| Fluorosulfuric acid | |
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Sulfurofluoridic acid |
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Fluorusulfuric acid |
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Other names
Fluorosulfonic acid |
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| Identifiers | |
| CAS number | 7789-21-1 |
| PubChem | 24603 |
| ChemSpider | 23005 |
| EC number | 232-149-4 |
| UN number | 1777 |
| MeSH | Fluorosulfonic+acid |
| RTECS number | LP0715000 |
| Jmol-3D images | Image 1 Image 2 |
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| Properties | |
| Molecular formula | HFO3S |
| Molar mass | 100.07 g mol−1 |
| Exact mass | 99.963042793 g mol-1 |
| Appearance | Colorless liquid |
| Density | 1.84 g cm-3 |
| Melting point |
185.7 K |
| Boiling point |
438.5 K |
| Acidity (pKa) | -10 |
| Basicity (pKb) | 24 |
| Structure | |
| Coordination geometry |
Tetragonal at S |
| Molecular shape | Tetrahedral at S |
| Hazards | |
| MSDS | ICSC 0996 |
| EU Index | 016-018-00-7 |
| EU classification | Xn C |
| R-phrases | R20, R35 |
| S-phrases | (S1/2), S26, S45 |
| Related compounds | |
| Related compounds | Antimony pentafluoride Trifluoromethanesulfonic acid Hydrofluoric acid |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Fluorosulfuric acid (IUPAC name: sulfurofluoridic acid) is the inorganic compound with the formula HSO3F. It is one of the strongest acids commercially available and is a superacid. The formula HFSO3 emphasizes its relationship to sulfuric acid, H2SO4; HSO3F is a tetrahedral molecule.
Contents |
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 more hydrolytically stable. The self ionization of fluorosulfonic acid also occurs:
Fluorosulfuric acid is prepared by the reaction of HF and sulfur trioxide:
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]
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.
FSO3H is useful for regenerating mixtures of HF and H2SO4 for etching lead glass.
FSO3H isomerizes alkanes and the alkylation of hydrocarbons with alkenes,[4] although it is unclear if such applications are of commercial importance. It can also be used as a laboratory fluorinating agent.[2]
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. Addition of fluorosulfuric acid to water is much more violent process than addition of sulfuric acid.
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