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Fluoroantimonic acid HSbF6 is a mixture of hydrogen fluoride and antimony pentafluoride in various ratios. The 1:1 combination affords the strongest known superacid, which has been demonstrated to protonate even hydrocarbons to afford carbocations and H2.
The reaction of hydrogen fluoride (HF) and SbF5 is exothermic. HF releases its proton (H+), and its conjugate base (F−) is sequestered by one of more molecules SbF5 to give the octahedral SbF6−. This anion is classified as noncoordinating, because it is both a very weak nucleophile and a very weak base. The proton effectively becomes "naked", which accounts for the system's extreme acidity. Fluoroantimonic acid is 2×1019 times stronger than 100% sulfuric acid. The reaction of hydrofluoric acid and antimony pentafluoride proceeds as follows
Additional recommended knowledge
Two related products have been crystallised from HF-SbF5 mixtures, and both have been analyzed by single crystal X-ray crystallography. These salts have the formulas [H2F+][Sb2F11−] and [H3F2+][Sb2F11−]. In both salts the anion is Sb2F11−. As mentioned above, SbF6− is classified as weakly basic; the larger monoanion Sb2F11− would be expected to be still weaker.
Comparison with other acids
The following values are based upon the Hammett acidity function. Acidity is indicated by large negative values of H0.
HF-SbF5 is rapidly and explosively decomposed by water. It reacts with virtually all known solvents. A solvent that has proven compatible with HF-SbF5 is SO2ClF. Chlorofluorocarbons have also been used as solvents. Containers for HF-SbF5 are made of Teflon.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Fluoroantimonic_acid". A list of authors is available in Wikipedia.|