Alkanesulfonyl fluorides

Perfluoroalkanesulfonyl fluorides and of related materials are manufactured by the electrochemical fluorination of the corresponding alkanesulfonyl fluorides or cyclic sulfonesP This electrochemical synthesis results in replacement of all C-H bonds in the feedstock. The perfluorinated alkanesulfonyl fluoride products are neutralized to make the anhydrous salt, then acidified and distilled to afford the anhydrous sulfonic acid. Alkyl chain degradation in the electrochemical cell becomes more pronounced at longer chain lengths. Addition of short-chain divalent sulfur compounds (e.g., thiols, sulfides) to the cell inhibits buildup of tarry materials and loss of efficiency. 

Perfluoroalkanesulfonic acids are mainly prepared by two methods. The first method based on electrochemical fluorination (ECF) in anhydrous hydrogen fluoride (AHF) is the most practical. Although fluorination of the alkanesulfonic acids cannot be carried out directly by ECF9,10, the alkanesulfonyl fluorides can be successfully fluorinated with fairly high yields. The prefluorinated sulfonyl fluoride produced may then be converted to the corresponding salt by alkaline hydrolysis. The free acids were obtained either by their distillation from a solution of the alkaline metal sulfonate in concentrated sulfuric acid or by treatment of the salt with strong acid-type ion exchange resin (equation 1). 

Methanesulfonyl fluoride, CH3S02F, and other alkanesulfonyl fluorides were prepared by Davies and Dick, 1932, by refluxing CH3S02C1 over solid ZnF2 or by heating an alkanesulfonyl chloride with 70% KF solution in water (63). 

Nitration alkanesu onyl fluorides. Swiss chemists have repotted two examples in which reactions are carried out successfully in 80-98% aqueous hydrofluoric acid. One is the nitration of anthraquinone with nitric acid or dinitrogen tetroxide in 80-98% aqueous hydrofluoric acid at 30-40°. The other is oxidation of aliphatic thiols to alkanesulfonyl fluorides with nitrogen dioxide in aqueous 80-98% HF. 

Alkaneboronic acids, 34 Alkanesulfonyl fluorides, 284 Alkeneboronic acids, 34... 

The alkanesulfonic acids themselves are not suitable starting materials for electrochemical fluorination because the yields of perfluoroalkanesulfonic acids obtained from the free acids are much lower compared to the alkanesulfonyl fluorides and chlorides. Another major disadvantage of this approach is the formation of water, which may result in the formation of explosive oxygen difluoride (OF2). 

Fluorination of alkanesulfonyl fluorides or chlorides gives higher yields of perfluoroalkanesulfonic acids than fluorination of alkanesulfonic acids [49,51,52,54]. Another disadvantage associated with the fluorination of free alkanesulfonic acids is the potential explosion hazard caused by excessive amounts of oxygen difluoride and hypofluorites formed as by-products [55]. 

Fluorinated and Ghlorfluorinated Sulfonic Acids. The synthesis of chlorinated and fluorinated sulfonic acids has been extensively reviewed (91,92). The Hterature discusses the reaction of dialkyl sulfides and disulfides, sulfoxides and sulfones, alkanesulfonyl haHdes, alkanesulfonic acids and alkanethiols with oxygen, hydrogen chloride, hydrogen fluoride, and oxygen—chloride—hydrogen fluoride mixtures over metal haHde catalysts, such as... 

Sulfenes generated from alkanesulfonyl chlorides and tertiary amines have not been observed to react with simple olefins or dienes1,36, but Block and Aslam98 reported that sulfene from (trimethylsilyl) methanesulfonyl chloride with cesium fluoride reacted with dienes to afford [4 + 2] cycloadducts (equation 110). Slightly greater yields of the... 

Electrochemical fluorination of alkanesulfonyl chlorides or fluorides yields the corresponding perfluorosulfonyl chloride or fluoride in a 12-79% yield, depending on the alkane chain length [51] ... 

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