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
CAS Number	7789-21-1 Y
ChemSpider	23005 Y
EC Number	232-149-4
Jmol 3D model	Interactive image Interactive image
MeSH	Fluorosulfonic+acid
PubChem	24603
RTECS number	LP0715000
UN number	1777
InChI InChI=1S/FHO3S/c1-5(2,3)4/h(H,2,3,4) Y Key: UQSQSQZYBQSBJZ-UHFFFAOYSA-N Y InChI=1/FHO3S/c1-5(2,3)4/h(H,2,3,4) Key: UQSQSQZYBQSBJZ-UHFFFAOYAW
SMILES OS(F)(=O)=O FS(=O)(=O)O
Properties
Chemical formula	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
Coordination geometry	Tetragonal at S
Molecular shape	Tetrahedral at S
Vapor pressure	{{{value}}}
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).
Y verify (what is YN ?)
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.

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. 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:

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

Production

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

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.

Super-acids

HSO₃F is one of the strongest known simple Brønsted acids, although carborane-based acids are still stronger. 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, although it is unclear if such applications are of commercial importance. It can also be used as a laboratory fluorinating agent.

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

• Chlorosulfuric acid
• Fluoroboric acid
• Fluoroantimonic acid
• Sulfuryl fluoride
• Methyl fluorosulfonate, an organic ester of FSO₃H
• Fluorosulfonylamine FSO₂NH₂, the formal acid amide