Reversible Protonation of Isobutane in Liquid Superacids in Competition with Protolytic Ionization

The deuterium distribution observed in isobutane recovered after short contact times with the DF−SbF 5 superacid at 0 °C shows that a very fast reversible protonation of all C−H bonds occurs before ionization of the alkane, in accord with the Olah σ-basicity concept. Comparison of the amounts of hydrogen with the amount of tert -butyl ions generated during ionization shows that the reaction is purely protolytic in HF containing up to 20 mol % SbF 5, but becomes oxidative at higher concentrations.