Fluorosulfuric acid

Fluorosulfuric acid
Chemical structure of Fluorosulfuric acid
General
Other names	Fluorosulfonic acid, Fluorosulfuric acid,
Molecular formula	FSO3H.
Ho value	- 15.1
Molar mass	100.0645 g/mol
Appearance	Colorless, liquid.
CAS number	7789-21-1
EINECS number	N/A
Properties
Density and phase	1.84 g/cm-3, liquid
Solubility in water	Soluble
Solubility in other solvents	ether, alcohols.
Melting point	-87.3 °C
Boiling point	165.5 °C
Acidity (pKa)	-10
Structure
Molecular shape	tetrahedral
Dipole moment	N/A
Hazards
MSDS	External MSDS
EU classification	1777 Corrosive material
R-phrases	20-35
S-phrases	26-45
PEL (US, OSHA)	N/A
IDLH (US, NIOSH)	N/A
RTECS number	LP0715000
Supplementary data page
Structure & properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Related compounds
Related compounds	Antimony pentafluoride CF3SO3H HF
Except where noted otherwise, data are given for materials in their standard state (at 25°C, 100 kPa) Infobox disclaimer and references

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, SO₂(OH)₂. 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, diethyl ether, 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]. 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 â†' 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 [3].

Super-acids

FSO₃H is one of the strongest known simple Brønsted acids, although recent work on carborane-based acids have led to still stronger acids[1]. It has an H₀ 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.

Applications

FSO₃H isomerizes alkanes and the alkylation of hydrocarbons with alkenes [4]. 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 FSO₃H can be violent, similar to the addition of water to sulfuric acid.

References

[1]M. Juhasz, S. Hoffmann, E. Stoyanov, K.-C. Kim, C. A. Reed, Angewandte Chemie International Edition 43 5352 - 5355 2004.

[2] Encyclopedia of Reagents for Organic Synthesis 2001 John Wiley & Sons, Ltd

[3] Cotton, F.A.; Wilkinson, G. (1980) Advanced Inorganic Chemistry: A Comprehensive Text, 4th Edition, p.246, Wiley-Interscience Publications.

[4] Olah, G.; Farooq, O.; Husain, A.; Ding, N.; Trivedi, N.; Olah, J. (1991) Superacid FSO₃H/HF-Catalyzed Butane Isomerisation. Catalysis Letters 10, 239-248.

External links