Fluorosulfuric acid
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| Fluorosulfuric acid | |
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| Other names | Fluorosulfonic acid, Fluorosulfuric acid, |
| Identifiers | |
| CAS number | [7789-21-1] |
| EINECS number | |
| RTECS number | LP0715000 |
| Properties | |
| Molecular formula | FSO3H. |
| Molar mass | 100.0645 g/mol |
| Appearance | Colorless liquid |
| Density | 1.84 g/cm-3, liquid |
| Melting point |
-87.3 °C |
| Boiling point |
165.5 °C |
| Solubility in water | Soluble |
| Acidity (pKa) | -10 |
| Structure | |
| Molecular shape | tetrahedral |
| Dipole moment | N/A |
| Hazards | |
| EU classification | 1777 Corrosive material |
| R-phrases | 20-35 |
| S-phrases | 26-45 |
| Related compounds | |
| Related compounds | Antimony pentafluoride Trifluoromethanesulfonic acid HF |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
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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.
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[edit] 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.[1] FSO3H hydrolyzes slowly to HF and sulfuric acid. The related triflic acid CF3SO3H retains the high acidity of FSO3H but is hydrolytically stable.
[edit] Production
Fluorosulfuric acid is prepared by the reaction of HF and sulfur trioxide
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- SO3 + HF → FSO3H
Alternatively, 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.[2]
[edit] 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.[3] 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. These acids all fall into the category of "superacids", acids stronger than 100% sulfuric acid.
[edit] Applications
FSO3H isomerizes alkanes and the alkylation of hydrocarbons with alkenes.[4] It can also be used as a laboratory fluorinating agent.[2]
[edit] 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.
[edit] References
- ^ Encyclopedia of Reagents for Organic Synthesis 2001 John Wiley & Sons, Ltd
- ^ a b Cotton, F.A.; Wilkinson, G. (1980) Advanced Inorganic Chemistry: A Comprehensive Text, 4th Edition, p.246, Wiley-Interscience Publications.
- ^ M. Juhasz, S. Hoffmann, E. Stoyanov, K.-C. Kim, C. A. Reed, Angewandte Chemie International Edition 43 5352 - 5355 2004.
- ^ Olah, G.; Farooq, O.; Husain, A.; Ding, N.; Trivedi, N.; Olah, J. (1991) Superacid FSO3H/HF-Catalyzed Butane Isomerisation. Catalysis Letters 10, 239-248.
