Superacid-Catalyzed Reactions

In discussing superacids as catalysts for chemical reactions, we will review both liquid (Magic Acid, fluoroantimonic acid, etc.) and solid (Nafion-H, etc.) acid-catalyzed reactions, but not those of conventional Friedel-Crafts-type catalysts. The latter reactions have been extensively reviewed elsewhere (see G. A. Olah, Friedel-Crafts Chemistry, Wiley, New York, 1972 G. A. Olah, ed., Friedel-Crafts and Related Reactions, Vols. I-IV, Wiley-Interscience, New York, 1963-1965). 

As already mentioned and shown, considerable experimental and theoretical evidence has been collected over the last decades, which supports the idea of superelectrophilic activation, that is, protosolvation1 2 or de facto protonation of cationic intermediates.3-5 Examples of superelectrophiles as highly reactive dica-tionic (doubly electron-deficient) and tricationic intermediates were discussed in Chapter 4. 

The success of carbocation chemistry lies in the stabilization of carbocations in a medium of low nucleophilicity. Superelectrophiles, in turn, are reactive intermediates generated by further protonation (protosolvation). This second protonation increases electron deficiency, induces destabilization, and, consequently, results in a profound increase in reactivity. In particular, charge-charge repulsive interactions6 play a crucial role in the enhanced reactivity of dicationic and tricationic superelectrophilic intermediates. As various examples of acidity dependence studies show, without an appropriate acidity level, transformations may occur at much lower rate or even do not take place at all. In addition to numerous examples of superacid catalyzed reactions, various organic transformations, in which the involvement of superelectrophilic intermediates is invoked or superelectrophiles are de facto observed in the condensed state, are also included in this chapter. 

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Many superacid-catalyzed reactions were found to be carried out advantageously not only using liquid superacids but also over solid superacids, including Nafion-H or certain zeolites. We extensively studied the catalytic activity of Nafion-H and related solid acid catalysts (including supported perfluorooctanesulfonic acid and its higher ho-... 

The hydrocarbon research program of the Toker Institute was able in many ways to build on and utilize results of our fundamental work on superacid-catalyzed reactions and their mechanistic aspects (includ-... 

Because the protonation of ozone removes its dipolar nature, the electrophilic chemistry of HOs, a very efficient oxygenating electrophile, has no relevance to conventional ozone chemistry. The superacid-catalyzed reaction of isobutane with ozone giving acetone and methyl alcohol, the aliphatic equivalent of the industrially significant Hock-reaction of cumene, is illustrative. 

Zhang, Y. Briski, J. Zhang, Y. Rendy, R. Klumpp, D. A. Superacid-Catalyzed Reactions of Olefinic Pyrazines an Example of Anti-Markovnikov Addition Involving Superelectrophiles. Org. Lett. 2005, 7, 2505-2508. 

Some of the most important reaction intermediates in organic chemistry are the carbocations. Neglecting some heteroatom-stabilized cations, most carbocations are divided into two groups trivalent carbenium ions and five-coordinate or higher coordinate carbonium ions. The parent carbenium ion is CHJ, and the parent carbonium ion is CHJ. Carbonium ions have been proposed as reactive intermediates in superacid-catalyzed reactions however, they have never been directly observed in condensed media. In contrast, a variety of carbenium ions have already been prepared in superacidic media and been characterized by various physical methods, mainly 13C NMR spectroscopy (5). 

The superacid-catalyzed reaction is thus alkylation of the methane with the ethyl cation. 

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