|Jmol-3D images||Image 1|
|Molar mass||236.76 g mol-1|
|GHS hazard statements||H300, H310, H314, H330, H411|
|GHS precautionary statements||P260, P264, P273, P280, P284, P301+310|
|R-phrases||R26, R29, R35|
|S-phrases||(S1/2), S36/37/39, S45, S53, S60, S61|
|Main hazards||Extremely corrosive, Violent hydrolysis|
|Related acids||Antimony pentafluoride
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Fluoroantimonic acid (systematically named fluorium hexafluorostibanuide and fluorium hexafluoridoantimonate(1-)) is an inorganic compound with the chemical formula H
6 (also written H
6]). It is an ionic liquid created by reacting hydrogen fluoride with antimony pentafluoride in stoichiometrically equivalent amounts. Similar acids can be created by using excess antimony pentafluoride. The 1:1 combination forms 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. F-, being a homoassociation product Lewis base of hydrogen fluoride, attacks the molecules of SbF5 to give an adduct. In the fluoronium molecule, the hydrogen fluoride is coordinated to the hydrogen, although the molecule is formally classified as noncoordinating, because it is both a very weak nucleophile and a very weak base.
Despite the proton being called effectively "naked," it is in fact always attached to a hydrogen fluoride molecule through a very weak dative bond, similar to the hydronium cation. However, the weakness of this bond accounts for the system's extreme acidity. Fluoroantimonic acid is 1016 (10 quadrillion) times stronger than 100% sulfuric acid. The acidic proton easily jumps among different anion-clusters, for example, by the Grotthuss mechanism:
- H2F+ + HF HF + H2F+
The reaction to produce fluoroantimonic acid is:
- 2 HF H2F+ + F-
- SbF5 + F- → SbF6-
- SbF5 + 2 HF → SbF6- + H2F+
Note that the second reaction is not in equilibrium, hence, the overall reaction is not in equilibrium. Fluoroantimonic acid thermally decomposes at higher temperatures, however, emitting hydrogen fluoride vapour.
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
- Fluoroantimonic acid (1990) (H0 Value = −31.3)
- Magic acid (1974) (H0 Value = −19.2)
- Carborane superacid (1969) (H0 Value = −18.0)
- Fluorosulfuric acid (1944) (H0 Value = −15.1)
- Triflic acid (1940) (H0 Value = −14.9)
- (CH3)3CH + H+ → (CH3)3C+ + H2
- (CH3)4C + H+ → (CH3)3C+ + CH4
HF-SbF5 has been described as extremely corrosive, toxic, and moisture sensitive.
It reacts violently with water, producing hydrogen fluoride, dioxygen, and trifluoridoantimony. As such, it will fume in humid air.
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