Everything about Fluoroantimonic Acid totally explained
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Fluoroantimonic acid HSbF
6 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 H
2.
The reaction of hydrogen fluoride (HF) and SbF
5 is exothermic. HF releases its proton (H
+), and its
conjugate base (F
−) is sequestered by one of more molecules SbF
5 to give the
octahedral SbF
6−. 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 2×10
19 times stronger than 100%
sulfuric acid. The reaction of hydrofluoric acid and antimony pentafluoride proceeds as follows
Structure
Two related products have been crystallised from HF-SbF
5 mixtures, and both have been analyzed by single crystal X-ray
crystallography. These salts have the formulas [H
2F
+][Sb
2F
11−] and [H
3F
2+][Sb
2F
11−]. In both salts the anion is Sb
2F
11−. As mentioned above, SbF
6− is classified as weakly basic; the larger monoanion Sb
2F
11− 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 H
0.
Applications
This extraordinarily strong acid protonates nearly all
organic compounds. In 1967, Bickel and Hogeveen showed that HF-SbF
5 will remove H
2 from
isobutane and methane from
neopentane:
» (CH
3)
3CH + H
+ → (CH
3)
3C
+ + H
2
(CH
3)
4C + H
+ → (CH
3)
3C
+ + CH
4
Safety
HF-SbF
5 is rapidly and explosively decomposed by water. It reacts with virtually all known solvents.
[ Solvents that have been proven to be compatible with HF-SbF5 are SO2ClF and liquified sulfur dioxide. Chlorofluorocarbons have also been used as solvents. Containers for
HF-SbF5 are made of PTFE.]
Further Information
Get more info on 'Fluoroantimonic Acid'.
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