Migration of fluorine

Lewis acids promote migration of fluorine m halofluoroalkenes to yield isomers, which can be transformed easily into perfluorinated alkynes [27. 22] (equation 6)... 

The driving force of the reaction is the formation of a more stable radical, i.e. the unpaired electron is delocalised more effectively by Q in (1276) than by H in (127a). Migration of fluorine does not occur as its d orbitals are not accessible, and migration of Br only rarely as the intermediate radicals undergo elimination (to alkene) more readily than rearrangement. 

Intramolecular migration of fluorine and chlorine atoms is described in Section 5. The rearrangement of fluorine and chlorine atoms likewise can occur intermolecularly between a number of chlorofluorocarbon molecules. This disproportionation (dismutation) takes place catalyti-cally or thermally. With aluminum trichloride as a catalyst, for example, enrichment of the fluorine atoms takes place in one molecule 1 and enrichment of the chlorine atoms in the other 2. 

The reaction of fluorohaloethanes with catalytic amounts of aluminum chloride or, better still, aluminum bromide, is peculiar to fluorohaloal-kanes and alkenes. It is the migration of fluorine and other halogens to accumulate fluorine on one carbon [133]. 

This ease of migration of fluorine from carbon to boron has inhibited the development of hydroboration techniques in fluorinated systems. However, when the carbon-fluorine bond is sufficiently remote from the boron, then hydroboration works well and Markov-nikov or anti-Markovnikov additions may be obtained, depending on the hydroborating system dicyclohexylborane, (Chx)2BH, is less electrophilic but sterically more demanding than dihaloboranes (Figure 10.25). 

However, two pentafluorophenylaluminium derivatives, 10.35A and 10.35B, have been isolated [85] by cleavage of the mercurial (Figure 10.35). Both 10.35A and 10.35B eventually explode violently on heating and this occurs with 10.35A at about 195° C. Nevertheless, the relative stability of these uncomplexed fluorocarbon derivatives may be attributed to bromine bridging, which saturates the covalency of aluminium and inhibits migration of fluorine from carbon to aluminium. Evidence from NMR spectra indicates either stmcture shown in Figure 10.36 for compound 10.35A. 

These experiments with water vapor exposure also confirm that the decrease of fluorine atoms observed by XPS is indeed mainly due to the migration of fluorine-containing segments away from the top surface region because no washing can occur in these experiments. 

Cesium fluoride as fluoride ion catalyst Migration of fluorine Perfluoro compounds... 

Woods et al. [95] have studied the influence of the fluorocarbon-based polymer processing additive (PEA) Dynamar FX 9613/5920A on the surface and optical properties of polyolefin plastomer blown film by means of XPS and SSIMS. The same techniques were used to study the effect of Dynamar FX 9613 on the surface properties of HDPE [96]. Migration of fluorinated processing aids in HDPE film was also studied by XPS and ATR-FTIR [97]. Lens et al. [98] have reported an XPS study of the orientation of molecules of anionic surfactants, such as... 

Gas-phase photolysis of the cyclic ketones CFa-(CFj) CF,-C 0 x = 2—5) at 3130 A does not involve migration of fluorine atoms, and the products can be explained on the basis of the general Scheme 11. Reactions 1 and la are the only ones of importance for perfluorocyclopentanone and perfluorocyclohexanone (c/. photolysis of perfiuorocyclobutanone to per-fluorocyclopropane and carbon monoxide ), and reactions 3a and 3b are important only for perfluorocyclo-octanone. 

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