Fluorine hydrogen exchange

Until recently, halogen substituted alkanes were thought to be inert to xenon difluoride, but detailed examination has shown that common solvents such as dichloromethane (3) and chloroform (4) undergo fluorine-chlorine and fluorine-hydrogen exchange at room temperature due to hydrogen fluoride catalysis.15... 

In the 7-fluoro-l-phenylbicyclo[4.1.0]heptane system 12 (R = Ph R = H X = F = H) the cyclopropyl bond between the bridgehead atoms was cleaved upon hydrogenolysis. The fluorine-hydrogen exchange only took place if the halogen had an endo orientation. An additional methyl group in position 2 renders the Cl — C7 bond susceptible to cleavage. With the fluoro substituent in the exo position the fluoromethylcyclohexane derivative 13 was formed exclusively. ... 

The palladium-catalyzed hydrogenolysis of 2-butoxy-l,l-difluorocyclopropanes 3 resulted in the reductive cleavage of the cyclopropyl bond opposite to the electron-deficient carbon atom. Fluorine-hydrogen exchange in the product was observed as a side reaction. 

The effect of fluorination on the reactivity of carbanions has been reviewed.65 66 Fluorination has the same influences on carbanion stability as does the effect of fluorination on acidity (see Section 1.2.). A lot of information has been derived from the effect of fluorination on CH acidity.43 The effect of fluorination on deuterium-hydrogen exchange processes in the case of highly fluorinated substances has been examined with estimates of pKa for highly fluorinaled substrates.67... 

Hydrogen fluoride can displace chlorines on either side chain or nucleus (especially 2-chloro), and antimony fluoride is specific for all chlorinated methyl groups. Sodium fluoride initially replaces a 4-chloro group (82JFC495). Some of these processes have been subjected to kinetic investigation, which demonstrated that in polar, aprotic solvents fluorine-chlorine exchange is a pseudo first-order, consecutive reaction (87JFC373). 

BTF is prepared industrially from toluene in two synthetic steps 1) free radical perchlorination of the methyl group, followed by 2) fluorine/chlorine exchange of the three chlorine atoms with anhydrous hydrogen fluoride (Scheme 1). The chlorination step may be catalyzed by light of suitable wavelength (UV) and is conveniently carried out in the liquid phase. The fluoride/chloride exchange can be catalyzed by the presence of metal halide compounds, such as pentahalide (Cl, F) salts of antimony and molybdenum, and is effected under a variety of... 

Tennakone et al. reported simultaneous reductive and oxidative photo-catalytic N2 fixation in aerated water in the presence of Nafion films loaded with hydrous iron(III) oxide [84]. (We note that Nafion film is a per-fluorinated ion-exchange membrane that, in the hydrogen-ion form, is a superacid. Some Nafion films are reinforced with Teflon.) Nafion film [85,86] was refluxed in concentrated HC1, washed repeatedly, and boiled in distilled water. The film was immersed in aqueous 0.1 MFeCl3 for 30 min, rinsed with water, and immersed in 0.8 M NaOH for 45 min. The treated film was found to contain particles of hydrous iron(HI) oxide with a diameter of about 48 A. The density distribution of Fe3+ in the treated film was approximately 2/imolcm"2. 

Halogen exchange with KF is not successful ia acetic acid (10). Hydrogen bonding of the acid hydrogen with the fluoride ion was postulated to cause acetate substitution for the haUde however, the products of dissolved KF ia acetic acid are potassium acetate and potassium bifluoride (11). Thus KF acts as a base rather than as a fluorinating agent ia acetic acid. 

A new development features exchange fluorination of 2-chloropyridine with hydrogen fluoride—y-coUidine at 150—200°C to give 94% yield of product (381). 

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. 

Beyer synthesis, 2, 474 electrolytic oxidation, 2, 325 7r-electron density calculations, 2, 316 1-electron reduction, 2, 282, 283 electrophilic halogenation, 2, 49 electrophilic substitution, 2, 49 Emmert reaction, 2, 276 food preservative, 1,411 free radical acylation, 2, 298 free radical alkylation, 2, 45, 295 free radical amidation, 2, 299 free radical arylation, 2, 295 Friedel-Crafts reactions, 2, 208 Friedlander synthesis, 2, 70, 443 fluorination, 2, 199 halogenation, 2, 40 hydrogenation, 2, 45, 284-285, 327 hydrogen-deuterium exchange, 2, 196, 286 hydroxylation, 2, 325 iodination, 2, 202, 320 ionization constants, 2, 172 IR spectra, 2, 18 lithiation, 2, 267... 

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