Alkali-metal fluorides

Several alkali metal fluoride complexes withXeOF are known, such as 3KF XeOF [12186-19-5], 3RbF -2K.eO [12186-23-1], CsF XeOF ... 

More general procedures for additions of halogen fluorides to highly fluori-nated olefins involve reactions with a source of nucleophilic fluoride ion, such as an alkali metal fluoride, in the presence of aposttive halogen donor [62 107, lOff, 109, 110, 111] (equations 11 and 12) These processes are likely to occur by the generation and capture of perfluorocarbamonic intermediates Tertiary fluormated carbanions can be isolated as cesium [112], silver [113], or tns(dimethylamino)sul-... 

Hypochlorites- are obtained by reaction of fluorinated carbonyl compounds, such as carbonyl lluonde, with an alkali metal fluoride and chlorine fluoride f62, 720]... 

With nitriles, products from addition of one or two equivalents of halogen fluoride can be obtained [725, 726, 127, 128] (equations 25 and 26) on reaction with chlorine fluoride or bromine and an alkali metal fluoride. 

Fluorinated tertiary selenoetheis are prepared by reaction of branched per-fluoroolefins with an alkali metal fluoride and phenylselenenyl chloride 1S2] (equation 31)... 

When potassium fluoride is combined with a variety of quaternary ammonium salts its reaction rate is accelerated and the overall yields of a vanety of halogen displacements are improved [57, p 112ff. Variables like catalyst type and moisture content of the alkali metal fluoride need to be optimized. In addition, the maximum yield is a function of two parallel reactions direct fluorination and catalyst decomposition due to its low thermal stability in the presence of fluoride ion [5,8, 59, 60] One example is trimethylsilyl fluoride, which can be prepared from the chloride by using either 18-crown-6 (Procedure 3, p 192) or Aliquot 336 in wet chlorobenzene, as illustrated in equation 35 [61],... 

The use of cesium fluoride is limited because of its cost and its availability as a truly anhydrous reagent. Its use with 18-crown-6 shows a 5 times higher rate for the formation of benzyl fluoride from benzyl bromide when compared with cesium fluonde or potassium fluoride supported on calcium fluoride [21] Either cesium fluoride or potassium fluoride supported on calcium fluoride (Procedures 5a and 5b, p 194) provides about a twofold improvement over either unsupported alkali metal fluoride [55, 69], Cesium fluoride and Aliquat 336 convert benzyl bromide to the fluoride in 94% yield. Using tetrabuty lammonium fluoride in place of Aliquat... 

An alternative route to the reaction of mercuric fluoride with fluoroolefins in liquid hydrogen fluoride [154] was developed during the early and middle 1970s This improved method involved the reaction of fluoroolefins and mercury salts in the presence of alkali metal fluorides m aprotic solvents [i5J, 156] (equation 118)... 

A similar distribution of copper reagents can be obtained via the du ect reaction of copper metal with dibromodifluoromethane or bromochlorodifluoromethane in DMF at 85-95 °C [2J2] The oligomerization can be supressed via the addition of alkali metal fluorides to the reaction mixture [272] When HMPAis added to the trifluoromethylcopper solution, decomposition is slowed, and this solution can be used to trifluoromethylate aromatic iodides [270] (equation 143). 

Systematic investigations of the compounds that can be precipitated by adding alkali metals fluorides to HF solutions containing tantalum or niobium are discussed in [60, 61]. Compositions of the precipitated compounds and of their corresponding mother solutions are given in Table 4. 

Table 6 summarizes the main compounds that can be prepared by adding alkali metal fluorides to fluorine solutions that contain niobium or tantalum. 

Bizot obtained compounds of MNbF6, M2NbF7 and M3NbF8 type (M = Li, Na, K [77] and M = Rb and Cs [78]) by the direct interaction between NbF5 and alkali metal fluorides. 

In mixtures containing excessive amounts of alkali metal carbonates (molar ratios of M2C03 Nb02F equal to 4 1, 3 1 and 2 1), orthoniobate or a mixture of ortho- and metaniobate and alkali metal fluorides were found. A subsequent increase in the Nb02F concentration in the initial mixture leads to the... 

Interaction between niobium oxide and fluorides, chlorides or carbonates of alkali metals in an ammonium hydrofluoride melt, yielded monooxyfluoroniobates with different compositions, MxNbOF3+x, where they were subsequently investigated [123-127]. According to DTA patterns of the Nb205 - 6NFL HF2 - 2MF system, (Fig. 18) a rich variety of endothermic effects result from the formation of ammonium monooxyfluoroniobate, its thermal decomposition and its interaction with alkali metal fluorides. The number of effects decreases and separation of ammonium ceases at lower temperatures and when going from lithium to cesium in the sequence of alkali metal fluorides. 

Three conceptual steps can be discerned in the definition of the ionic structure of fluoride melts containing tantalum or niobium. Based on the very first thermodynamic calculations and melting diagram analysis, it was initially believed that the coordination numbers of tantalum and niobium, in a molten system containing alkali metal fluorides, increase up to 8. 

The reaction with 4-nitrophenol and pentafluorophenol in the presence of KF-18-crown-6 has been investigated. Pentafluorophenoxide anion was found to be a better leaving group [82JFC(20)439]. Alkali metal fluorides on graphite can act as catalysts for nucleophilic substitution of pentafluor-opyridine [90JFC(46)57]. 

The ternary fluorides M2HgF4 (M = Rb, Cs), obtained by heating the alkali-metal fluorides MF with Hg2F2 under carefully controlled conditions, crystallize in the well-known K2NiF4 type, with octahedra sharing four corners to form layers lDC2[I IgF2F4/2]2 and the cations M+ embedded between these layers.350... 

Calcium disilicide ignites in close contact with alkali metal fluorides, forming silicon tetrafluoride. 

Enantioselective allylations of a-nitro ketones and a-nitro esters with allyl acetates are carried out in the presence of 2 equiv of alkali metal fluorides (KF, RbF, CsF) and 1 mol% palladium catalysts prepared in situ from Pd2(dba)3-CHC13 and chiral phosphine ligands. Moderate enantio-selectivity (ca 50% ee) is reported for allylation of cx-nitroketones (Eq. 5.60). The highest selectivity (80% ee) is observed for allylation of the reaction of tert-butyl ester (Eq. 5.61).93... 

Te(OH) forms adducts with alkali-metal fluorides such as Te(OH) -NaF or Te(OH)8-2KF (102). Single-crystal X-ray diffraction shows that, contrary to the earlier assumption, there is no direct bonding of fluorine to tellurium. The fluoride ions are incorporated into the structure by short O—H F hydrogen bonds (6, 7). 

The reaction of CClaSCl with an alkali metal fluoride (NaF) in a high-boiling polar solvent, e.g., tetramethylenesulfone or acetonitrile, leads in good yield to the important trifluoromethanesulfenyl chloride, CFgSCl (U8,159) ... 

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 primary step in this reaction scheme—the addition of alkali metal fluorides to C=0 double bonds—was flrst observed with per-fluorocarbonyl fluorides and hexafluoroacetone (232). 

When no catalyst is used or if KF and NaF are present as catalysts, CIF is the main by-product. When the more basic alkali metal fluorides, RbF and CsF, are used, CIF3 is the favored coproduct. The formation of CIF 3 rather than CIF is presumably associated with the more ready formation of C1F2 intermediates with RbF and CsF. Yields of CIF3O from CljO are rather variable and may be affected by the particular alkali fluoride present. Yields of over 40% have been consistently obtained and have reached over 80% using either NaF or CsF. Since NaF does not form an adduct with CIF3O (64), stabilization of the product by complex formation does not seem to influence the CIF3O yields strongly. 

When an alkali metal fluoride or ammonium fluoride is added to a solution of lead tetrafluoride in concentrated hydrofluoric acid, salts of fluoplumbic acid are obtained ... 

Titanium metal also can be produced by electrolytic methods. In electrolysis, fused mixtures of titanium tetrachloride or lower chlorides with alkaline earth metal chlorides are electrolyzed to produce metal. Also, pure titanium can be prepared from electrolysis of titanium dioxide in a fused bath of calcium-, magnesium- or alkali metal fluorides. Other alkali or alkaline metal salts can be substituted for halides in these fused baths. Other titanium com-pouds that have been employed successfully in electrolytic titanium production include sodium fluotitanate and potassium fluotitanate. 

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