Cesium fluoride

Carbonyl fluoride, COF2, and oxygen difluoride react in the presence of cesium fluoride catalyst to give bis(trifluorylmethyl)trioxide [1718-18-9] CF OOOCF (31). CF OOF has been isolated from the reaction in the presence of excess OF2 (32). 

An alternative hexafluorobenzene process features exchange fluorination (KF) of hexachlorobenzene in the presence of polar solvents (226,249) or under solvent-free conditions (450—540°C, autoclave) (250). Intermediates such as chloropentafluorobenzene can be further fluorinated to hexafluorobenzene (42—51% yield) by cesium fluoride in sulfolane (226,249). 

No tniodoarsorane has been reported. Triduorodiphenylarsorane [2357-18-8] C22H2QASF2, has been prepared by several methods. One method involves the reaction of benzene with arsenic pentafluoride and subsequent treatment of the resulting salt with cesium fluoride (147) ... 

Cesium perchlorate [13454-84-7], CsClO, mol wt 232.35 and theoretical cesium content hi.25/q, is a crystalline powder that decomposes at 250°C Cesium fluoride [13400-13-0], CsF, mol wt 151.90, theoretical cesium content 87.49%, has a melting point of 682—703°C and a boiling point of 1253°C. Cesium fluoride is an extremely hygroscopic, colorless, crystalline soUd it has a solubUity of 3.665 kg/L of water at 18°C. Cesium fluoride is made by exactly neutrali2ing cesium hydroxide with hydrofluoric acid and evaporating the resultant solution to dryness at 400°C. Excess HE results in a bifluoride salt that does not decompose at 400°C, and carbonate in the starting material gives an alkaline product. 

The cesium ion is more toxic than the sodium ion but less toxic than the potassium, lithium, or mbidium ion. No TLV is stated for cesium or cesium chloride the TLV for cesium hydroxide is 2 mg/m. The oral LD q of cesium chloride for mice is 2300 mg/kg, and for cesium fluoride is 400—700 mg/kg (39). 

Cesium fluoride [13400-13-0] M 151.9, m 703°. Crystd from aqueous soln by adding ethanol. 

Carbon-nitrogen multiple bonds in fluorinated imines and nitriles react with halogen fluoride reagents Imines provide 7V-chloroamine.s on reaction with chlo rme fluoride [62, 121, 122, 123] (equations 23 and 24) or with cesium fluoride and chlorine [124] and A -bromoammes on reaction with cesium fluoride and bromine (equation 24)... 

An allylic pertluonnated carbamon can be generated from tetrakis(trifluo-romethyl)allene and cesium fluoride and can be trapped by reactive alkylating agents 247] (equation 51)... 

Fluoroncytrifluoromethane is prepared in a process that uses cesium fluoride as a catalyst for the reaction between fluorine and carbon monoxide [/ij (equation 1) Bisfluoroxydifluoromethane is prepared in a similar manner from carbon dioxide [id], Fluoroxymethane was prepared recently [14]... 

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... 

A one-pot conversion of benzyl alcohols to benzyl fluorides by treatment of the alcohols with a combination of methanesulfonyl fluoride, cesium fluoride and 18-crown 6 ether in tetrahydrofuran has been repotted The reaction involves mesylation of the alcohols followed by cleavage of the resultant mesyl esters with a fluoride ion The reaction has been extended also to certain heterocycles bearing the N hydroxymethyl group [43] (equation 31)... 

Fluorination of trifluoromethanesulfonyl carbohydrates with cesium fluoride under forcing conditions (130 °C in dimethylformamide) [55] or the use of acetyl protected substrates [56] gives considerably lower yields... 

A variety of media have been used for the Wallach fluorination reaction anhydrous hydrogen fluoride alone or with cosolvents such as methylene chloride, benzene, or tetrahydrofuran and hydrogen fluoride-pyridine alone or with co solvents such as benzene, glyme, or acetic acid [42,43, 46 50] Solutions of cesium fluoride, tetraethylammonium fluoride, or tetrabutylammonium fluoride in strong acids such as methanesulfonic acid or trifiuoroacetic acid with numerous cosolvents have also been studied [48, 49]... 

The nucleophilic displacement of halogens by pentafluorophenoxide ion resulted in the formation of the corresponding esters [31] (equation 29) (Table 12). Reactions of trifluoromethanesulfinyl fluoride with fluoro alcohols in the presence of sodium fluoride or cesium fluoride are used to prepare sulfmates [32] (equation 30) (Table 12). 

Perfluoroisobutylene and potassium sulfide give 2,4-bis[hexafluoroisopro-pylidene]-l,3-dithietane and a small amount of the bis(perfluoro-tcrr-butyl)trisul-fide. The trisulfide is the result of a reaction of the nascent perfluoro-rerr-butyl carbanion with sulfur. The same products in different yields are obtained with sulfur and cesium fluoride [i] (equation 2). 

Tetrafluoroethylene gives highly branched, internally unsaturated alkenes on contact with cesium fluoride in aprotic solvents [23, 24] (equation 18)... 

Cesium fluoride-promoted telomenzation of equimolar amounts of perfluoro 2-butyne and 2-bromoperfluoro-2-butene gives a mixture of hexadienes or, with... 

Among the many methods of generating difluorocarbene, the treatment of bromodifluoromethylphosphonium bromides with potassium or cesium fluoride is particularly useful at room temperature or below [II, 12 13] The sodium iodide promoted decomposition of phenyl(trifluoromethyl)mercury is very effective at moderate temperatures [S, 14] Hexafluoropropylene oxide [/5] and chlorodifluo-roacetate salts [7] are excellent higher temperature sources of difluorocarbene... 

Frequently, the decomposition of fluorine compounds results in a product with fewer carbon atoms through loss of carbon monoxide, carbon dioxide, or even an organic molecule Perfluonnated a-diketones undergo decarbonylanon with cesium fluoride in diglyme [90] (equation 57)... 

Isomerization of fluoroolefins by a shift of a double bond is catalyzed by halide 10ns [7] The presence of crown ether makes this reaction more efficient [74] Prolonged reaction time favors the rearranged product with an internal double bond (equations 3-5) Isomerization of perfluoro-l-pentene with cesium fluoride yields perfluoro-2-pentenes in a Z ratio of 1 6 [75] Antimony pentafluoride also causes isomenzation of olefins leading to more substituted products [76]... 

Dibromotetrafluoropropene passed over copper yields tetrafluoroallene (39%) and perfluoropropyne (11%) [23] Similarly, perfluorocyclobutene in a nickel flow reactor in contact with cesium fluoride at temperatures over 450 °C yields perfluorobutyne (40%) [24] At 590-600 °C, the yield is greater than 90% [25]... 

Nucleophilic halogen exchange, using cesium fluoride and 18-crown-6 in tetrahydrofuran, gave high yields of 2-, 3-, and 2,3,-di-fluoroquinoxalines from the chloro analogues [87H)26)1215]. The Balz-Schiemann process has been used successfully to make 2-fluoro-quinoxaline (84MI8). 

Most a-chloro enamines can be readily converted into the corresponding a-fluoro enamines by reaction with potassium or cesium fluoride or to the iodo enamines by reaction with potassium iodide. All a-halo enamines are highly hygroscopic and must be stored in sealed tubes. 

More recently, the addition of cyanide ion, generated from TMS cyanide and cesium fluoride, to a-aziridino N-siflfinyl imines, being chiral either at the a position or at sulfur, has been examined [87] (Scheme 28). The configuration of the newly formed stereocenter was determined only by the chiral (S)-sulfinyl group. In fact, the R configuration (diastereomeric excess, de, 98%) was obtained from either the Q -(ii)-imine 186 or the a-(S)-imine 188, giving 187 and 189, respectively. Acyclic 2,3-diaminonitriles can be obtained... 

Sulphines may react as dienophiles with 1,3-dienes with the formation of cyclic sulphoxides. Unstable 2,2-dichloro-5,6-dihydro-2ff-thiin-l-oxide 191 was formed in an exothermic reaction between 173aandcyclopentadieneat — 40 (equation 101). The simplest, parent sulphine, CH2 = S = O, prepared in situ by treatment of a-trimethylsilylmethanesulphinyl chloride with cesium fluoride, reacts with cyclopentadiene to give bicyclic, unsaturated sulphoxide 192 as a mixture of two diastereoisomers in a 9 1 ratio (equation 102). On the other hand, a,j8-unsaturated sulphine 193 (generated by thermolysis of 2-benzylidene-l-thiotetralone dimer S-oxide) in boiling toluene behaves as a 1,3-diene and was trapped by norborene forming sulphoxide 194 in 78% yield ° (equation 103). 

Especially for large-scale work, esters may be more safely and efficiently prepared by reaction of carboxylate salts with alkyl halides or tosylates. Carboxylate anions are not very reactive nucleophiles so the best results are obtained in polar aprotic solvents45 or with crown ether catalysts.46 The reactivity order for carboxylate salts is Na+ < K+ < Rb+ < Cs+. Cesium carboxylates are especially useful in polar aprotic solvents. The enhanced reactivity of the cesium salts is due to both high solubility and minimal ion pairing with the anion 47 Acetone is a good solvent for reaction of carboxylate anions with alkyl iodides48 Cesium fluoride in DMF is another useful... 

In contrast, perfluoromethylenecyclopropane (105) failed to give any thermal dimerization (cesium fluoride promotes its dimerization, but not in a [2 + 2] fashion) [29], while tetrafluoroethylene and other 1,1-difluoroalkenes readily undergo thermal [2 + 2] dimerization [123]. 

Fluoride ion is effective in promoting the reduction of aldehydes by organosil-icon hydrides (Eq. 161). The source of fluoride ion is important to the efficiency of reduction. Triethylsilane reduces benzaldehyde to triethylbenzyloxysilane in 36% yield within 10-12 hours in anhydrous acetonitrile solvent at room temperature when tetraethylammonium fluoride (TEAF) is used as the fluoride ion source and in 96% yield when cesium fluoride is used.83 The carbonyl functions of both p-anisaldehyde and cinnamaldehyde are reduced under similar conditions. Potassium bromide or chloride, or tetramethylammonium bromide or chloride are not effective at promoting similar behavior under these reaction conditions.83 Moderate yields of alcohols are obtained by the KF-catalyzed PMHS, (EtO SiH, or Me(EtO)2SiH reduction of aldehydes.80,83,79... 

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... 

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