Fluoroantimonic acid 3465676 221151254 2008-06-23T07:24:28Z Thijs!bot 1392310 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]]