Fluoroantimonic Acid - Wikipedia

Chemical compound Fluoroantimonic acid

Fluoroantimonic acid stored in a PFA bottle
Names
IUPAC name Fluoroantimonic acid
Systematic IUPAC name Hexafluoroantimonic acid
Other names Fluoroantimonic(V) acid Hydrogen Fluoroantimonate Hydrogen Hexafluoroantimonate Fluoronium Fluoroantimonate Fluoronium Hexafluoroantimonate
Identifiers
CAS Number	16950-06-4 (HSbF6) N
3D model (JSmol)	Interactive image
ChemSpider	32741664 N
ECHA InfoCard	100.037.279
EC Number	241-023-8
PubChem CID	11118066 wrong formula
CompTox Dashboard (EPA)	DTXSID10894750
InChI InChI=1S/FH2.6FH.Sb/h1H2;6*1H;/q+1;;;;;;;+5/p-6 NKey: HBGBSIVYTBPVEU-UHFFFAOYSA-H N
SMILES [FH2+].F[Sb-](F)(F)(F)(F)F
Properties
Molar mass	236.756 g/mol
Appearance	Colorless liquid
Density	2.885 g/cm3
Boiling point	40 °C (104 °F; 313 K) (decomposes)
Solubility in water	reacts
Solubility in sulfuryl chloride fluoride	soluble
Solubility in sulfur dioxide	soluble
Vapor pressure	19 hPa (18 °C (64 °F; 291 K))
Hazards[1]
Occupational safety and health (OHS/OSH):
Main hazards	Extremely corrosive, toxic, Violent hydrolysis.
GHS labelling:[2]
Pictograms
Signal word	Danger
Hazard statements	H300+H310+H330, H314, H411
Precautionary statements	P260, P262, P264, P270, P271, P273, P280, P284, P301+P310+P330, P301+P330+P331, P302+P350, P303+P361+P353, P304+P340+P310, P305+P351+P338+P310, P362, P391, P403+P233, P405, P501
NFPA 704 (fire diamond)	4 0 4WOX
Threshold limit value (TLV)	0.5 mg/m3 (TWA)
NIOSH (US health exposure limits):[2]
PEL (Permissible)	0.5 mg/m3
REL (Recommended)	0.5 mg/m3 (TWA)
Related compounds
Related acids	Antimony pentafluoride Hydrogen fluoride Magic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Chemical compound

Fluoroantimonic acid is a mixture of hydrogen fluoride and antimony pentafluoride, containing various cations and anions, the simplest being fluoronium (H2F+) and fluoroantimonate (SbF−6). The mixture is the strongest known superacid, stronger than pure sulfuric acid by many orders of magnitude, according to its Hammett acidity function. It even protonates some hydro­carbons to afford pentacoordinate carbo­cations (carbonium ions).[3] Like its precursor hydrogen fluoride, it attacks glass, but can be stored in containers lined with PTFE (Teflon) or PFA.[citation needed]

Chemical composition

[edit]

Fluoroantimonic acid is formed by combining hydrogen fluoride and antimony pentafluoride:

SbF5 + 2 HF ⇌ SbF−6 + H2F+

The speciation (i.e., the inventory of components) of fluoroantimonic acid is complex. Spectroscopic measurements show that fluoroantimonic acid consists of a mixture of HF-solvated protons, [(HF)nH]+ (such as H3F+2), and SbF5-adducts of fluoride, [(SbF5)nF]− (such as Sb4F−21). Thus, the formula "[H2F]+[SbF6]−" is a convenient but oversimplified approximation of the true composition.[4]

Nevertheless, the extreme acidity of this mixture is evident from the inferior proton-accepting ability of the species present in solution. Hydrogen fluoride, a weak acid in aqueous solution that is normally not thought to have any appreciable Brønsted basicity at all, is in fact the strongest Brønsted base in the mixture, protonating to H2F+ in the same way water protonates to H3O+ in aqueous acid. It is the fluoronium ion that accounts for fluoroantimonic acid's extreme acidity. The protons easily migrate through the solution, moving from H2F+ to HF, when present, by the Grotthuss mechanism.[5]

Two related products have been crystallized from HF−SbF5 mixtures, and both have been analyzed by single crystal X-ray crystallography. These salts have the formulas [H2F+] [Sb2F−11] and [H3F+2] [Sb2F−11]. In both salts, the anion is Sb2F−11. As mentioned above, SbF−6 is weakly basic; the larger anion Sb2F−11 is expected to be a still weaker base.[6]

Acidity

[edit]

Fluoroantimonic acid is the strongest superacid based on the measured value of its Hammett acidity function (H0), which has been determined for various ratios of HF:SbF5. The H0 of HF is −15.1±0.1 (Instead of around -11 as previously determined) Gillespie et al. accurately measured the Hammett acidity of a series of pentafluorides in anhydrous hydrogen fluoride in 1988, demonstrating that the anhydrous hydrogen fluoride solution of pentafluoride (i.e. "fluoroantimonic acid") has stronger acidity than the fluorosulfonic acid solution.[7] Solutions of HF have H0 values ranging from −20 to −22±1 as the molar percentage of SbF5 rises from 1% to over 50%. The lowest attained H0 is about −28 (although some sources have reported values below −31.)[8][9]

The following H0 values provide a comparison to other superacids.[10]

Acidities of selected superacids[a]
Compound	H0 (high value)	H0 (low value)
Fluoroantimonic acid	−23	−28
Magic acid	−23
Carborane acid	−18	-
Fluorosulfuric acid	−15
Triflic acid	−15
Perchloric acid	−13

1. ^ Increased acidity is indicated by lower (in this case, more negative) values of H0.

Of the above, only the carborane acids, whose H0 could not be directly determined due to their high melting points, may be stronger acids than fluoroantimonic acid.[10][11]

The H0 value measures the protonating ability of the bulk, liquid acid, and this value has been directly determined or estimated for various compositions of the mixture. The pKa on the other hand, measures the equilibrium of proton dissociation of a discrete chemical species when dissolved in a particular solvent. Since fluoroantimonic acid is not a single chemical species, its pKa value is not well-defined.[citation needed]

The gas-phase acidity (GPA) of individual species present in the mixture have been calculated using density functional theory methods.[4] (Solution-phase pKas of these species can, in principle, be estimated by taking into account solvation energies, but do not appear to be reported in the literature as of 2019.) For example, the ion-pair [H2F]+·[SbF6]− was estimated to have a GPA of 1,060 kJ/mol. For comparison, the commonly encountered superacid triflic acid, TfOH, is a substantially weaker acid by this measure, with a GPA of 1,250 kJ/mol.[12] However, certain carborane superacids have GPAs lower than that of [H2F]+·[SbF6]−. For example, H(CHB11Cl11) has an experimentally determined GPA of 1,010 kJ/mol.[13]

Reactions

[edit]

Fluoroantimonic acid solution is so reactive that it is challenging to identify media where it is unreactive. Materials compatible as solvents for fluoroantimonic acid include sulfuryl chloride fluoride (SO2ClF), and sulfur dioxide (SO2); some chlorofluorocarbons have also been used. Containers for HF−SbF5 are made of PTFE.[citation needed]

Fluoroantimonic acid solutions decompose when heated, generating free hydrogen fluoride gas and liquid antimony pentafluoride at a temperature of 40 °C (104 °F).[citation needed]

As a superacid, fluoroantimonic acid solutions protonate nearly all organic compounds, often causing dehydrogenation, or dehydration. In 1967, Bickel and Hogeveen showed that 2HF·SbF5 reacts with isobutane and neopentane to form carbenium ions:[14][15]

(CH3)3CH + H+ → (CH3)3C+ + H2 (CH3)4C + H+ → (CH3)3C+ + CH4

It is also used in the synthesis of tetraxenonogold complexes.[16]

Safety

[edit]

HF−SbF5 is a highly corrosive substance that reacts violently with water. Heating it is dangerous as well, as it decomposes into toxic hydrogen fluoride.

See also

[edit]

• Fluoroboric acid
• Fluorosulfuric acid
• Hexafluorophosphoric acid

References

[edit]

1. ^ "SDS - Hydrogen hexafluoroantimonate(V), ca 65% aqueous solution". fishersci.com. ThermoFisher Scientific. 1 April 2024. Retrieved 7 November 2025.
2. ^ a b Sigma-Aldrich Co., Fluoroantimonic acid.
3. ^ Olah, G. A. (2001). A Life of Magic Chemistry: Autobiographical Reflections of a Nobel Prize Winner. John Wiley and Sons. pp. 100–101. ISBN 978-0-471-15743-4.
4. ^ a b Esteves, Pierre M.; Ramírez-Solís, Alejandro; Mota, Claudio J. A. (March 2002). "The Nature of Superacid Electrophilic Species in HF/SbF5: A Density Functional Theory Study". Journal of the American Chemical Society. 124 (11): 2672–2677. doi:10.1021/ja011151k. ISSN 0002-7863. PMID 11890818.
5. ^ Klein, Michael L. (October 25, 2000). "Getting the Jump on Superacids" (PDF). Pittsburgh Supercomputing Center (PSC). Archived from the original (PDF) on May 31, 2012. Retrieved 2012-04-15.
6. ^ Mootz, Dietrich; Bartmann, Klemens (March 1988). "The Fluoronium Ions H2F+ and H3F+2: Characterization by Crystal Structure Analysis". Angewandte Chemie International Edition. 27 (3): 391–392. doi:10.1002/anie.198803911.
7. ^ Gillespie, Ronald J.; Liang, Jack. (1988-08-01). "Superacid solutions in hydrogen fluoride". Journal of the American Chemical Society. 110 (18): 6053–6057. doi:10.1021/ja00226a020. ISSN 0002-7863.
8. ^ Superacid chemistry. Olah, George A. (George Andrew), 1927–2017., Olah, George A. (George Andrew), 1927–2017. (2nd ed.). Hoboken, N.J.: Wiley. 2009. ISBN 9780470421543. OCLC 391334955.{{cite book}}: CS1 maint: others (link)
9. ^ Olah, G. A. (2005). "Crossing Conventional Boundaries in Half a Century of Research". Journal of Organic Chemistry. 70 (7): 2413–2429. doi:10.1021/jo040285o. PMID 15787527.
10. ^ a b Gillespie, R. J.; Peel, T. E. (1973-08-01). "Hammett acidity function for some superacid systems. II. Systems sulfuric acid-[fsa], potassium fluorosulfate-[fsa], [fsa]-sulfur trioxide, [fsa]-arsenic pentafluoride, [sfa]-antimony pentafluoride and [fsa]-antimony pentafluoride-sulfur trioxide". Journal of the American Chemical Society. 95 (16): 5173–5178. doi:10.1021/ja00797a013. ISSN 0002-7863.
11. ^ Olah, G. A.; Prakash, G. K. Surya; Wang, Qi; Li, Xing-ya (15 April 2001). "Hydrogen Fluoride–Antimony(V) Fluoride". Encyclopedia of Reagents for Organic Synthesis. New York: John Wiley and Sons. doi:10.1002/047084289X.rh037m. ISBN 9780470842898.
12. ^ Koppel, Ilmar A.; Burk, Peeter; Koppel, Ivar; Leito, Ivo; Sonoda, Takaaki; Mishima, Masaaki (May 2000). "Gas-Phase Acidities of Some Neutral Brønsted Superacids: A DFT and ab Initio Study". Journal of the American Chemical Society. 122 (21): 5114–5124. doi:10.1021/ja0000753. ISSN 0002-7863.
13. ^ Meyer, Matthew M.; Wang, Xue-bin; Reed, Christopher A.; Wang, Lai-Sheng; Kass, Steven R. (2009-12-23). "Investigating the Weak to Evaluate the Strong: An Experimental Determination of the Electron Binding Energy of Carborane Anions and the Gas phase Acidity of Carborane Acids". Journal of the American Chemical Society. 131 (50): 18050–18051. doi:10.1021/ja908964h. ISSN 0002-7863. PMID 19950932. S2CID 30532320.
14. ^ Bickel, A. F.; Gaasbeek, C. J.; Hogeveen, H.; Oelderik, J. M.; Platteeuw, J. C. (1967). "Chemistry and spectroscopy in strongly acidic solutions: reversible reaction between aliphatic carbonium ions and hydrogen". Chemical Communications. 1967 (13): 634–635. doi:10.1039/C19670000634.
15. ^ Hogeveen, H.; Bickel, A. F. (1967). "Chemistry and spectroscopy in strongly acidic solutions: electrophilic substitution at alkane-carbon by protons". Chemical Communications. 1967 (13): 635–636. doi:10.1039/C19670000635.
16. ^ Konrad Seppelt, Stefan Seidel; Seppelt, K (2000-10-06). "Xenon as a Complex Ligand: The Tetraxenonogold(II) Cation in AuXe2+4(Sb2F−11)2". Science. 290 (5489): 117–118. Bibcode:2000Sci...290..117S. doi:10.1126/science.290.5489.117. PMID 11021792.

v t e Hydrogen compounds

H3AsO3 H3AsO4 HArF HAt HSO3F H[BF4] HBr HBrO HBrO2 HBrO3 HBrO4 HCl HClO HClO2 HClO3 HClO4 HCN HCNO H2CrO4/H2Cr2O7 H2CO3 H2CS3 HF HFO HI HIO HIO2 HIO3 HIO4 HMnO4 H2MnO4 H2MoO4 HNC NaHCO3 HNCO HNO HNO2 HNO3 H2N2O2 HNO5S H3NSO3 H2O H2O2 H2O3 H2O4 H2O5 H3PO2 H3PO3 H3PO4 H4P2O7 H5P3O10 H[AuCl4] H2[PtCl6] H2OsCl6 H2S H2S2 H2Se H2SeO3 H2SeO4 H4SiO4 H2[SiF6] HSCN HNCS H2SO3 H2SO4 H2SO5 H2S2O3 H3O H2S2O6 H2S2O7 H2S2O8 CF3SO3H H2Te H2TeO3 H6TeO6 H4TiO4 H2Po H[Co(CO)4]

v t e Antimony compounds
Antimonides	AlSb Bi1-xSbx DySb GaSb HoSb HoSb2 InSb PrSb SmSb YSb ZnSb
Sb(III)	SbBr3 Sb(C2H3O2)3 SbCl3 SbF3 Sb4O4(OH)2(NO3)2 SbH3 SbI3 SbN Sb2O3 Sb2S3 Sb2(SO4)3 Sb2Se3 Sb2Te3 Organoantimony(III) compounds Sb(CH3)3 Sb(C6H5)3
Sb(III,V)	Sb2O4
Sb(V)	SbCl5 SbF5 Sb2O5 Sb2S5 Organoantimony(V) compounds Sb(CH3)5 Sb(C6H5)5

v t e Fluorine compounds
v t e Salts and covalent derivatives of the fluoride ion HF ?HeF2 LiF BeF2 BFBF3B2F4+BO3 CF4CxFy+CO3 NF3FN3N2F2NFN2F4NF2?NF5+N+NO3 OF2O2F2OFO3F2O4F2?OF4 F2 Ne NaF MgF2 AlFAlF3 SiF4 P2F4PF3PF5+PO4 S2F2SF2S2F4SF3SF4S2F10SF6+SO4 ClFClF3ClF5 ?ArF2?ArF4 KF CaFCaF2 ScF3 TiF2TiF3TiF4 VF2VF3VF4VF5 CrF2CrF3CrF4CrF5?CrF6 MnF2MnF3MnF4?MnF5 FeF2FeF3FeF4 CoF2 CoF3 CoF4 NiF2NiF3NiF4 CuFCuF2?CuF3 ZnF2 GaF2GaF3 GeF2GeF4 AsF3AsF5 Se2F2SeF4SeF6+SeO3 BrFBrF3BrF5 KrF2?KrF4?KrF6 RbF SrFSrF2 YF3 ZrF2ZrF3ZrF4 NbF4NbF5 MoF4MoF5MoF6 TcF4TcF5 TcF6 RuF3RuF4RuF5RuF6 RhF3RhF4RhF5RhF6 PdF2Pd[PdF6]PdF4?PdF6 Ag2FAgFAgF2AgF3 CdF2 InFInF3 SnF2SnF4 SbF3SbF5 TeF4?Te2F10TeF6+TeO3 IFIF3IF5IF7+IO3 XeF2XeF4XeF6?XeF8 CsF BaF2   LuF3 HfF4 TaF5 WF4WF5WF6 ReF4ReF5ReF6ReF7 OsF4OsF5OsF6?OsF7?OsF8 IrF2IrF3IrF4IrF5IrF6 PtF2Pt[PtF6]PtF4PtF5PtF6 AuFAuF3Au2F10?AuF6AuF5•F2 Hg2F2HgF2?HgF4 TlFTlF3 PbF2PbF4 BiF3BiF5 PoF2PoF4PoF6 AtF?AtF3?AtF5 RnF2?RnF4?RnF6 FrF RaF2   LrF3 Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og ↓ LaF3 CeF3CeF4 PrF3 PrF4 NdF2 NdF3 NdF4 PmF3 SmF SmF2 SmF3 EuF2 EuF3 GdF3 TbF3 TbF4 DyF2 DyF3 DyF4 HoF3 ErF3 TmF2 TmF3 YbF2 YbF3 AcF3 ThF2ThF3ThF4 PaF4PaF5 UF3UF4UF5UF6 NpF3NpF4NpF5NpF6 PuF3PuF4PuF5PuF6 AmF2AmF3AmF4?AmF6 CmF3CmF4 ?CmF6 BkF3 BkF4 CfF3 CfF4 EsF3 EsF4?EsF6 Fm MdF3 No
PF−6, AsF−6, SbF−6 compounds	AgPF6 KAsF6 LiAsF6 NaAsF6 HPF6 HSbF6 NH4PF6 LiSbF6 KPF6 KSbF6 LiPF6 NaPF6 NaSbF6 TlPF6
AlF2−5, AlF3−6 compounds	(NH4)3[AlF6] Cs2AlF5 Li3AlF6 K3AlF6 Na3AlF6
chlorides, bromides, iodides and pseudohalogenides	BaClF SiIBrClF BrSO3F Br(SO3F)3 CFN ClFO2 PbFBr PbFCl SrFCl
SiF2−6, GeF2−6 compounds	BaSiF6 BaGeF6 (NH4)2SiF6 Na2[SiF6] K2[SiF6] Li2GeF6 Li2SiF6
Oxyfluorides	AcOF C7H5FO BrOF3 BrO2F ErOF HoOF BrO3F NdOF NpO2F2 LaOF SmOF TbOF ThOF2 VOF3 TcO3F PrOF PuOF PuO2F2 UO2F2 WOF4 C2F4O YOF ClOF3 ClO2F3
Organofluorides	CBrF3 CBr2F2 CBr3F CClF3 CCl2F2 CCl3F CF2O CF3I CHF3 CH2F2 CH3F C2Cl3F3 C2H3F C6H5F C7H5F3 C15F33N C3H5F C6H11F
with transition metal, lanthanide, actinide, ammonium	VOF3 CrOF4 CrF2O2 NH4F (NH4)3CrF6 (NH4)3GaF6 (NH4)2GeF6 (NH4)3FeF6 (NH4)3InF6 NH4NbF6 (NH4)2SnF6 NH4TaF6 (NH4)3VF6 (NH4)2ZrF6 CsXeF7 Li2SnF6 Li2TiF6 LiWF6 Li2ZrF6 K2TiF6 Rb2TiF6 Na2TiF6 Na2ZrF6 K2NbF7 K2TaF7 K2ZrF6 UO2F2
nitric acids	FNO FNO2 FNO3
bifluorides	KHF2 NaHF2 NH4HF2
thionyl, phosphoryl, and iodosyl	FN3O2S F2OS3 F2OS F3OP PSF3 IOF3 IO3F F2O6S2 F2O5S2 FClO5S2 ISO3F IOF5 IO2F IO2F3 I3SO3F S3O8F2
Chemical formulas