Fluorosulfuric acid

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Fluorosulfuric acid

Fluorosulfuric acid is FSO₃H; it is one of the strongest acids commercially available. It is also known by the alternative name, fluorosulfonic acid. The molecule is better described by the formula FSO₂OH, which emphasizes its relationship to sulfuric acid

Sulfuric acid

Sulfuric acid, hydrogen2sulfuroxygen4, is a strong mineral acid. It is soluble in water at all concentrations. Sulfuric acid has many applications, and is one of the top products of the chemical industry....
, H₂SO₄. FSO₃H is a tetrahedral molecule.

rosulfuric acid is a free-flowing colorless liquid.

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Encyclopedia

Sulfuric acid

Chemical properties

Fluorosulfuric acid is a free-flowing colorless liquid. It is soluble in polar organic solvents (e.g. nitrobenzene

Nitrobenzene

Nitrobenzene, also known as nitrobenzol or oil of mirbane, is an organic compound with the chemical formula Carbon6Hydrogen5NitrogenOxygen2....
, acetic acid

Acetic acid

Acetic acid, CH3COOH, also known as ethanoic acid, is an organic acid which gives vinegar its sour taste and pungent smell. Pure, water-free acetic acid is a colourless liquid that absorbs water from the environment , and freezes at 16.7 Celsius to a colourless crystalline solid....
, and ethyl acetate

Ethyl acetate

Ethyl acetate is the organic compound with the formula CH3COOCH2CH3. This colorless liquid has a characteristic sweet smell like certain glues or nail polish removers, in which it is used....
), 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. FSO₃H hydrolyze

Hydrolysis

Hydrolysis is a chemical reaction during which one or more water are split into hydrogen and hydroxide ions which may go on to participate in further reactions....
s slowly to HF and sulfuric acid

Sulfuric acid

Sulfuric acid, hydrogen2sulfuroxygen4, is a strong mineral acid. It is soluble in water at all concentrations. Sulfuric acid has many applications, and is one of the top products of the chemical industry....
. The related triflic acid CF₃SO₃H retains the high acidity of FSO₃H but is hydrolytically stable.

Production

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

Sulfur trioxide

Sulfur trioxide is the chemical compound with the formula SO3. In the gaseous form, this species is a significant pollutant, being the primary agent in acid rain....
SO₃ + HF ? FSO₃H Alternatively, KHF₂ or CaF₂ can be treated with oleum

Oleum

Oleum , or fuming sulfuric acid refers to a solution of various compositions of sulfur trioxide in sulfuric acid or sometimes more specifically to disulfuric acid ....
at 250 °C. Once freed from HF by sweeping with an inert gas, FSO₃H can be distilled in a glass apparatus.

Super-acids

FSO₃H is one of the strongest known simple Brønsted acids, although recent work on carborane

Carborane

A carborane is a cluster composed of boron and carbon atoms. Like many of the related boranes, these clusters are polyhedra and are similarly classified as closo-, nido-, arachno-, hypho-, etc....
-based acids have led to still stronger acids. It has an H₀ value of −15.1 compared to −12 for sulfuric acid. The combination of FSO₃H and the Lewis acid

Lewis acid

A Lewis acid is a chemical compound, A, that can accept a pair of electrons from a Lewis base, B, that acts as an electron-pair donor, forming an adduct, AB.Gilbert N....
antimony pentafluoride

Antimony pentafluoride

Antimony pentafluoride is the chemical compound with the formula AntimonyFluorine5. This colourless, viscous liquid is a valuable Lewis acid and a component of the superacid fluoroantimonic acid, the strongest known acid....
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

FSO₃H isomerizes alkanes and the alkylation of hydrocarbons with alkenes. 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 FSO₃H can be violent, similar to the addition of water to sulfuric acid.