Fluorosulfuric acid

Names
IUPAC name Sulfurofluoridic acid
Systematic IUPAC name Fluorosulfuric acid[citation needed]
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 (JSmol)	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
UNII	PPX0648643 Y
UN number	1777
CompTox Dashboard (EPA)	DTXSID3033511
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
Conjugate base	Fluorosulfate
Structure
Coordination geometry	Tetragonal at S
Molecular shape	Tetrahedral at S
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H314, H332[1]
Precautionary statements	P261, P271, P280, P303+P361+P353, P304+P340+P310, P305+P351+P338[1]
NFPA 704 (fire diamond)	4 0 3 W OX
Safety data sheet (SDS)	ICSC 0996
Related compounds
Related compounds	Antimony pentafluoride Trifluoromethanesulfonic acid Hydrofluoric acid Sulfurous acid Sulfuric acid Sulfur hexafluoride
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. It is a tetrahedral molecule and is closely related to sulfuric acid, H₂SO₄, substituting a fluorine atom for one of the hydroxyl groups. It is a colourless liquid, although commercial samples are often yellow.^[2]

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.

HSO₃F is one of the strongest known simple Brønsted acids.^[3] 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 are categorized as "superacids", acids stronger than 100% sulfuric acid.

Reflecting its strong acidity, HSO₃F dissolves almost all organic compounds that are even weak proton acceptors.^[4] HSO₃F hydrolyzes slowly to hydrogen fluoride (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:

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

HSO₃F isomerizes alkanes and catalyzes the alkylation of hydrocarbons with alkenes,^[5] although it is unclear if such applications are of commercial importance. It can also be used as a laboratory fluorinating agent.^[6]

Production

Fluorosulfuric acid is prepared by the reaction of HF and sulfur trioxide:^[2]

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.^[6]

Safety

Fluorosulfuric acid is considered to be highly toxic and extremely 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.