Tetrafluoride, fluorine exchange

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). 

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... 

Trifluorodi(phenyl)-/.5-stibane (4) and difluorotri(phenyl)-25-stibane (6) arc less reactive in the chlorine-fluorine exchange.104 They are obtained by reacting diphenylstibinie acid (3) and triphenylstibane oxide (5) or triphenylbis(trifluoroaeetoxy)-A5-stibane (7) with sulfur tetrafluoride.105... 

Rhenium oxide tetrafluoride and rhenium oxide pentafluoride can be used as selective fluorination agents reacting with CH2C12 by chlorine-fluorine exchange with > 90% selectivity and, in the case of ReOF5, subsequent decomposition of the unstable Revu chloride species results in ReOCl4 [348]. 

Intramolecular Processes. Two studies of axial-equatorial exchange in sulphur tetrafluoride have been published. Provided that the sulphur tetrafluoride is carefully purified it is claimed that the data are in good agreement with the Berry pseudorotation mechanism. The presence of impurities readily leads to intermolecular fluorine exchange. It has been claimed that the rate of exchange (in the absence of hydrogen fluoride) is the same in the liquid phase ( =11.2 kcal mol 0 as in the gas phase (E a =11.7 kcal mol ). 

The standard synthesis method features side-chain chlorination of a methylpyridine (picoline), followed by exchange-fluoriaation with hydrogen fluoride or antimony fluorides (432,433). The fluoriaation of pyridinecarboxyHc acids by sulfur tetrafluoride (434) or molybdenum hexafluoride (435) is of limited value for high volume production operations due to high cost of fluorinating agent. 

Qua.driva.Ient, Zirconium tetrafluoride is prepared by fluorination of zirconium metal, but this is hampered by the low volatility of the tetrafluoride which coats the surface of the metal. An effective method is the halogen exchange between flowing hydrogen fluoride gas and zirconium tetrachloride at 300°C. Large volumes are produced by the addition of concentrated hydrofluoric acid to a concentrated nitric acid solution of zirconium zirconium tetrafluoride monohydrate [14956-11-3] precipitates (69). The recovered crystals ate dried and treated with hydrogen fluoride gas at 450°C in a fluid-bed reactor. The thermal dissociation of fluorozirconates also yields zirconium tetrafluoride. 

Impure plutonium oxide residues are dissolved in 12M HN03-0.1M HF under refluxing conditions, and then the plutonium is recovered and purified by anion exchange. Plutonium is leached from other residues, such as metal and glass, and is also purified by anion exchange. The purified plutonium eluate from the anion exchange process is precipitated with hydrogen peroxide. The plutonium peroxide is calcined to the oxide, and the plutonium oxide is fluorinated. The plutonium tetrafluoride is finally reduced to the metal with calcium. 

The exchange of halogen for fluorine with sulfur tetrafluoride, due to the high temperatures generally required, is of limited use. Carbon tetrachloride and carbon tetrabromide react with sulfur tetrafluoride at 225-325 C to give mixtures of halofluoromethanes, while hexachloro-ethane under similar conditions gives l,1.2,2-tetrachloro-l,2-difluoroethane (59%) as the main product.191... 

Reactive chlorine atoms attached to phosphorus and sulfur are easily exchanged for fluorine with sodium fluoride. An easy and efficient method of preparing sulfur tetrafluoride in large quantities is the reaction of sulfur dichloride with an excess of sodium fluoride suspended in acetonitrile.10 Further examples are found in ref 11. 

Halogen exchange reactions, too, are valuable sources of fluorinated pyrimidines, especially 2-, 4-, and 6-fluoro derivatives. Sources of fluoride ion have included hydrogen, sodium, potassium, cesium, antimony, silver fluorides, and sulfur tetrafluoride. All of the reactions required heating. Prepared from nucleophilic fluorination processes have been... 

Probably the most versatile reagent for one-step exchange of hydroxy groups by fluorine, and for many other conversions, is sulfur tetrafluoride SF4 [125]. Sulfur tetrafluoride first converts the alcohol into a covalent intermediate with a nucleofugic group which is subsequently replaced by a liberated fluoride ion, with inversion (S>j2 mechanism). The sulfur tetrafluoride is converted into sulfonyl fluoride, only two fluorine atoms are used for the reaction. 

The mass spectrum is known (78) and there is only one nmr line for fluorine in the nmr spectrum of thionyl tetrafluoride at room temperature (79). This probably means that there is a rapid exchange of fluorine atoms within the molecule. 

Conversion of uranium dioxide to tetrafluoride in contact with hydrofluoric acid Production of caustic alkalis, particularly in the presence of sulfur compounds Reactor vessels and heat-exchanger tubing used in the production of vinyl chloride Process equipment used in the production of chlorinated and fluorinated hydrocarbons... 

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