic fluorines at the 1-position and enhanced coupling constants, both geminal and vicinal. 

A typical 19F NMR spectrum of a compound with a trifluorovinyl group is given in Fig. 6.20. This compound is the chemical precursor of the drug known as EF5, which is used in positron emission tomography imaging to detect hypoxic tissue. 

Trifluorovinyl Halides and Ethers. Trifluorovinyl halides are quite commonly encountered reagents, while trifluorovinyl ethers have increased interest as novel monomers.3 There is a nice recent paper dealing with the NMR spectra of some trifluorovinyl ethers.4 Fluorine data for a couple of examples of halides, ethers, and thioethers are given in Scheme 6.30. 

Carbon and Proton NMR Spectra of Trifluorovinyl Compounds. Scheme 6.31 provides the carbon and proton NMR data for a few trifluorovinyl compounds. 

Methyl trifluorovinyl ether, b.p. 10.5- 12.5°C, prepared from tetrafluoroethylene and sodium methoxide [1], has considerable explosive potential. On ignition, it decomposes more violently than acetylene and should be treated with extreme caution [2], Other trifluorovinyl ethers are similarly available from higher alkoxides [1], and although not tested for instability, should be handled carefully. Presence of fluoro-haloalkanes boiling lower than the ether stabilises the latter against spark-initiated decomposition in both fluid phases [3],... 

Dittrich, R. and Hagele, G., Michaelis-Arbuzov perhalogentation reaction of olefins. III. The trifluorovinyl halide, CF2CFX, Phosph. Sulf, 10, 127, 1981. 

J. Ji, S. Narayan-Sarathy, R.H. Neilson, J.D. Oxley, D.A. Babb, N.G. Rondon, and W.S. Jr. Smith, [p-( (Trifluorovinyl)oxy)phenyl]lithium formation, synthetic utility, and theoretical support for a versatile new reagent in fluoropolymer chemistry, Organometallics, 17 783-785 (1998). 

In 1988 Heinze and Burton reported a facile synthesis of various a,p,P-trifluorostyrenes.15 These trifluorostyrene compounds were reported to be unstable to cyclodimerization at room temperature when stored neat, especially the compounds that were /lura-substituted with electron-donating substituents. They described the preparation of one compound, l,4-bis(trifluorovinyl)benzene with the observation that the material gelled when allowed to stand neat overnight. They offered the explanation that the gel was a polymer network connected with flnorinated cyclobutanes. Burton later went on to utilize this dimerization reaction for the cross-linking of polyimide thermoplastics.16... 

This chemistry was also performed on one trisphenol, 1,1,1 -tris(4-hydro-xyphenyl)ethane (THPE). The resulting tris(trifluorovinyl ether) monomer forms a thermoset polymer upon curing. 

Figure 3.3. Synthesis of trifluorovinyl ether monomers and perfluorocyclobutane aromatic ether polymers.

A variety of polymer compositions that use this type of polymerization chemistry can be envisioned. In addition to the polyarylate homopolymers that have been described in this chapter, random or block copolymers can be prepared with reasonable ease by the combination of different monomers or oligomers. These compositions can be designed to optimize thermal, mechanical, dielectric, or optical properties of a polymer system. Also, the trifluorovinyl ether functionality can be incorporated into other high-performance polymer systems with relative ease.34,35 The perfluorocyclobutane polyarylate chemistry is a versatile approach to the preparation of high-performance polymers, which is just beginning to demonstrate its utility. 

The polymerization occurs by ionic addition of OH groups to trifluorovinyl ethers although additions of nucleophiles to fluorinated olefins are well known, few examples of additions to trifluorovinyl ethers have been reported15 and no polymerizations by this method have been described. ... 

We have recently described the high-yield addition reaction of phenols to trifluorovinyl esters as a useful process for other polymer systems. 

After isolation, the intermediate products were reacted with zinc in acetonitrile or a glyme solvent to provide the trifluorovinyl ether monomers. This reaction with zinc is also sensitive to the presence of protic substances in the reaction mixture, and forms the same tetrafluoroethyl ether by-product in an undesirable side reaction. The reaction of the 2-bromotetrafluoroethyl ether reactants with zinc involves the formation of zinc organometallic species as an intermediate, and this species is sensitive to hydrolysis by water or acidic substances (Figure 3.6). 

The reactivity of arylxenonium and alkenylxenonium salts towards iodo compounds in aHF is not yet reported although perfluoroalkynylxenonium tetrafluoroborates show excellent alkynylating properties in reactions with alkyl, trifluorovinyl, pentafluorophenyl, and 3-fluorophenyl iodides (eq 19) (49). 

The Cope rearrangement mechanism can be also strongly affected by other substituents. Thus, the normal electrocyclic process in the thermal isomerization of divinyl aromatics has been suppressed relative to the thermolysis of l,2-bis(trifluorovinyl)naphthalene 438 (in benzene, at 193 °C, 24 h)231. Three major products 440-442 were isolated from the reaction mixture, but none of them was the expected product 439. Also formed in low... 

Partially fluorinated PEMs based on trifluorostyrene and a trifluorovinyl ether derivative. 

Trifluorostyrene-based monomers and fheir derivatives are known to exhibit dimerization preferentially over polymerization in confrasf to fhe hydrocarbon analogue slyrene. Eord, DesMarfeau, and Smifh, Smifh and Babb,i i and Smith et al. have advantageously used this behavior to produce 6 (where E can be a large number of differenf spacer groups buf also typically be sulfonamide-based) via cyclopolymerization of multifunctional monomers bearing at least two trifluorovinyl ether units. The polymers themselves have perfluorocyclobutane (PFCB) rings as part of the main chain. 

Perpall, M. W., Smith, D. W., Jr., DesMarteau, D. D. and Greager, S. E. 2006. Alternative trifluorovinyl ether derived fluoropolymer membranes and functionalized carbon composite electrodes for fuel cells. Journal of Macromolecular Science Part C Polymer Reviews 46 297-313. 

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