Cesium/potassium fluoride

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... 

The effectiveness of various sources of fluoride ion in the displacement of the trifluoromethanesulfonic group has been demonstrated while introducing a fluorine atom into the five-membered carbocyclic ring of a prostaglandin precursor Treat tnent of the corresponding triflyl derivative with potassium fluoride in acetonitrile or with cesium fluonde in refluxing diinethylformamide or hexamethylphosphoric... 

Rearrangement of fluorine with concomitant ring opening takes place in fluorinated epoxides Hexafluoroacetone can be prepared easily from perfluo-ropropylene oxide by isomerization with a fluorinated catalyst like alumina pre treated with hydrogen fluoride [26, 27, 28] In ring-opening reactions of epoxides, the distribution of products, ketone versus acyl fluoride, depends on the catalyst [29] (equation 7) When cesium, potassium, or silver fluoride are used as catalysts, dimenc products also are formed [29]... 

Diphenylsilane reacts with two equivalents of neat n-heptanal in the presence of anhydrous cesium fluoride within three minutes at room temperature to form di-n-hep toxy diphenylsilane quantitatively (Eq. 162).319 Potassium fluoride and potassium phthalate are considerably less effective promoters, even at temperatures up to 140°.319... 

The addition of chlorine monofluoridc across the C = 0 bonds in difluorophosgene, per-fluoroacyl fluorides, and perfluoroketones with the formation of hypochlorites occurs only in the presence of the catalysts potassium fluoride, rubidium fluoride, cesium fluoride80,81 or the strong Lewis acids hydrogen fluoride, boron trifluoride, or arsenic(V) fluoride.82 The cesium fluoride catalyzed reactions are carried out in an autoclave for 2-3 hours at — 20"C or left overnight.80... 

Difluorotris(perfluoroalkyl)-25-phosphancs (Rf)3PF2 give stable salts with cesium fluoride, potassium fluoride, sodium fluoride or arenediazonium fluorides, i.e. Cat + [(RF)3PF3] , where Cal+ = Cs +. K+, Na +, ArN2+. The last are difficult to dissolve and they decompose at much lower temperatures (60-90 C) than tetrafluoroborates and hexafluorophosphates. which allows more complete precipitation of diazonium salts from water solutions and their conversion into aryl fluorides 6 without tar formation.6... 

In spite of the fact that cesium fluoride is very expensive and needs care in handling (very hygroscopic ), it is the reagent of choice for several reactions where halogens and fluorosulfonate groups have to be replaced by fluorine in aromatic and heterocyclic compounds. Cesium fluoride is more reactive than potassium fluoride and also possesses greater solubility. Often a phase-transfer catalyst is added to aid and enhance the reaction rate and yield of the products. 

This method has been extended to heterocycles bearing a hydroxymethyl-substituted nitrogen. Thus, ethyl l-(hydroxymethyl)pyrazole-4-carboxylate (10) is converted into ethyl 1-(fluoromethyl)pyrazole-4-carboxylate (11) in 76% yield with cesium fluoride/methanesulfonyl fluoride/18-crown-6 system.167 Potassium fluoride did not react at all and tetrabutylammonium fluoride leads to decomposition and formation of coupling products. 

A detailed study of the rearrangement of heptafluoro-2-phenylbut-1-ene (11) to but-2-ene 12 and the E,7. equilibration of 12 showed that lithium and sodium fluorides do not catalyze the rearrangement. Cesium, rubidium, and potassium fluorides are effective catalysts, in that order of decreasing reactivity.25... 

Perfluoro(l-methylcyclopentene) (10) can be prepared from perfluoro(methylenecyclopen-tane) in 98 % yield with cesium fluoride and in 94% yield with potassium fluoride in diglyme.31... 

Perfluoro(l,2-dimethylenecyclobutane) (17) isomerizes in 98% yield to perfluoro(2-methyl-3-methylenecyclobutcnc) (18) by heating at 100 C with cesium fluoride for 1 hour. No reaction was observed with potassium fluoride, cesium chloride, potassium chloride, or lithium bromide.48... 

An efficient synthesis of hexafluorobut-2-yne25,26 combined the knowledge that hexafluorocy-clobutene thermally rearranges to hexafluorobuta-1,3-diene (vide supra) and that cesium or potassium fluoride isomerize dienes to alkynes (see Section 5.1.2.3.). Thus, when hexafluoro-cyclobutene is passed over cesium or potassium fluoride at 590-600 C, hexafluorobut-2-yne is obtained in yields up to 90%, with 95% recovery of material. 

Cesium fluoride-Tetraalkoxysilanes, 69 Hexamethylphosphoric triamide, 142 Methyl acrylate, 183 a-Methylbenzylamine, 185 Methyl vinyl ketone, 193 Potassium t-butoxide, 252 Potassium f-butoxide-Xonotlite, 254 Potassium fluoride-Alumina, 254 Tin(II) trifluoromethanesulfonate, 301 Titanium(IV) chloride, 304 Trityl perchlorate, 339 Vinyl(triphenyl)phosphonium bromide, 343... 

Cesium fluoride-Calcium fluoride, 256 Potassium fluoride-Calcium fluoride, 256... 

IONIC CRYSTAL. A crystal ihut consists effectively of ions bound lugclher by Iheir electrostatic attraction. Examples of such crystals are the alkali halides, including potassium fluoride, potassium chloride, potassium bromide, potassium iodide, sodium fluoride, and the other combinations of sodium, cesium, rubidium or lithium ions with fluoride, chloride, bromide or iodide ions. Many other types of ionic crystals are known,... 

However, of all the salts tested (RbCl, CsF, CS2CO3 0.2 mol per 1 mol KOH), only cesium fluoride shows a perceptible catalytic effect (yield gain up to 8%) at the stage of pyrrole formation for only the first three hours (Fig. 2, curve 3). The observed effect can be explained in terms of poor solubility of potassium fluoride in DMSO (86MI1). 

The ratio between 81 and 82 depends on the alkaline metal fluoride used. Thus if cesium fluoride is employed, the product is 81 alone, whereas in the case of potassium fluoride, 81 and 82 are formed, the ratio between these compounds depending on the nature of substituent in the benzene ring C6H5X for KF, 20 °C, MeCN (the values in parentheses are yields of 81 and... 

For this reason, electrophilic additions such as addition of hydrogen halides are very difficult, as can be seen in Explanations 13, 14, and 15. But because of the low overall electron density, the double bonds in perfluoroalkenes are easily attacked by nucleophiles such as fluoride ion. If perfluoropropene is treated with dry potassium fluoride in a proton-donor solvent such as formamide, the fluoride anion joins the less negative carbon of the double bond and forms a negatively charged intermediate that readily reacts with the proton of formamide to give 2 H-perfluo-ropropane [5/]. Such a nucleophilic addition takes place with other fluorides such as cesium fluoride, tetraethylammonium fluoride, and sil-... 

Although rubidium and cesium fluoride are more reactive than potassium fluoride, cf. the yields of 2-fluoro-1,4-dinitrobenzene (5), their application is limited by their high cost. A typical procedure with cesium fluoride is given by the formation of 1,8-dilluoroanthraquiiione (6). ... 

Potassium fluoride is the most frequently used metal fluoride for the substitution of inorganic ester groups by fluorine. Cesium fluoride in combination with crown ethers is preferable in difficult cases, while silvcr(l) fluoride is seldom used. 

Rubidium [ F]fiuoride is used as a reagent for the [ F]fluorodenitration of nitroaromatic compounds containing activating groups (e.g., CN, COR, CO2R, OH. OMe, etc.). Rubidium [ F]fluoride gives better yields than other fluoride salts, such as potassium fluoride or cesium fluoride, which are extremely hygroscopic. This method constitutes a very convenient route to [ F]fluorine-labeled aromatics, which are often required in radiopharmaceutical studies. 

Perfluoro(2-methylpropene) reacts with elemental sulfur in the presence of potassium fluoride or cesium fluoride to yield bis[tris(trifluoromethyl)methyl] trisulfide (3). ... 

When activated by anionic catalysts [potassium fluoride, cesium fluoride, tctraalkylammonium fluorides, tris(dimethylamino)sulfonium difluorotrimethylsilicate, phosphazenium, hexa-methylpiperidinium and cobaltoccnium fluorides, tetrabuiylammonium difluoro(triphenyl-silyl)silicatc. the complex tetrakis(dimethylamino)ethene/pcrfluoropropene, ammonium (and phosphonium) periluorocyclobuianc ylides], trimethyl(perfluoroalkyl)silanes will generate C-Rp bonds from carbon-halogen bonds. 

Trimethyl(perfluoroalkyl)silanes react with perfluorinated ketones in the presence of cesium or potassium fluoride in diethyl ether (THF, MeCN), giving perfluorinated tertiary alcohols 13. ... 

Destlylation. Anhydrous cesium fluoride desilylates trimethylsilylmethyl-sulfonium, trimethylsilylmethylammonium, and trimethylsilylmethylphosphonium salts at room temperature to produce ylides, which undergo various useful transformations. Use of potassium fluoride-18-crown-6 or a tetraalkylammonium fluoride gives products in low yield in these reactions. The trimethylsilylmethyl-onium salts are prepared by alkylation of sulfides, amines, imines, and phosphines with (trifluoromethanesulfonylmethyl)trimethylsilane (1). 

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