Fluorine chlorine exchange

Another example of a simultaneous chlorine-fluorine exchange and rearrangement IS the reaction of orr/io-methylphenylchloroformate with hydrogen fluoride to give a stable tetrafluorobenzodioxtn [34] (equation 25)... 

Triethylbenzylammonium chloride and potassium fluoride containing 1% water can provide chlorine-fluorine exchange of activated halides in the absence of a solvent. This mixture also can displace the chlorine of a chlorodifluoromethyl group to form a trifluoromethyl group [62] (equation 36). 

The main product of the reaction was CF2=CHC1. Moreover, two secondary alkenes CFC1=CHC1 (Z and E) were formed from CF2 = CHCl by successive chlorine-fluorine exchanges [10], After a fast initial deactivation, the catalyst stabilized. The catalytic activity for the dehydrofluorination reaction was estimated after a 5 hours reaction from the sum of the amount of alkenes. 

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 introduction of the perfluorohalogenosulfenyl group into aromatic compounds was accomplished long before the preparation of sulfenyl halides. The CFgS-subBtituted compounds have been synthesized largely by chlorination of the side chain in arylmethylthioethers followed by chlorine-fluorine exchange. This method was applied for the first time in the synthesis of trifluoromethylmercaptobenzene 92, 140, 172) ... 

Chlorine fluorine exchange between alkyl- or arylehloroboranes and antimony(Ill) fluoride proceeds very readily with evolution of heat. The compounds listed in Table 2 have been obtained by this reaction. 

Table 2. Chlorine Fluorine Exchange between Alkyl- or Arylchloroboranes and Antimony(III) Fluoride...

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... 

The chlorine —fluorine exchange in l-chloro-2,4-dinitrobenzene has been systematically investigated using potassium fluoride among other reagents in the presence of several crown ethers.93... 

Side chain fluormated aryl isocyanates are an important group of substances used in the manufacture of biologically active compounds The synthetic routes to the meta- and para trifluoromethylphenyl isocyanates permit the chlorine-fluorine exchange with hydrogen fluoride to proceed under moderate conditions and m a virtually quantitative manner (equation 22)... 

Minkwitz et al.604 have prepared the hexafluorometalates of cations 308. The reaction of a,a-dichloromethyl methyl ether in HF-Lewis acid solution at —78°C leads to the formation of chloro cation 308-C1, whereas at -65°C fluoro derivative 308-F is isolated as a result of chlorine-fluorine exchange [Eq. (3.80)]. Interestingly, the chlorine atom and the methyl group are trans in the hexafluoroantimonate salt of cation 308-C1, whereas the fluorine atom and the methyl group are cis in cation 308-F. The arrangement of the C—O—C—H atoms is nearly planar with F/Cl—C—O—C torsion angles of 2.84° (308-F) and 179.0° (308-C1). The C Obond distances (1.224 and 1.479 A for cation 308-F, and 1.252 and 1.517 A for cation 308-C1) reveal dominant oxonium ion character. 

The synthesis of fluotrimazole starts from m-xylene. Peroxide catalyzed perchlorination converts this to m-trichloromethyl-benzo-trichloride. m-Trichloromethyl-benzotrifluoride is then obtained by selective chlorine/fluorine exchange. This key product is also readily accessible on a technical scale by conproportionation of the two corresponding m-trihalomethyl-benzotrihalogenides. Friedel-Crafts reaction with benzene leads to trifluoromethyl-tritylchloride, which reacts smoothly with 1,2,4-triazole in polar solvents to give fluotrimazole. 

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]. 

In the reaction of a-(trihalomcthyl)sulfanyl ketones with hydrogen fluoride,, -difluoroalkyl fluoridothiocarhonates 14 are obtained instead of the expected trifluoromethyl sulfides.The reaction is thought to proceed via an initial chlorine-fluorine exchange reaction followed by rearrangement into the /i-difluorinated product. 

Fluorination of thiophene and derivatives and of 1,4-dithiane [241] with KC0F4 gives a series of fluorinated derivatives. Chlorine-fluorine exchange in sulphides is also possible in some cases [242] (Figure 8.86). 

The synthesis of the fluoro phosphines is accomplished using chlorine-fluorine exchange in the corresponding chloro phosphines with sodium fluoride in sulfolane (tetrahydrothiophene 1,1-dioxide). The preparation of representative fluoro phosphine complexes with both a zero-valent and bivalent transition metal, Mo(0) and Ni(II), respectively, is also described. 

Perfluoroalkoxy groups and, especially, the trifluoromethoxy group, are commonly used as structural elements in pharmaceuticals (Section 4.5) and organic materials (Section 4.4). Aromatic and aliphatic perfluoroalkoxy groups are conveniently accessible via fluorodesulfuration chemistry (see also Section 2.1.5.4). Nevertheless, the technically important trifluoromethoxy arenes, in particular, are produced on a larger scale by a different method, based on chlorine-fluorine exchange with hydrofluoric acid [17] (Scheme 2.172). 

The 1-bromo compound 6b is, untypically for S-bromo derivatives, a relatively stable compound, identified by MS and elemental analysis.26 3,5-Diehloro-l-fluorothiatriazine 6a shows at room temperature dismutation by chlorine/fluorine exchange into 1,3,5-trichlorothiatriazine and 5-chloro-1,3-difluorothiatriazine 7.26... 

It is a gas at room temperature under normal pressures and condenses at +7.1°C (82). The melting point is — 124°C (74)- The isomeric saltlike compound has the structure [PC14][PF6], and may be obtained by careful chlorine-fluorine exchange between [PC14][PC1 ] and AsF3 in AsCU solution (88) ... 

For example, with the sodium salts, chlorine-fluorine exchange takes place (294) according to ... 

Lithium salts differ in behavior from those of potassium, rubidium, and cesium. Thus in the case of lithium fluoride only chlorine-fluorine exchange takes place, whereas potassium, rubidium, and cesium fluorides add onto the alkyl aluminum fluorides and form stable complexes, M[A1R2F2] (294). A similar complex is formed by sodium fluoride, but it breaks down at elevated temperatures (> 200°C) to triethylalane and cryolite (294) ... 

An interesting transformation leading to fiuorinated oxetanes 9 and 10 was reported by Zeifman et al. in 1996. The treatment of (CF3)2C(OH)CCl2CF3 by antimony pentafluoride at low temperature ( 20°C) leads to the formation of oxetanes 9 in 26% yield, while the reaction carried out at elevated temperature (80°C) results in the oxetane 10 formed from 9 as the result of the chlorine-fluorine exchange under action of SbFs. 

In 1991, Krespan reported the preparation of 111 using the sequence, including photochemical chlorination of 1,4-dioxane, chlorine-fluorine exchange, and dechlorination of 1,2-dichlorohexafluoro-1,4-dioxane. ° Compound 114 was prepared using similar procedure. 

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