Fluorination with metal fluorides

High-valency metal fluoride fluorination of pyridine [82JFC(21)171], quinoline [82JFC(21)413], and 2-methylfurans [91 JFC(51)179] has been reported. With 2-methylfuran a complex mixture of stereoisomers of partially fluorinated oxolans was obtained. These can be dehydrofluorinated to fluorooxolens and no furans have been observed. Conformation and structural group were found to influence the direction and readiness toward dehydrofluorination [91 JFC(52) 165]. 

Further, the metal fluorides SbFs (with admixture of small quantities of SbCls), HgF2, and AgF are also found suitable for the fluorination of sulfenyl halides, e.g.. 

Nucleophilic substitution in fluorinated compounds can also be achieved in the presence of metal fluorides, and with complete inversion of configuration, but the yields are at best only moderate (e. g., the synthesis of 13). ... 

Firth, W.C., Jr. Reactions of pentafluoroguanidine and tetrafluoroformamidine with alkali metal fluorides. Fluorine-containing diaziridines. J. Org. Chem. 1968, 33, 3489. 

Figure 4.8 Three possible modes of adsorption for anhydrous HCI at metal fluorides. (Reprinted with permission from M. Nickkho-Amiry and J. M. Winfield, J. Fluorine Chem., 128, 344-352 Copyright (2007) Elsevier Ltd.)...

Arsenic pentafluoride can be prepared by reaction of fluorine and arsenic trifluoride or arsenic from the reaction of NF O and As (16) from the reaction of Ca(FS02)2 and H AsO (17) or by reaction of alkaH metal or alkaline-earth metal fluorides or fluorosulfonates with H AsO or H2ASO2F (18). 

CoF is used for the replacement of hydrogen with fluorine in halocarbons (5) for fluorination of xylylalkanes, used in vapor-phase soldering fluxes (6) formation of dibutyl decalins (7) fluorination of alkynes (8) synthesis of unsaturated or partially fluorinated compounds (9—11) and conversion of aromatic compounds to perfluorocycHc compounds (see Fluorine compounds, organic). CoF rarely causes polymerization of hydrocarbons. CoF is also used for the conversion of metal oxides to higher valency metal fluorides, eg, in the assay of uranium ore (12). It is also used in the manufacture of nitrogen fluoride, NF, from ammonia (13). 

Replacement of Hydrogen. Three methods of substitution of a hydrogen atom by fluorine are (/) reaction of a G—H bond with elemental fluorine (direct fluorination, (2) reaction of a G—H bond with a high valence state metal fluoride like Agp2 or GoF, and (J) electrochemical fluorination in which the reaction occurs at the anode of a cell containing a source of fluoride, usually HF. 

At 225—275°C, bromination of the vapor yields bromochloromethanes CCl Br, CCl2Br2, and CClBr. Chloroform reacts with aluminum bromide to form bromoform, CHBr. Chloroform cannot be direcdy fluorinated with elementary flourine fluoroform, CHF, is produced from chloroform by reaction with hydrogen fluoride in the presence of a metallic fluoride catalyst (8). It is also a coproduct of monochlorodifluoromethane from the HF—CHCl reaction over antimony chlorofluoride. Iodine gives a characteristic purple solution in chloroform but does not react even at the boiling point. Iodoform, CHI, may be produced from chloroform by reaction with ethyl iodide in the presence of aluminum chloride however, this is not the route normally used for its preparation. 

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

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],... 

Metal halides can in some cases, be used to replace other atoms or groups besides fluorine with halogen Polyfluoroacyl fluorides and chlorides can be converted to fluoroalkyl iodides by simply heating the reactant in the presence of an alkali metal iodide [[Pg.382]

The alkoxide formed by attack of the carbonyl group of perfluorobutyrolactone opens the oxirane ring of hexafluoropropene oxide at the central carbon atom [37] (equation 33). A fluorinated sultone reacts with halogenoalkanes in the presence of metal fluoride [3S] (equation 34). 

Fluorine is the most reactive of all elements, in part because of the weakness of the F—F bond (B.E. F—F = 153 kj/mol), but mostly because it is such a powerful oxidizing agent (E ed = +2.889 V). Fluorine combines with every element in the periodic table except He and Ne. With a few metals, it forms a surface film of metal fluoride, which adheres tightly enough to prevent further reaction. This is the case with nickel, where the product is NiF2. Fluorine gas is ordinarily stored in containers made of a nickel alloy, such as stainless steel (Fe, Cr, Ni) or Monel (Ni, Cu). Fluorine also reacts with many compounds including water, which is oxidized to a mixture of 02> 03> H202, and OF2. 

TaF5 and NbF5 are prepared from their respective oxides by fluorination with fluorine, F2, or with anhydrous hydrogen fluoride, HF [73-75]. Rakov et al. reported the interaction between niobium metal and anhydrous hydrogen fluoride as being the most effective way of preparing NbF5 [76]. 

An attempt is also being made to preserve metal-metal bonds during direct fluorination. It has been found that the reaction of fluorine with hexamethyldigermane leads primarily to tris(trisfluoromethyl)-germanium fluoride (34). 

In the fifth paper of this chapter on cathodes, an investigation of thin-film oxide-hydroxide electrodes containing Cr, Ni, and Co compounds was authored by N. Vlasenko et al. The thin-films were produced by electrochemical deposition from transition metal aqueous fluorine-containing electrolytes onto steel substrates. These thin-films were tested in Li coin cells. Electrochemical activity appears to scale with the amount of fluoride used in the deposition the larger concentration of fluoride in the bath, the greater the capacity. One Ni oxide-hydroxide film electrode showed greater than 175 mAh/g reversible capacity on the 50th cycle with excellent coulombic efficiency. 

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