Fluoro-olefins reaction with radicals

The fraction of head-to-head linkages in the poly(fluoro-olefms) increases in the series PVF2 < PVF PVF3 (Tabic 4.2). This can be rationalized in terms of the propensity of electrophilic radicals to add preferentially to the more electron rich end of monomers (i.e, that with the lowest number of fluorines). This trend is also seen in the reactions of trifluoromethyl radicals wilh the fluoro-olefins (see 2.3). 

Other publications consider the photochemical reactions of Hg(SiMe3)2 with fluoro-olefins, the photo-induced reaction of Me SiCl4 (n = 1—3) with S02Cl2, the e.s.r. properties of photochemically produced substituted triarylsilyl radicals,and a comparison of the phosphorescence spectra of SiPh4, GePh4, SnPh4, and... 

The behavior of methyl and halomethyl radicals in their reactions with the fluoro-olefins (Table 1.2), can thus be rationalized hi terms of a more dominant role of polar factors and the nucleophilic or electrophilic character of the radicals involved. Methyl radicals are usually considered to be slightly nucleophilic, trifluoromethyl and trichloromcthyl radicals arc electrophilic (Tabic 1.4). 

Chlorofluoroalkane formation via free-radical or cationic reactions of fluoro-olefins is dealt with on pages 82 and 67 the conversion of the CCU-CFsrCFCl telomers CQs [CFs CFa] a (1 < x < 5) into Q-[CFCl CFsli COzH (with 20% oleum at 140 °C) and HOzC-CFz [CFCFCFzlx-i COzH via reaction with oleum at 200 Cor treatment with AICI3 to give CCls [CFz CFClJai-i CFz-Caa followed by hydrolysis with oleum at 140 °C) is mentioned later (p. 154). ... 

Free-radical Reactions.—number of further publications have appeared concerning the free-radical insertion of fluoro-olefins into C—H bonds (see Voi. 2, p. 122). Perokide-initiated reaction of toluene, and other alkyl benzenes having benzylic hydrogens, with hexafluoropropene yields mainly the adduct (89) and some of the indane (90) arising from cyclization of the initially formed radical, with subsequent dehydrogenation. The indane (90) yields the corresponding indene with ethanolic... 

Since no evidence for an initial cfj-isomer could be obtained, a transoid free-radical addition was preferred to a four-centre mechanism. No fluoro-trimethylsilane was formed in this reaction, which precludes the occurrence of the addition-elimination sequence proposed for reactions of the mercurial with fluoro-olefins. Perfluoropropyne behaves differently and its reaction with the mercurial yields mainly the substitution product 3,3,3-trifluoro-l-trimethylsilylpropyne (86%), an almost equal amount of fluorotrimethyl-sitane, and only 5% of a disilylpropene, CFa C SiMe3) CF SiMcs. The latter product was also obtained by treating hexafiuoropropene with the mercurial, but its geometry could not be firmly established and further developments are awaited to resolve the interesting mechanistic possibilities. 

It is apparent that substitution of fluorine for hydrogen initially causes a reduction in reactivity towards the electrophilic oxy n atom, but tetra-fluoroethylene is anomalous. A further study has indicated that substitution by trifluoromethyl has a strong deactivating effect compared with methyl, which has an activating effect. A study of the reactions of nearly thermal i F atoms, produced by F(n,2n) F and moderated by collisions with an excess of sulphur hexafluoride, with fluoro-oleflns (modes of addition were identified by scavenging the radicals produced with hydrogen iodide) has indicated that F atoms react preferentially with less-fluorinated olefins, and at the less-fluorinated end of a particular olefin. ... 

---