Fluorine exchange

When used with antimony pentachloiide, the reactivity of HF is comparable to SbCl2F2 alone. Therefore a continuous fluorination exchange process is possible where antimony is the fluoride carrier from FIF to the organic fluoride. 

Another example of a simultaneous chlorine-fluorine exchange and rearrangement IS the reaction of orr/io-methylphenylchloroformate with hydrogen fluoride to give a stable tetrafluorobenzodioxtn [34] (equation 25)... 

Triethylbenzylammonium chloride and potassium fluoride containing 1% water can provide chlorine-fluorine exchange of activated halides in the absence of a solvent. This mixture also can displace the chlorine of a chlorodifluoromethyl group to form a trifluoromethyl group [62] (equation 36). 

Another point of contention has been the extent to which, if any, SbFj is reduced to SbFs upon intercalation. Although chemical analyses have shown an F Sb ratio of 5 1 (Lll, M5), Sb Mossbauer measurements (B24) indicated partial reduction of Sb(V) to Sb(III). On the other hand, mass-spectral measurements as a function of temperature (S15) showed only SbFs, evolved in stages, with no fluorocarbons emitted at any time. The latter are usually an indication of partial reduction of the intercalant and fluorination of the graphite host. Wide-line, F-NMR chemical-shifts are consistent with either SbFj or SbFe, but not with SbFs, but the occurrence of fluorine exchange could produce minor amounts of trivalent species (FI 1) this point is thus still controversial, and will be alluded to again. 

The main product of the reaction was CF2=CHC1. Moreover, two secondary alkenes CFC1=CHC1 (Z and E) were formed from CF2 = CHCl by successive chlorine-fluorine exchanges [10], After a fast initial deactivation, the catalyst stabilized. The catalytic activity for the dehydrofluorination reaction was estimated after a 5 hours reaction from the sum of the amount of alkenes. 

F and 119Sn NMR. Fluorine exchange occurs 165 between 4- and 5-coordinated tin complexes, possibly through chlorine and fluorine-bridged species. 

Solutions of SeF4-BF3 in HF are considered to contain an equilibrium mixture as shown in Eq. (3), involving a dimer (SeF4-BF3)2 with some additional fluorine exchange mechanism involving SeF3 and BF3. 

Gillespie, R. J., Hartman, J. S., Parekh, M. Solvent Effects on the Boron-Fluorine Coupling Constant and on Fluorine Exchange in Tetrafluoroborate Anion. Can. J. Chem. 46, 1601 (1968). 

This indirect proof of the appearance of CF3SF leads to the conclusion that fluorination of sulfenyl chlorides of the series CF Cl3 SCl (n = 0, 1, 2) with alkali metal fluorides follows the mechanism observed in the formation of sulfenyl fluorides the initial chlorine-fluorine exchange at the sulfur atom is followed by isomerization to the sulfenyl chloride containing the corresponding more highly fluorinated methyl group. 

The introduction of the perfluorohalogenosulfenyl group into aromatic compounds was accomplished long before the preparation of sulfenyl halides. The CFgS-subBtituted compounds have been synthesized largely by chlorination of the side chain in arylmethylthioethers followed by chlorine-fluorine exchange. This method was applied for the first time in the synthesis of trifluoromethylmercaptobenzene 92, 140, 172) ... 

Penta-coordinated fluorophosphoranes have been extensively considered by Schmutzlera965,12andl4) and discussed in detail in ref. 1966, 1, p. 281 seq. The special interest was in the existence of two well-defined types of fluorine substituents, as well as for the hexa-coordinated (PVI)e compounds. Fluorine exchange generally occurs by pseudorotationf but steric hindrance, substituent conjugation and low temperatures may stabilize fluorine atoms in their respective position. As a rule (see Section... 

Sulphur fefra[ F]fluoride (S[ F]F4) was obtained by irradiation of a neon-SF4 mixture, giving rise to a low-specific-activity product by fluorine-18 for fluorine exchange. It was used as an alternative to H[ F]F in the preparation of [ F] DAST [57], S[ F]F4 has not found other applications so far. 

The halogen-fluorine exchange with an HF-amine complex allows the transformation of a gem-dichloro goup into a difluoro group. While this reaction is difficult to initiate in nonactivated positions, it is efficient in the benzylic position and in the a position of functional groups (e.g., esters, phosphonates) (Figure 2.10). ... 

Examples of kinetic analysis of NMR spectra in the transition between slow and fast exchange (on the NMR time scale) are somewhat limited. Treatment of fluorine exchange in sulfur tetrafluoride is selected here because this exchange process exemplifies the type of kinetic process ideally suited to NMR study. The fluorine atoms of the two nonequivalent environments in this molecule of C2v symmetry give rise to two triplets under conditions of very slow exchange at temperatures below —85° (at 40 Mc/sec). 

Fig. 17. Determination of Ea and vn for fluorine exchange in SF4 where here is the frequency factor and S is the chemical shift in cps. [Muetterties and Phillips (89).]...

Furthermore, the halofluorination method can also be modified to prepare vicinal difluorides by a one-pot two-step reaction. Halofluorination followed by nucleophilic halogen-fluorine exchange is carried out simply by adding silver(I) fluoride to a solution of the initially formed a-fluoro-/J-haloalkanes, effecting the exchange in situ202 203 (Table 12). 

Bromine trifluoride is used to selectively substitute fluorine for bromine in brominated alkanes and esters. The reactions are carried out by gradual addition of bromine trifluoride to a solution of the substrate in CFC-113 or CFC-112 at 10-20nC. The bromine-fluorine exchange in mono-bromohaloalkanes is nonstereoselective and accompanied, in some eases, by skeletal rearrangements, hydride shifts, and halogen migrations. All three fluorine atoms in bromine trifluoride are involved in the fluorination reaction. Chlorine atoms in the substrate molecules remain intact.109... 

Selective bromine-fluorine exchange of one bromine atom occurs in the reaction of tram-4,5-dibromo-m-cyclohexane-1.2-dicarboxylic anhydride (10) with sulfur tetrafluoride to give isomers of 5-bromo-l,l,3.3,7-pentafluoro-c/.v-octahydroisobenzofuran (11) and 4-bromo-5-fluoro-m-1.2-bis(trifluoromethyl)cyclohexane (12) in a 5 1 ratio and good total yield.11... 

Chlorine fluorine exchange between alkyl- or arylehloroboranes and antimony(Ill) fluoride proceeds very readily with evolution of heat. The compounds listed in Table 2 have been obtained by this reaction. 

Table 2. Chlorine Fluorine Exchange between Alkyl- or Arylchloroboranes and Antimony(III) Fluoride...

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