Protonation of alkanes with superacids

Superacids are acids stronger that 100% sulphuric acid. A superacid for protonation of alkanes can be made from hydrofluoric acid, HF, a strong Brønsted acid.

However, its acidity may be dramatically increased by adding the Lewis acid antimonpentafluoride (SbF₅) which binds F^- strongly and displaces the equilibrium strongly far to the right.

Superacids can be more that 10¹⁸ times stronger that 100% sulphuric acid. The solvents used for such acids are compounds with extremely low basicity e.g. SO₂, SO₂C1F and SO₂F₂.
    Olah and the Dutch chemist H. Hogeveen showed independently at the end of the 1960s that superacids such as HF:SbF₅ may cause protons to bind to alkanes. Methane, for example, gives CH₅⁺. This discovery opened up a whole new chemistry for building up, breaking down and isomerizing molecules.

Protonation of methane followed by elimination of H₂.

The methyl cation so obtained then attacks a new molecule of methane and protonated ethane is formed.

Elimination of H⁺ yields ethane. Similarly, higher hydrocarbons may be built.