Sulfur tetrafluoride fluorination

Results of the sulfur tetrafluoride fluorination of benzenecarboxylic acids strongly depend on the nature of a benzene ring substituent Benzoic, toluic, and particularly p-methoxybenzoic acids give poor yields of the respective benzotri-... 

C21-0008. Sulfur tetrafluoride fluorinates boron trichloride according to the following unbalanced equation BCI3 + SF4 BF3 + SCI2 + CI2 This is both a redox reaction and a metathesis reaction, (a)... 

The sulfur tetrafluoride fluorination of most nonhalogenated quinones and hydroxyquinones is erratic in behavior and generally occurs with isomerization, substitution of a hydrogen atom by fluorine, and addition of fluorine to the carbon atom / to the carbonyl group. Thus, the fluorination of benzo-l,4-quinone results in aromatization to give 1,2,4-trifluorobenzene (8) as the sole product.41... 

Sulfur tetrafluoride fluorination of the methyl group has been reported.253 Thus, the reaction with 2,5-dimethylfuran-3,4-dicarboxylic acid gives, besides the expected acid fluoride 16 and 2,5-dimethyl-3,4-bis(trifluoromethyl)furan (17a), higher fluorinated compounds, 2-(difluoro-methyl)-5-methyl-3,4-bis(trifluoromethyl)furan (17b) and 2-methyl-3,4,5-tris(trifluoromethyl)-furan (17c). Low yields are due to considerable tar formation. 

Steric approach control, 67 Steric strains, 71 Steric strain control, 69 Steroid hydrogenation, 111 5/3-Stigmast-22-en-3-one, 130 Stigmasterol, 266 Sulfur dichloride, 459 Sulfur tetrafluoride, 459, 472 Sulfur tetrafluoride fluorination, 471 Surface catalysts, 157... 

Sulfur tetrafluoride fluorination of aryl perfluoroalkyl esters provides a route to stable aryl perfluoroalkyl ether compounds (1). By using nitrophenyl esters of perfluoroalkyl-ene and perfluoroalkylene ether dicarboxylic acids, a, w-bis (m-nitrophenoxy) perfluoroalkylene ether intermediates were prepared. The conversion of these products to the corresponding amino and isocyanatophenoxy derivatives is described. Reaction of the diamines with benzophenone-tetracarboxylic dianhydride resulted in formation of poly-imides. Cyclotrimerization of the diisocyanate intermediates formed polyisocyanurates. Both the imide and iso-cyanurate polymers have high thermal, oxidative, and hydrolytic stability. 

We also developed a number of other useful new fluorinating reagents. They ineluded a convenient in situ form of sulfur tetrafluoride in pyridinium polyhydrogen fluoride, selenium tetrafluoride, and ey-anurie fluoride. We introdueed uranium hexafluoride (UFg), depleted from the U-235 isotope, which is an abundant by-product of enrichment plants, as an effective fluorinating agent. 

Nonmeta.ls, Sulfur reacts with fluorine to yield the remarkably stable sulfur hexafluoride, SF. Operating conditions must be controlled because a mixture of the lower fluorides such as disulfur difluoride [13709-35-8] 2 2 disulfur decafluoride [5714-22-7] 2 10 sulfur tetrafluoride [7783-60-0] SF4, may also be formed. When this reaction is carried out between 310 and 340°C, SF is primarily obtained and essentially no SF and only trace amounts of lower fluorides. Below 300°C, and preferably at ca 275°C, SF is the primary product. At 450—500°C, a mixture comprising ca 50% SF and the lower sulfur fluorides is formed (see Fluorine compounds, inorganic-sulfur). 

With alcohols, mixtures of alkyl fluorides and alkyl ethers are obtained (100). Alcohols beating electron-withdrawiag groups can be converted to the corresponding fluorides ia high yield (101). Sulfur tetrafluoride replaces the carboayl oxygea with fluorine (100,102). 

Preparation. In the laboratory, sulfur tetrafluoride is made by combining SCI2 and NaF suspended in acetonitrile at ca 77°C (106). For commercial production, SF is made by direct combination of sulfur with elemental fluorine (107). Commercial appHcations of SF are limited. It is available from Air Products and Chemicals. 

Disulfur decafluoride does not react rapidly with water, mercury, copper, or platinum at ambient temperatures. There is evidence that it slowly decomposes on various surfaces in the presence of water when stored in the vapor state (118). It is decomposed by molten KOH to give a mixture of potassium compounds of sulfur and fluorine. The gas reacts vigorously with many other metals and siUca at red heat (114). At ca 156°C it combines with CI2 or Br2 to form SF Cl or SF Br (119,120). At ca 200°C, S2F2Q is almost completely thermally decomposed into the hexa- and tetrafluoride (121). 

Sulfur tetrafluoride [7783-60-0] SF, replaces halogen in haloalkanes, haloalkenes, and aryl chlorides, but is only effective (even at elevated temperatures) in the presence of a Lewis acid catalyst. The reagent is most often used in the replacement of carbonyl oxygen with fluorine (15,16). Aldehydes and ketones react readily, particularly if no alpha-hydrogen atoms are present (eg, benzal fluoride [455-31-2] from benzaldehyde), but acids, esters, acid chlorides, and anhydrides are very sluggish. However, these reactions can be catalyzed by Lewis acids (HP, BF, etc). 

Depending on the ring substituent, trifluoromethoxyben2enes can be made by the sequential chlorination—fluorination of anisole(s) (351—354). A one-step process with commercial potential is the BF (or SbF2)-cataly2ed reaction of phenol with carbon tetrachloride/hydrogen fluoride (355). Aryl trifluoromethyl ethers, which may not be accessible by the above routes,may be made by fluorination of aryl fluoroformates or aryl chlorothioformates with sulfur tetrafluoride (348) or molybdenum hexafluoride (356). 

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. 

The recent discovery of a convenient synthesis of sulfur tetrafluoride from sulfur dichloride and sodium fluoride in acetonitrile invited the application of this reagent in fluorination reactions. Hasek, Smith and Engelhardt showed that carboxylic acids and their derivatives can be converted into trifluoromethyl derivatives and that aldehydes and ketones are converted into 5 em-difluoro compounds. They also observed that the reaction was acid... 

Replacement of ketones with fluorine by reaction with sulfur tetrafluoride-hy-drogen fluoride, 471... 

Perfluorodimethyladamantane is prepared from adamantane dicarboxylic acid by treatment with sulfur tetrafluoride followed by energetic fluorination with cobalt trifluoride over two temperature ranges [S] (equation 15)... 

A nonconventional synthesis of the known inhalation anaesthetic, 2-bromo-2 chloro-l,l,l-trifluoroethane (Halothane), based on the reaction of ethyl 1,2 di bromo-1,2-dicliloroethyl ether with anhydrous hydrogen fluoride and sulfur tetrafluoride, has been patented The reaction presumably involves cleavage of the ether linkage, followed by fluorination of the intermediate bromochloroacetyl halide with sulfur tetrafluoride, ethyl halides are the by-products [2] (equation 2)... 

Reactions of alcohols with sulfur tetrafluoride, because of decomposition and/or polymerization, usually do not give fluorinated products However, in the presence of a hydrogen fluoride scavenger like triethylamine or pyridine, even such sensitive substrates as benzylic alcohols [555], 2-phenylethanol, and 2-furylmethanol [554] can be fluorinated to give the expected fluoro derivatives (equation 73)... 

Highly fluorinated tertiary alcohols usually give olefins on iluormation with sulfur tetrafluoride [759/, but in certain cases, replacement of the hydroxyl group with fluorine occurs under mild conditions Hexafluoro-2-arylpropan-2-ols react with sulfur tetrafluoride at low temperatures to give high yields of heptafluoro-isopropylarenes [766] (equation 77), and similarly, 3,8 dihydroxy 9,9,9,10,10,10-hexafluoro-p-menthane affords 3,8,9,9,9,10,10,10-octafluoromenthane [766] (equation 78)... 

Polyhalodiethyl ethers are also formed in the reaction of sulfur tetrafluoride with perhaloacetaldehydes in the case of chloral, a chlorine-fluorine rearrangement occurs [I7Q] (equations 82 and 83). 

Treatment of a- or P hydroxyacids with sulfur tetrafluoride leads to conver Sion of the carboxylic group into the tiifluoromethyl group, but the hydroxyl group undergoes either fluorination, fluorosulfination, esterification, or dehydration to form esters, ethers, or alkenes The ratio of the products depends on P substitution [209, 210] (equations 103 and 104)... 

Fluorination of tetrachlorophthalic acid hemihydrate with an excess of sulfur tetrafluoride, or of tetrachlorophthalic anhydride with a sulfur tetrafluonde-hydro-gen fluoride reagent, provides an efficient synthesis of 4,5,6,7- tetrachloro-1,1,3,3-tetrafluorol,3-dihydroisobenzofuran. 3,4,5,6-Tetrachloro-2-(trifluoromethyl)-benzoyl fluoride is formed as a by-product [217] (equation 111). 

Furan-2-carboxylic acid reacts with sulfur tetrafluoride at 0 °C to give 2-furoyl fluoride, but attempts at further fluorination results in resin formation [222] A second carboxylic group and/or electron withdrawing substiments, such as the nitro or tnfluoromethyl group, stabilize the furan ring Thus, turandicar-... 

The reaction ot tormamides with sulfur tetrafluoride in the presence of potassium fluoride leads to replacement of both carbonyl oxygen and hydrogen with fluorine. The formyl group is directly converted into the trifluoromethyl group A-(trifluoromethyl)amines are formed in near quantitative yields [233] (equation 121)... 

Results of fluorination of lactones with sulfur tetrafluoride depend on the ring size. y-Butyrolactone undergoes ring cleavage to give y-fluorobutyryl fluoride, which IS further fluormated to 1,1,1,4-tetrafluorobutane. The six-membered 1,4-di-... 

These reactions differ from those of sulfur tetrafluoride with carbonyl compounds in that a formal oxidation-reduction of the sulfur atoms m the thiocarbonyl compound and sulfur tetrafluoride molecule occurs, resulting in the formation of free sulfur and the complete utilization of the fluorine atoms in sulfur tetrafluoride. 

Sulfur tetrafluoride, SF4, though extremely reactive (and valuable) as a selective fluorinating agent, is much more stable than the lower fluorides. It is formed, together with SFg, when a cooled film of sulfur is reacted with F2, but is best prepared by fluorinating SCI2 with NaF in warm acetonitrile solution ... 

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