Super acids reaction with hydrocarbons

Hydrocarbons undergo related reaction.s in the super-acid media, such as fluorosuiphuric acid and antimony pentachloride. It has been suggested that the initial one-electron processes during the electrochemical oxidation of alkanes in fluorosuiphuric acid involve a protonated carbon-hydrogen bond with formation of a carbon radical and release of two protons [15]. 

R H) is much faster than alkylation, so that alkylation products are also derived from the new alkanes and carbocations formed in the exchange reaction. Furthermore, the carbo-cations present are subject to rearrangement (Chapter 18), giving rise to new carbocations. Products result from all the hydrocarbons and carbocations present in the system. As expected from their relative stabilities, secondary alkyl cations alkylate alkanes more Teadily than tertiary alkyl cations (the r-butyl cation does not alkylate methane or ethane). Stable primary alkyl cations are not available, but alkylation has been achieved with complexes formed between CH3F or C2H5F and SbFs-212 The mechanism of alkylation can be formulated (similar to that shown in hydrogen exchange with super acids, 2-1) as... 

It is important to point out that thermodynamic equilibria of hydrocarbons and those of derived carbocations are substantially different. Under appropriate conditions (traditional acid catalysts, longer contact time), the thermodynamic equilibrium mixture of hydrocarbons can be reached. In contrast, when a reaction mixture in contact with excess of strong (super) acid is quenched, a product distribution approaching the thermodynamic equilibrium of the corresponding carbocations may be obtained. The two equilibria can be very different. Since a large energy difference in the stability of primary < secondary < tertiary carbocations exists, in excess of superacid solution, generally the most stable tertiary cations predominate. This allows, for example, isomerization of n-butane to isobutane to proceed past the equilibrium concentrations of the neutral hydrocarbons, as the er -butyl cation is by far the most stable butyl cation. 

If acidity functions of -20 to -30 are accessible with super acids, can one protonate alkanes The answer is "yes", and in fact, the 1994 Nobel Prize in Chemistry presented to George Olah was partially in acknowledgement of this discovery. The realization of cr bond basicity led to the ability to activate hydrocarbons at low temperature toward various reactions. 

Alkylation with Unsaturated Hydrocarbons. CH4 is thermodynamically favorable to react with lower olefins to form higher paraffins using super-acids (Sommer et al. (1982), and Olah et al. (1983)) according to the following reaction with C2H4 ... 

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