Fluorosulfonic 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
3D model (Jmol)	Interactive image Interactive image
ChemSpider	23005 Y
ECHA InfoCard	100.029.227
EC Number	232-149-4
MeSH	Fluorosulfonic+acid
PubChem CID	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	1.726 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
Hazards
Safety data sheet	ICSC 0996
EU classification (DSD)	Xn C
R-phrases	R20, R35
S-phrases	(S1/2), S26, S45
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  (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.

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:

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, HSO₃F can be distilled in a glass apparatus.

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.