Fluorosulfuric acid

Chembox new
Name = Fluorosulfuric acid
ImageFile = Fluorosulfuric-acid-2D.png ImageName = Fluorosulfuric acid
ImageFile1 = Fluorosulfuric-acid-3D-vdW.png ImageName1 = Fluorosulfuric acid
OtherNames = Fluorosulfonic acid,
Fluorosulfuric acid,

Section1 = Chembox Identifiers
CASNo = 7789-21-1
EINECS = 232-149-4
RTECS = LP0715000
Section2 = Chembox Properties
Formula = FSO₃H.
MolarMass = 100.0645 g/mol
Appearance = Colorless liquid
Density = 1.84 g/cm^-3, liquid
Solubility = Soluble
MeltingPt = -87.3 °C
BoilingPt = 165.5 °C
pKa = -10
Section3 = Chembox Structure
MolShape = tetrahedral
Dipole = N/A
Section7 = Chembox Hazards
ExternalMSDS =
EUClass = 1777 Corrosive material
RPhrases = 20-35
SPhrases = 26-45
Section8 = Chembox Related
OtherCpds = Antimony pentafluoride
Trifluoromethanesulfonic acid
HF

Fluorosulfuric acid is FSO₃H; it is one of the strongest acids commercially available. It is also known by the alternative name, fluorosulfonic acid. The molecule is better described by the formula FSO₂OH, which emphasizes its relationship to sulfuric acid, H₂SO₄. FSO₃H is a tetrahedral molecule.

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. [ Encyclopedia of Reagents for Organic Synthesis 2001 John Wiley & Sons, Ltd] FSO₃H hydrolyzes slowly to HF and sulfuric acid. The related triflic acid CF₃SO₃H retains the high acidity of FSO₃H but is hydrolytically stable.

Production

Fluorosulfuric acid is prepared by the reaction of HF and sulfur trioxide::SO₃ + HF → FSO₃HAlternatively, KHF₂ or CaF₂ can be treated with oleum at 250 °C. Once freed from HF by sweeping with an inert gas, FSO₃H can be distilled in a glass apparatus.Cotton, F.A.; Wilkinson, G. (1980) "Advanced Inorganic Chemistry: A Comprehensive Text", 4th Edition, p.246, Wiley-Interscience Publications.]

uper-acids

FSO₃H is one of the strongest known simple Brønsted acids, although recent work on carborane-based acids have led to still stronger acids. [M. Juhasz, S. Hoffmann, E. Stoyanov, K.-C. Kim, C. A. Reed, Angewandte Chemie International Edition 43 5352 - 5355 2004.] It has an "H"₀ value of −15.1 compared to −12 for sulfuric acid. The combination of FSO₃H 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

FSO₃H isomerizes alkanes and the alkylation of hydrocarbons with alkenes. [Olah, G.; Farooq, O.; Husain, A.; Ding, N.; Trivedi, N.; Olah, J. (1991) Superacid FSO₃H/HF-Catalyzed Butane Isomerisation. Catalysis Letters 10, 239-248.] It can also be used as a laboratory fluorinating agent.

afety

Fluorosulfuric acid is considered to be highly toxic and corrosive. It hydrolyzes to release HF. Addition of water to FSO₃H can be violent, similar to the addition of water to sulfuric acid.

References