Graphite-Intercalated Superacids

The intercalation process has been a much disputed topic, but there is now sufficient experimental proof that the intercalation step is generally aredox process in which ions 

The catalytic properties of SbF5-graphite have been investigated.205 208 The chemistry is basically the same as that of SbF5 itself with two major differences (i) As a solid, it can be more easily separated from the reaction mixture, and (ii) the 

Cremlyn, Chlorosulfonic Acid A Versatile Reagent, Royal Society of Chemistry, Cambridge, (2002). 

Dungan and J. R. van Wazer, Compilation of Reported 19F NMR Chemical Shifts, 1951 to mid-1967, Wiley-Interscience, New York, 1970. 

Gramstad, Tidsskr. Kjemi. Bergves. Metall. 19, 62 (1959), Chem. Abstr. 54, 66368 (1960). 

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Ways have been found to immobilize and/or to bind su-peracidic catalysts to an otherwise inert solid support. These include graphite intercalated superacids. Graphite possessing a layered structure can form intercalation compounds with Lewis acids such as AsFs and SbFs. These... 

Solid Superacids. Most large-scale petrochemical and chemical industrial processes ate preferably done, whenever possible, over soHd catalysts. SoHd acid systems have been developed with considerably higher acidity than those of acidic oxides. Graphite-intercalated AlCl is an effective sohd Friedel-Crafts catalyst but loses catalytic activity because of partial hydrolysis and leaching of the Lewis acid halide from the graphite. Aluminum chloride can also be complexed to sulfonate polystyrene resins but again the stabiUty of the catalyst is limited. 

Whereas superacid (HF-BF3, HF-SbFs, HF-TaFs, HSOiF-Sbf s, etc.)-cata-lyzed hydrocarbon transformations were first explored in the liquid phase, subsequently solid acid catalyst systems, such as those based on Nafion-H, longer-chain perfluorinated alkanesulfonic acids, fluorinated graphite intercalates, and so on, were also developed and utilized for heterogeneous reactions. The strong acidic nature of zeolites was also explored. 

The HF-SbFs system is known to be a superacid H34). The possible relevance of this to the intercalation process was pointed out by Vogel V12), who first reported on the extremely high electrical conductivity of graphite-SbFj measured normal to the crystallographic c-axis. The measured conductivity was approximately 40 times that of pristine graphite, and 50% greater than that of pure copper. Other workers... 

The difficulties encountered in handling liquid superacids and the need for product separation from catalyst in batch processes have stimulated research in the isomerization of alkanes over solid superacids. The isomerization of 2-methyl- and 3-methylpentane and 2,3-dimethylbutane, using SbF5-intercalated graphite as a catalyst, has been studied in a continuous flow system. ... 

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