Sulfur containing sultones

Using a general procedure for the careful fluorination of sulfur-containing compounds, 1,2-oxathiane 2,2-dioxide 16 can be successfully fluorinated by treating the sultone with a mixture of elemental fluorine and helium gas at —78 °C for 8h, after which the crude reaction product is collected and fractionated in cooled traps <1991IC789>. The perfluoro sultone, that resulted, was isolated and characterized by and NMR spectroscopy, and MS. 

Perfluorinated acid fluorides containing heteratoms are also accessible by ECF. Long-chain perfluorinated acid fluorides produced by ECF containing nitrogen (10—12), oxygen (13), and sulfur (14,15) have been reported. The fluorinated mixed sulfonic acid—carboxyflc acid precursors are also known. ECF of hydrocarbon sultones has led to formation of FS02(CF2) C0F, where n = 2,3 (16). 

Octafluoroisobtttylene, whose double bond has reduced electron density and limited accessibility, reacts with sulfur tnoxidg under vigorous conditions The reaction mixture contains various components including bis-oi-tnfluorometh-yldifluoroethane-P-sultone, bis(a-trifluoromethyldifluoroethane)-(i-pyrosultone, the heptafluoroisobutenyl ester of fluorosulfonic acid, and the heptafluoroiso-butenyl ester of fluoropyrosulfomc acid [73] (equation 4)... 

The mechanism and synthetic scope of reactions of monohaptopropargyl-iron complexes has been described earlier (see Schemes 30-33 in Section IV,A,2). By using sulfur dioxide and sulfur trioxide as electrophilic reagents, it is possible to synthesize metal-containing heterocycles in the reduced 1,2-oxathiole category (sultines and sultones) (Scheme 119).182-184 An... 

The present review is concerned with four-membered heterocycles that contain one sulfur atom either alone or associated with another heteroatom. The classes of compounds that will be discussed are the thietanes (1) and thietes (2), the 1,2-oxathietanes (3), the / -sultines and -sultones (4 and 5), the 1,2- and 1,3-thiazetidines (6 and 7) and thiazetes (8), the 1,2- and 1,3-thia-phosphetanes (9 and 10), and the 1,3-silathietanes and 1,3-selenathietanes (11 and 12). 

SULFOXIDES. Sulfoxides arc compounds that contain a sulfinyl group covalently bonded at the sulfur atom to two carbon atoms. They have the general formula RSfO)R, ArS(OtAr, and ArS(Q)R, where Ar and Ar = aryl. Sulfoxides represent an intermediate oxidation level between sulfides and sulfottes. The naturally occurring sulfoxides often are accompanied by the corresponding sulfides or sultones. The only commercially important sulfoxide is the simplest member, dimethyl sulfoxide (DMSO) or sulfinylbismethatie. 

Sultones are useful heterocycles which may be synthesized, in up to 80% yield, simply by treatment of conjugated dienes with sulfur trioxide at low temperatures (equation 208)723. Other alkene-containing molecules react with sulfur trioxide to give a- and /J-sultones724. 

The following four-membered ring heterocycles 1-5, which contain one oxygen and one sulfur atom, are known. Of these the 1,2-oxathietanes are quite common with numerous examples of their oxidised forms, namely the /3-sultines and the /3-sultones, reported over the decades. These systems will form the major part of this chapter. 1,2-Oxathietes, 1,3-oxathietanes, and their S-oxides are still quite rare but examples have been reported and will be highlighted within the chapter where appropriate. 

The most important use of /3-sultones is for the preparation of fluorinated polymers such as Nafion 64. These solid acid catalysts containing perfluorinated sulfonic acid groups have been known for many years and the presence of the electron-withdrawing F atoms increases the acid strength of the terminal sulfonic acid groups, which become comparable to that of pure sulfuric acid. Prior to the last decade, Nafion had been in use as a superacid, a fuel cell electrolyte and as a membrane-ion separator <1996CHEC-II(1B)1083>. 

Sulfur trioxide reacts with fluoroolefins, producing /3-sultones (256). At least two /3-sultones containing the SF5 group are well characterized and will be described here, along with their utility in preparing the desired sulfonic acids or their derivatives. The reader is referred to a review by Gard (259) on /3-fluorosultones. 

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