Niobium V Fluoride

Powdered niobium metal, 20.0 g. (—200 mesh), and tin(II) fluoride, 52.0 g. (40 mesh),t are mixed in a molybdenum crucible in an Inconel- or nickel-pipe reactor approximately 3 in. in diameter and 10 in. long and heated to 400-500°C. in a stream of dry nitrogen. The niobium(V) fluoride volatilizes from the reaction mixture and condenses on the water-cooled lid of the reactor, which leaves metallic tin in the crucible. The yield of niobium(V) fluoride is 21.1 g., or 95% of theoretical. A very small amount of blue niobium oxyfluoride (composition of variable oxygen and fluorine content) often forms as an impurity because of the presence of minute amounts of oxygen. Anal. Calcd. for NbFs Nb, 49.44 F, 50.56. Found Nb, 49.43 F, 50.2. 

The white crystalline solid is very hygroscopic and has an m.p. of 80°C. andab.p. of235°C. 

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Pentafluorocthyl iodide is of practical interest, particularly as a precursor of higher perfluoroal-kyl iodides. There are several patents for the preparation of the key compound from tetra-fluoroethene, iodine pentafluoride and iodine at 75-80 C in the presence of catalysts anti-mony(III) fluoride, titanium(lV) chloride, boron trifluoride, vanadium(V) fluoride, niobium(V) fluoride, and molybdenum(Vl) fluoride.11-13 The agents iodine monofluoride" and bromine monofluoride" can add to branched pcrfluoroalkcnes, e.g. perfluoro-2-methylbut-2-ene gives perfluoro-2-iodo-2-methylbutane.1415... 

Finally, a patent from DuPont claims that compound 19 and l,l-dichloro-t,2,2-lri-fluoroethane (CCI2FCHF2) can both isomerize to give the trifluoromcthyl derivative 20 in the presence of tantalum(V) fluoride or niobium(V) fluoride,10... 

Perfluorocyclohexa-1,3-diene (3) and perfluorocyclohcxa-1,4-diene (4) have been equilibrated with antimony(V) or niobium(V) fluoride to an 8 92 mixture in favor of the nonconjugated 1,4-isomer 4.3,36 Similar results with the use of a fluoride ion are discussed at the end of this section. 

The compound niobium tetrafluoride is of importance because of the increased interest in reactions of metal tetrafluorides with basic ligands. Previous syntheses given for this compound are time consuming, generally cannot be scaled up to prepare larger quantities, or require expensive equipment not always readily available. In this synthesis, simple methods are described for the preparation of niobium(V) fluoride and niobium(IV) fluoride, which should make these compounds readily available to chemists for further comparison studies with other metal tetrafluorides. 

The following preparative method (of general utility) includes the reduction of niobium(V) fluoride with elements such as silicon, phosphorus, and boron,1 which yield highly volatile fluorides. Silicon reductions have been studied in greatest detail. Niobium(IV) fluoride can be prepared in good yield by the reaction described by the equation ... 

If niobium(V) fluoride is purchased from commercial vendors, it must be purified by sublimation before use. Charges of niobium(V) fluoride (5-50 g. in a platinum crucible) are heated in... 

In a typical experiment, 4.63 g. (0.025 mole) of niobium(V) fluoride is mixed with 0.348 g. (0.012 mole) of -200-mesh silicon and loaded into the reactor inside a glove box under dry nitrogen. The assembled reactor is connected to a helium tank and repeatedly pressurized and depressurized to rid the system of air. The entire system is pressurized to 50 p.s.i., the Monel reactor valve is closed, and the reaction chamber is placed in a vertical furnace at 350°C. The pressure in the external lines is left at 50 p.s.i. to prevent entry of air. 

Nickel(IV) sodium paraperiodate 1-hydrate (amt.) analysis of, 6 203 Nickel tetracarbonyl, 2 234 Niobium(V) fluoride, 3 179 Nitramide, 1 68, 72 Nitrates, preparation of anhydrous, 5 38... 

F4Si Silicon tetrafluoride, 4 145 FeBr Bromine (V) fluoride, 3 185 F6Nb Niobium(V) fluoride, 3 179 F6Ta Tantalum (V) fluoride, 3 179 F6GeBa Barium hexafluorogerma-nate(IV), 4 147... 

NaNj Sodium azide, 1 79 2 139 NaOCSodium butoxide, 1 88 NaOj Sodium superoxide 4 82 Na202-8H20 Sodium peroxide, 3 1 NbFt Niobium (V) fluoride, 3 179 NdClj Neodymium chloride, 1 32 Nd2(C2O4)2 10H2O Neodymiumox-alate, 2 60... 

The reactivity of halogenated alkenes in the electrophilic hydrofluorination reaction decreases with an increasing number of halogen atoms. Thus polyhaloalkenes are rather resistant to the electrophilic addition of hydrogen fluoride.Therefore, the hydrofluorination needs catalysis, with boron trifluoride(Table 6), tantalum(V) fluoride (Table 5), antimony(V) chloride, niobium(V) fluoride,titanium(IV)chloride or molybdenum(V) chloride. ... 

Indeed, in a recent patent, phosgene was used as a drying agent in this reaction, for the syntheses of niobium(V) fluoride and tantalum(V) fluoride [1481a]. COF can provide a completely anhydrous route to these compounds, generating CO, instead of water as the co-product (see Section 13.13.2) ... 

Na202-8H20 Sodium peroxide, 3 1 NbF5 Niobium(V) fluoride, 3 179 NdCl3 Neodymium chloride, 1 32 5 154n. 

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