Fluorosulfuric acid

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Fluorosulfuric acid
IUPAC name
Sulfurofluoridic acid
Other names
Epoxysulfonyl fluoride
Fluoridosulfonic acid
Fluoridosulphonic acid
Fluorinesulfonic acid
Fluorinesulphonic acid
Fluorosulfonic acid
Fluorosulphonic acid
Monofluorosulfuric acid
Sulfuric fluorohydrin
Molar mass 100.06 g/mol
Appearance Colorless liquid
Odor Pungent
Density 1.726 g/cm3
Melting point −87.5 °C (−125.5 °F; 185.7 K)
Boiling point 165.4 °C (329.7 °F; 438.5 K)
Solubility Reacts with amines
Soluble in glacial acetic acid, ethyl acetate, nitrobenzene
Poorly soluble in alkanes
Vapor pressure 2.47 mmHg at 25 °C
Acidity (pKa) -10
Safety data sheet Sigma-Aldrich
Flash point Non-flammable
Related compounds
Related compounds
Sulfuric acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Fluorosulfuric acid or sulfurofluoridic acid is one of the strongest commercially available acids, more specifically a superacid. It has the chemical formula HFSO3.



Fluorosulfuric 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.

Fluorosulfuric acid reacts with water to release sulfuric acid and hydrofluoric acid.


Fluorosulfuric acid is a colorless liquid that fumes in air and reacts violently with water.


Fluorosulfuric acid is sold by chemical suppliers, though it's not easy to acquire.


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

HF + SO3 → HSO3F

Alternatively, KHF2 or CaF2 can be treated with oleum at 250 °C. After the HF is removed by sweeping with an inert gas, HSO3F can be distilled in a glass apparatus.


  • Make magic acid



Fluorosulfuric acid is considered to be highly toxic and corrosive. It hydrolyzes to release HF. Addition of water to this acid is extremely violent, much more that the addition of water to concentrated sulfuric acid.

An antidote for HF, such as calcium gluconate should be present when handling this acid.


Fluorosulfuric acid should be kept in thick HDPE or PTFE bottles, in a dry place.


Strongly dilution with cold water, followed by careful neutralization with a base. Products are sulfates and fluorides, which can be dumped in trash.


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