Fluorination by sulfur tetrafluoride

In 5o -fluoro-6,17-dioxo steroids and 5a-fluoro-6,20-dioxo steroids the 6-oxo group is preferentially fluorinated by sulfur tetrafluoride. For example, treatment of 3/ -acetoxy-5a-fluoropreg-... 

In trifluorooxopropanoic esters, however, the carbonyl function of the ester group is fluorinated by sulfur tetrafluoride, instead of the 0x0 group.In oxocarboxylic acids, both the 0x0 and acid functions react with sulfur tetrafluoride. 

L Reductions by Metal Alkoxyaluminum Hydrides Jaroslav Malek 2. Fluorination by Sulfur Tetrafluoride Chia-Lin J. Wang... 

Furandicarboxylic acid fluorination by sulfur tetrafluoride in the presence of hydrogen fluoride leads to a mixture of products," " but decarboxylation of 27 in the presence of copper powder in quinoline gives 2-trifluoromethylfuran. 

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 difference between equatorial and axial positions determines the arrangement of bonding pairs and lone pairs around an atom with a steric number of 5. An example is provided by sulfur tetrafluoride, a colorless gas that has industrial uses as a potent fluorinating agent. The Lewis structure of SFq shows four S—F bonds and one lone pair of electrons on the sulfur atom. These five pairs of electrons are distributed in a trigonal bipyramid around the sulfur atom. 

The results so far suggest that stabilization of the intermediate carbocation by an adjacent heteroatom, aromatic ring or by steric factors stimulates fluorination of a CLH bond by sulfur tetrafluoride. 

Oxygen functionalities bonded to a metalloid are replaced by fluorine when reacted with sulfur tetrafluoride. Triphenylphosphane oxide, phenylarsenic acid,219 and triphcnylantimony oxide and its bis(trifluoroacetoxy) derivative222 can be converted by sulfur tetrafluoride into the corresponding organophosphorus, organoarsenic and organoantimony fluorides 16,20 and 21. 

The most useful fluorinations that can be brought about with it are the same as those brought about by sulfur tetrafluoride and diethylaminosulfur trifluoride.19 20 Examples are the formation of 1 and 2,9 3,21 4,22 5,9,23 and 69 24 (note that only the carbonyl reaction requires the presence of a Lewis acid). 

The hydroxy group in a-hydroxy ketones and a-hydroxy esters can be replaced by fluorine using sulfur tetrafluoride. fo obtain good yields of the fluoro esters or fluoro ketones, the reaction conditions must be carefully controlled. In the case of a-hydro.xy ketones 1. diethyl ether is the solvent of choice for the reaction. Without a solvent, fluorination of the carbonyl group atid other side reactions cannot be avoided. ... 

The hydroxy group of hydroxyamino acids and hydroxyamines can be substituted by fluorine with sulfur tetrafluoride under mild conditions if hydrogen fluoride is used as solvent.28 31 fable 2 gives some selected examples for the synthesis of fluoro-substituted amino acids and amines. 

Alcoholic hydroxy groups in hydroxyamincs or hydroxyamino acids are replaced by fluorine with sulfur tetrafluoride in anhydrous hydrogen fluoride. The mechanism of this reaction involves simultaneous S>,1 and SN2 pathways30. 

Perfluoroalkylfuran Derivatives Fluorination of 2,4-furandicarboxylic acid by sulfur tetrafluoride results in the mixture of products 45-47." The carboxylic group in position 4 is more reactive than in position 2 and the yield of the compound 46 higher than that of the compound 47. Decarboxylation of the acid 46 in the presence of copper powder in quinoline gives 3-trifluoromethylfuran. 

Lyalin VV, Grigorash RV, Alekseeva LA, Yagupolskii LM (1975) Fluorination of furantetra-carboxyUc acid by sulfur tetrafluoride. Russ J Oig Chem 11 456-457 (Zh Org Khim 11 460-461)... 

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. 

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. 

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). 

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)... 

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). 

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 ... 

We discovered another synthetic technique that involves the conversion by direct fluorination of hydrocarbon polyesters to perfluoropolyesters followed by treatment with sulfur tetrafluoride to produce new perfluoropolyethers.42 The first paper in this area ofreasearch reported that conversion of poly(2,2-dimethyl-1,3-propylene succinate) and poly( 1,4-butylene adipate) by using the direct fluorination to produce novel branched and linear perfluoropolyethers, respectively. The structures are shown in Figure 14.6. The second paper concerns the application of the direct fluorination technology base directed toward oligomers, diacids, diesters, and surfactants.43... 

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