Fluoroantimonic acid
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2008-06-23T07:24:28Z
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robot Adding: [[es:Ácido fluoroantimónico]]
{{Chembox new
| Name = Fluoroantimonic acid
| ImageFile = Fluoroantimonic-acid-3D-vdW.png
<!-- | ImageSize = 150px -->
| ImageName = Fluoroantimonic acid
| IUPACName = Fluoroantimonic acid
| OtherNames =
| Section1 = {{Chembox Identifiers
| CASNo = 16950-06-4
}}
| Section2 = {{Chembox Properties
| Formula = HSbF<sub>6</sub>
| MolarMass = 236.808 g/mole
| Appearance = colourless syrup
| Density = g cm<sup>–3</sup>
| Solubility = decomposes
| MeltingPt = °C at mmHg
| BoilingPt = decomposes
| pKa = −25
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS =
| MainHazards = corrosive
| FlashPt = non-flammable
| RPhrases = R39/23/24/25-35<!-- Please alter if incorrect -->
| SPhrases =
}}
| Section8 = {{Chembox Related
| Function = [[acid]]s
| OtherFunctn = [[hydrogen fluoride|HF]]</br>[[antimony pentafluoride|SbF<sub>5</sub>]]</br>[[Magic acid]]
| OtherCations = NaPF<sub>6</sub>, NaSbF<sub>6</sub>
| OtherAnions = [[Fluoroboric acid|HBF<sub>4</sub>]]
}}
}}
'''Fluoroantimonic acid''' HSbF<sub>6</sub> is a mixture of [[hydrogen fluoride]] and [[antimony pentafluoride]] in various ratios.<ref name=Olah>[[George Olah|Olah]], G. A.; Prakash, G. K. S.; Wang, Q.; Li, X. “Hydrogen Fluoride–Antimony(V) Fluoride” in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI: 10.1002/047084289.</ref> The 1:1 combination affords the strongest known [[superacid]], which has been demonstrated to protonate even [[hydrocarbon]]s to afford [[carbocation]]s and H<sub>2</sub>.
The reaction of hydrogen fluoride (HF) and SbF<sub>5</sub> is exothermic. HF releases its proton (H<sup>+</sup>), and its [[conjugate base]] (F<sup>−</sup>) is sequestered by one of more molecules SbF<sub>5</sub> to give the [[octahedron|octahedral]] SbF<sub>6</sub><sup>−</sup>. This anion is classified as [[noncoordinating anion|noncoordinating]], because it is both a very weak [[nucleophile]] and a very weak [[base (chemistry)|base]]. The [[proton]] effectively becomes "naked", which accounts for the system's extreme acidity. Fluoroantimonic acid is 2×10<sup>19</sup> (20 quintillion) times stronger than 100% [[sulfuric acid]]. The reaction of hydrofluoric acid and antimony pentafluoride proceeds as follows
[[Image:Reaction of HF with SbF5.png|400px]]
==Structure==
Two related products have been crystallised from HF-SbF<sub>5</sub> mixtures, and both have been analyzed by single crystal X-ray [[crystallography]]. These salts have the formulas [H<sub>2</sub>F<sup>+</sup>][Sb<sub>2</sub>F<sub>11</sub><sup>−</sup>] and [H<sub>3</sub>F<sub>2</sub><sup>+</sup>][Sb<sub>2</sub>F<sub>11</sub><sup>−</sup>]. In both salts the anion is Sb<sub>2</sub>F<sub>11</sub><sup>−</sup>.<ref>{{cite journal | author = Mootz, D.; Bartmann, K. | title = The Fluoronium Ions H<sub>2</sub>F<sup>+</sup> and H<sub>3</sub>F<sub>2</sub><sup>+</sup>: Characterization by Crystal Structure Analysis | journal = [[Angewandte Chemie, International Edition in English]] | year = 1988 | volume = 27 | pages = 391–392 | doi = 10.1002/anie.198803911}}</ref> As mentioned above, SbF<sub>6</sub><sup>−</sup> is classified as weakly basic; the larger monoanion Sb<sub>2</sub>F<sub>11</sub><sup>−</sup> 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<sub>0</sub>.
* Fluoroantimonic acid (1990) (H<sub>0</sub> Value = −31.3)
* [[Magic acid]] (1974) (H<sub>0</sub> Value = −19.2)
* [[Carborane superacid]] (1969) (H<sub>0</sub> Value = −18.0)
* [[Fluorosulfuric acid]] (1944) (H<sub>0</sub> Value = −15.1)
* [[Triflic acid]] (1940) (H<sub>0</sub> Value = −14.9)
==Applications==
{{main|Superacid#Applications}}
This extraordinarily strong acid protonates nearly all [[organic compound]]s. In 1967, Bickel and Hogeveen showed that HF-SbF<sub>5</sub> will remove H<sub>2</sub> from [[isobutane]] and methane from [[neopentane]]:<ref>{{cite journal | author = Bickel, A. F.; Gaasbeek, C. J.; Hogeveen, H.; Oelderik, J. M.; Platteeuw, J. C. | title = Chemistry and spectroscopy in strongly acidic solutions: reversible reaction between aliphatic carbonium ions and hydrogen | journal = [[Chemical Communications]] | year = 1967 | volume = 1967 | pages = 634–5 | doi = 10.1039/C19670000634}}</ref><ref>{{cite journal | author = Hogeveen, H.; Bickel, A. F. | title = Chemistry and spectroscopy in strongly acidic solutions: electrophilic substitution at alkane-carbon by protons | journal = [[Chemical Communications]] | year = 1967 | volume = 1967 | pages = 635–6 | doi = 10.1039/C19670000635}}</ref>
:(CH<sub>3</sub>)<sub>3</sub>CH + H<sup>+</sup> → (CH<sub>3</sub>)<sub>3</sub>C<sup>+</sup> + H<sub>2</sub>
:(CH<sub>3</sub>)<sub>4</sub>C + H<sup>+</sup> → (CH<sub>3</sub>)<sub>3</sub>C<sup>+</sup> + CH<sub>4</sub>
==Safety==
HF-SbF<sub>5</sub> is rapidly and explosively decomposed by water. It reacts with virtually all known solvents.<ref name=Olah/> [[solvent|Solvents]] that have been proven to be compatible with HF-SbF<sub>5</sub> are [[sulfuryl chloride fluoride|SO<sub>2</sub>ClF]] and liquified [[sulfur dioxide]]. Chlorofluorocarbons have also been used as solvents. Containers for
HF-SbF<sub>5</sub> are made of [[Polytetrafluoroethylene|PTFE]].
==References==
<references/>
[[Category:Antimony compounds]]
[[Category:Fluorides]]
[[Category:Inorganic compounds]]
[[Category:Superacids]]
[[de:Fluor-Antimonsäure]]
[[es:Ácido fluoroantimónico]]
[[fr:Acide fluoroantimonique]]
[[he:חומצה פלואורואנטימונית]]
[[pl:Kwas fluoroantymonowy]]
[[pt:Ácido fluorantimônico]]
[[fi:Fluoriantimonihappo]]
[[zh:氟銻酸]]