What is "fluoroantimonic acid"

n. An ionic liquid created by reacting hydrogen fluoride with antimony pentafluoride in stoichiometrically equivalent amounts.

Fluoroantimonic acid (systematically named fluoranium hexafluorostibanuide and fluoranium hexafluoridoantimonate(1−)) is an inorganic compound with the chemical formula (also written , 2HF·SbF, or simply HF-SbF). It is an ionic liquid created by reacting hydrogen fluoride (HF) with antimony pentafluoride (SbF) in a stoichiometric ratio of 2:1. It is the strongest known superacid, which has been demonstrated to protonate even hydrocarbons to afford pentacoordinate carbocations (which decompose quickly in regular carbocations and H). Similar acids can be created by using excess antimony pentafluoride.

The reaction to produce fluoroantimonic acid is:

2 HF HF + F SbF + F →

The overall reaction is:

SbF + 2 HF → + HF

The second reaction is not in equilibrium, therefore the overall reaction is not in equilibrium. The reaction is exothermic.

The F, produced by autoionization of hydrogen fluoride, reacts with SbF to yield the adduct . In the fluoronium ion, hydrogen fluoride is coordinated to the hydrogen ion. The anion is classified as noncoordinating and is both a very weak nucleophile and a very weak base.

The acid is often said to contain " naked protons", but the "free" protons are, in fact, always bonded to hydrogen fluoride molecules to make the fluoronium cations (similar to the hydronium cation in aqueous solution). It is the fluoronium ion that accounts for fluoroantimonic acid's extreme acidity. Fluoroantimonic acid is 10 (10 quadrillion) times stronger than 100% sulfuric acid. The protons easily migrate through the solution, moving from HF to HF, when present, by the Grotthuss mechanism:

HF + HF HF + HF

Fluoroantimonic acid thermally decomposes at higher temperatures, generating hydrogen fluoride gas.