Fluorosulfuric acid

Fluorosulfuric acid
Names
IUPAC name
Sulfurofluoridic acid
Systematic IUPAC name
Fluorosulfuric acid
Other names
Fluorosulfonic acid,
Fluorosulphonic acid,
Fluorinesulfonic acid,
Fluorinesulphonic acid,
Fluoridosulfonic acid,
Fluoridosulphonic acid,
Sulfuric fluorohydrin,
Epoxysulfonyl fluoride
Identifiers
7789-21-1 YesY
ChemSpider 23005 YesY
EC Number 232-149-4
Jmol 3D model Interactive image
Interactive image
MeSH Fluorosulfonic+acid
PubChem 24603
RTECS number LP0715000
UN number 1777
Properties
FHO3S
Molar mass 100.06 g·mol−1
Appearance Colorless liquid
Density 1.84 g cm−3
Melting point −87.5 °C; −125.4 °F; 185.7 K
Boiling point 165.4 °C; 329.6 °F; 438.5 K
Acidity (pKa) -10
Basicity (pKb) 24
Structure
Tetragonal at S
Tetrahedral at S
Hazards
Safety data sheet ICSC 0996
Xn C
R-phrases R20, R35
S-phrases (S1/2), S26, S45
Related compounds
Related compounds
Antimony pentafluoride
Trifluoromethanesulfonic acid
Hydrofluoric acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Fluorosulfuric acid (IUPAC name: sulfurofluoridic acid) is the inorganic compound with the chemical formula HSO3F. It is one of the strongest acids commercially available. The formula HSO3F emphasizes its relationship to sulfuric acid, H2SO4; HSO3F is a tetrahedral molecule. It is a colourless liquid although commercial samples are often yellow.[1]

Chemical properties

Fluorosulfuric acid is a free-flowing colorless liquid. It is soluble in polar organic solvents (e.g. nitrobenzene, acetic acid, and ethyl acetate), but poorly soluble in nonpolar solvents such as alkanes. Reflecting its strong acidity, it dissolves almost all organic compounds that are even weak proton acceptors.[2] HSO3F hydrolyzes slowly to HF and sulfuric acid. The related triflic acid (CF3SO3H) retains the high acidity of HSO3F but is more hydrolytically stable. The self-ionization of fluorosulfonic acid also occurs:

2 HSO3F [H2SO3F]+ + [SO3F]           K = 4.0 × 10−8 (at 298 K)

Production

Fluorosulfuric acid is prepared by the reaction of HF and sulfur trioxide:[1]

SO3 + HF → HSO3F

Alternatively, KHF2 or CaF2 can be treated with oleum at 250 °C. Once freed from HF by sweeping with an inert gas, HSO3F can be distilled in a glass apparatus.[3]

Super-acids

HSO3F is one of the strongest known simple Brønsted acids, although carborane-based acids are still stronger.[4] It has an H0 value of −15.1 compared to 12 for sulfuric acid. The combination of HSO3F and the Lewis acid antimony pentafluoride produces "Magic acid", which is a far stronger protonating agent. These acids all fall into the category of "superacids", acids stronger than 100% sulfuric acid.

Applications

HSO3F is useful for regenerating mixtures of HF and H2SO4 for etching lead glass.

HSO3F isomerizes alkanes and the alkylation of hydrocarbons with alkenes,[5] although it is unclear if such applications are of commercial importance. It can also be used as a laboratory fluorinating agent.[3]

Safety

Fluorosulfuric acid is considered to be highly toxic and corrosive. It hydrolyzes to release HF. Addition of water to HSO3F can be violent, similar to the addition of water to sulfuric acid but much more violent.

See also

References

  1. 1 2 Erhardt Tabel, Eberhard Zirngiebl, Joachim Maas "Fluorosulfuric Acid" in "Ullmann's Encyclopedia of Industrial Chemistry" 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a11_431
  2. Olah, G. A.; Prakash, G. K.; Wang, Q.; Li, X.-Y. (2001). "Fluorosulfuric Acid". Encyclopedia of Reagents for Synthesis. John Wiley & Sons. doi:10.1002/047084289X.rf014.
  3. 1 2 Cotton, F. A.; Wilkinson, G. (1980). Advanced Inorganic Chemistry (4th ed.). New York: Wiley. p. 246. ISBN 0-471-02775-8.
  4. Christopher A. Reed "Myths about the Proton. The Nature of H+ in Condensed Media" Acc. Chem. Res., 2013, 46 (11), pp 2567–2575. doi:10.1021/ar400064q
  5. Olah, G.; Farooq, O.; Husain, A.; Ding, N.; Trivedi, N.; Olah, J. (1991). "Superacid HSO3F/HF-Catalyzed Butane Isomerisation". Catalysis Letters 10 (3–4): 239–247. doi:10.1007/BF00772077.
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