|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
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
|(what is: / ?)|
Fluoroantimonic acid (systematically named fluoronium hexafluorostibanuide and fluoronium 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 (HF) with antimony pentafluoride (SbF5) in stoichiometrically equivalent amounts. It is the strongest known superacid, which has been demonstrated to protonate even hydrocarbons to afford carbocations and H2. Similar acids can be created by using excess antimony pentafluoride.
The reaction to produce fluoroantimonic acid is:
- 2 HF H2F+ + F-
- SbF5 + F- → SbF6-
The overall reaction is:
- SbF5 + 2 HF → SbF6- + H2F+
The second reaction is not in equilibrium, therefore the overall reaction is not in equilibrium. The reaction is exothermic.
The F-, a homoassociation product of the Lewis base hydrogen fluoride, attacks the SbF5 molecules, yielding the adduct SbF6-. In the fluoronium ion, 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.
The acid is often said to contain "naked protons", but the freed protons always attach to hydrogen fluoride molecules through very weak dative bonds, making fluoronium cations (similar to the hydronium cations in aqueous solutions). 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 protons easily migrate through the solution, jumping from H2F+ to HF, when present, by the Grotthuss mechanism:
- H2F+ + HF HF + H2F+
Fluoroantimonic acid thermally decomposes at higher temperatures, 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. It will fume in humid air.
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