Superacid - Superlatives and Metaphors

Superlatives and Metaphors

Fluoroantimonic acid, the strongest acid in the system, is 1016 times stronger than 100% sulfuric acid, and can produce solutions with a H₀ down to –28. Fluoroantimonic acid is a combination of hydrofluoric acid and SbF₅. In this system, HF releases its proton (H+) concomitant with the binding of F− by the antimony pentafluoride. The resulting anion (SbF−
6) is both a weak nucleophile and a weak base.

The proton from superacids has been popularly said to become "naked," accounting for the system's extreme acidity. In the physical sense, the acidic "proton" is never completely free (as an unbound proton) in the acid, but rather hops from anion to anion in superacids via the Grotthuss mechanism, just as happens to acidic "protons" in water. The extreme acidity of the acids is due to the ease with which this proton is transferred to substances that cannot normally be "protonated" (such as hydrocarbons), due to the very high stability of the conjugate-base anion (such as SbF−
6) after it donates the proton.