Tetrafluoroethene, 413 Table

Many perfluoroaUphatic ethers and tertiary amines have been prepared by electrochemical fluorination (1 6), direct fluorination using elemental fluorine (7—9), or, in a few cases, by fluorination using cobalt trifluoride (10). Examples of lower molecular weight materials are shown in Table 1. In addition to these, there are three commercial classes of perfluoropolyethers prepared by anionic polymerization of hexafluoropropene oxide [428-59-1] (11,12), photooxidation of hexafluoropropene [116-15-4] or tetrafluoroethene [116-14-3] (13,14), or by anionic ring-opening polymeriza tion of tetrafluorooxetane [765-63-9] followed by direct fluorination (15). 

Fluorinated alkenes tend to be pulmonary irritants, but most of the commercially important alkenes, such as tetrafluoroethene (TFE) and hexafluoropropene (FIFP), are only slightly toxic (Table 5). 

Table 3. Reaction of Tetrafluoroethene with an Oxidizing Agent and Catalysl...

Table 6. Coproportionation of Tetrafluoroethene with 1 J-Diehloro-2.2-difluoroethcne...

The UPS of the haloethenes was reviewed by Wittel and Bock in Supplement D of this Series4. The haloethenes for which UPS data are available constitute less than half of the 174 compounds which can be made by substituting different combinations of H, F, Cl, Br and I atoms on the C=C bond. However, the valence electronic structures and the nature of the ncc orbitals appear to be well understood. Nonetheless, if the past be any guide, some unexpected results will turn up. Thus, tetrafluoroethene was among the first compounds in which a perfluoro effect was observed. The TS interaction between fluorine atoms was discovered in ds,-difluoroethene. Some data for haloethenes and allyl halides are given in Table 6. 

For cyclodimerization of fluoroalkenes to occur the alkencs must contain at least two geminal fluorine atoms, for example, tetrafluoroethene(l), trifluoroethenes, substituted trifluoroethenes, and l,l-dihalo-2.2-difluoroethene. These reactions require high temperatures and pressures. When the alkene is unsymmetrical. as in the case of l,l-dichloro-2,2-difluoroethene (3), two diflPerent orientations of addition can be envisaged to occur, hcad-to-head addition and head-to-tail addition,Generally, only the head-to-head adducts and not the head-to-tail adducts arc formed under kinetic control (Tabic 3, see also Houben-Wcyl, Vol. E17e, p85 however, see Table 3 and Houben-Weyl, Vol. 5/3. p 250 for rare examples of accompanying head-to-tail adducts). 

The addition of phosphanes to fluoroalkenes follows a free-radical mechanism. For example, tetrafluoroethene (1) yields preferentially the linear addition product 2 in moderate yield when reacted with phosphane at 150 C (see also Table 6). ... 

The reaction of fluoro- or chlorofluoroalkenes with the sulfur tetrafluoride/hydrogen fluoride/ sulfur monochloride system leads to perfluoroalkanesulfenyl chlorides, (sulfanyl)sulfenyl chlorides, sulfides and polysulfides.511 514 Tetrafluoroethene reacts with sulfur tetrafluoride/hydrogen fluoride in the presence of 1 equivalent of sulfur monochloride at 80°C to yield a mixture of pentafluoroethanesulfenyl chloride (4), (pentafluoroethanesulfanyl)sulfenyl chloride (5) and bis(pentafluoroethyl) trisulfide (6).513 Other examples of this type of reaction are summarized in Table 37. 

Carbonyl difluoride is the principal product of the oxidation of tetrafluoroethene by molecular oxygen, whether induced thermally, photolytically, or by ionizing (X-ray or y-ray) radiation. A comparison of the methods has been carried out for the gas phase in a static system, and the results are summarized in Table 13.2 [320]. Tetrafluoroethene oxide, CjF O (13.2), and hexafluorocyclopropane, (CF2)3 (13.3), are formed as additional gaseous products... 

Photochemical decomposition of diazo(trimethylsilyl)methane (1) in the presence of alkenes has not been thoroughly investigated (see Houben-Weyl Vol. E19b, p 1415). The available experimental data [trimethylsilylcyclopropane (17% yield) and la,2a,3j8-2,3-dimethyl-l-trimethylsilylcyclopropane (23% yield)] indicate that cyclopropanation occurs only in low yield with ethene and ( )-but-2-ene. In both cases the formal carbene dimer is the main product. In reactions with other alkenes, such as 2,3-dimethylbut-2-ene, tetrafluoroethene or hexafluoro-propene, no cyclopropanes could be detected.The transition-metal-catalyzed decomposition of diazo(trimethylsilyl)methane (1) has been applied to the synthesis of many different silicon-substituted cyclopropanes (see Table 3 and Houben-Weyl Vol.E19b, p 1415) 3.20a,b,2i.25 ( iQp. per(I) chloride has been most commonly used for carbene transfer to ethyl-substituted alkenes, cycloalkenes, styrene, and related arylalkenes. For the cyclopropanation of acyl-substituted alkenes, palladium(II) chloride is the catalyst of choice, while palladium(II) acetate was less efficient, and copper(I) chloride, copper(II) sulfate and rhodium(II) acetate dimer were totally unproductive. The cyclopropanation of ( )-but-2-ene represents a unique... 

Write an equation representing the synthesis of Teflon from tetrafluoroethene. (Hint Refer to Table 12.1.)... 

In example 3 in Table 6.9, the [2 -i- 2] addition reaction of 1,1,2,2-tetrafluoroethene to both the double and triple bonds of but-3-en-l-yne (vinylacetylene, HOC-CH=CH2) is shown. Both addition reactions appear to occur with about equal facility (a 1 1 mixture is obtained) and the process may involve free radicals. 

---