Fluoroantimonic acid

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Fluoroantimonic acid

Fluoroantimonic acid HSbF₆ is a mixture of hydrogen fluoride

Hydrogen fluoride

Hydrogen fluoride is a chemical compound with the chemical formula HF. It is the principal industrial source of fluorine, often in the aqueous form as hydrofluoric acid, and thus is the precursor to many important compounds including pharmaceuticals and polymers ....
and 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....
in various ratios. The 1:1 combination affords the strongest known superacid

Superacid

A superacid is an acid with an acidity greater than that of 100% sulfuric acid, which has a Hammett acidity function of -12. Commercially available superacids include trifluoromethanesulfonic acid , also known as triflic acid, and fluorosulfuric acid , both of which are about a thousand times stronger than sulfuric acid....
, which has been demonstrated to protonate even hydrocarbon

Hydrocarbon

In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. With relation to chemical terminology, aromatic hydrocarbons or arenes, alkanes, alkenes and alkyne-based compounds composed entirely of carbon or hydrogen are referred to as "pure" hydrocarbons, whereas other hydrocarbons with bonded com...
s to afford carbocation

Carbocation

A carbocation is an ion with a positively-charged carbon atom. The charged carbon atom in a carbocation is a "sextet", i.e. it has only six electrons in its outer Electron shell#Valence shell instead of the eight valence electrons that ensures maximum stability ....
s and H₂.

The reaction of hydrogen fluoride (HF) and SbF₅ is exothermic. HF releases its proton (H⁺), and its conjugate base (F^-) is sequestered by one of more molecules SbF₅ to give the octahedral

Octahedron

An octahedron is a polyhedron with eight faces. A regular octahedron is a Platonic solid composed of eight equilateral triangles, four of which meet at each wikt:vertex....
SbF₆^-.

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Encyclopedia

Fluoroantimonic acid HSbF₆ is a mixture of hydrogen fluoride

Hydrogen fluoride

Antimony pentafluoride

Superacid

Hydrocarbon

Carbocation

Octahedron

An octahedron is a polyhedron with eight faces. A regular octahedron is a Platonic solid composed of eight equilateral triangles, four of which meet at each wikt:vertex....
SbF₆^-. This anion is classified as noncoordinating, because it is both a very weak nucleophile

Nucleophile

In chemistry, a nucleophile is a reagent that forms a chemical bond to its reaction partner by donating both bonding electrons. Because nucleophiles donate electrons, they are by definition Lewis bases ....
and a very weak base

Base (chemistry)

In chemistry, a base is most commonly thought of as an aqueous substance that can accept protons. A base is also often referred to as an alkali if OH- ions are involved....
. The proton

Proton

The proton is a subatomic particle with an electric charge of +1 elementary charge. It is found in the nucleus of each atom but is also stable by itself and has a second identity as the hydrogen ion, H+....
effectively becomes "naked", which accounts for the system's extreme acidity. Fluoroantimonic acid is 2×10¹⁹ (20 quintillion) times stronger than 100% 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 reaction of hydrofluoric acid and antimony pentafluoride proceeds as follows

Structure

Two related products have been crystallised from HF-SbF₅ mixtures, and both have been analyzed by single crystal X-ray crystallography

Crystallography

Crystallography is the experimental science of determining the arrangement of atoms in solids. In older usage, it is the scientific study of crystals....
. These salts have the formulas [H₂F⁺][Sb₂F₁₁^-] and [H₃F₂⁺][Sb₂F₁₁^-]. In both salts the anion is Sb₂F₁₁^-. As mentioned above, SbF₆^- is classified as weakly basic; the larger monoanion Sb₂F₁₁^- would be expected to be still weaker.

Comparison with other acids

The following values are based upon the Hammett acidity function

Hammett acidity function

The Hammett acidity function is a measure of acidity that is used for very concentrated solutions of strong acids, including superacids. In such solutions, simple approximations such as the Henderson-Hasselbalch equation are no longer valid due to the variations of the activity coefficients in highly concentrated solutions....
. Acidity is indicated by large negative values of H₀.

Fluoroantimonic acid (1990) (H₀ Value = -31.3)
Magic acid (1974) (H₀ Value = -19.2)
Carborane superacid (1969) (H₀ Value = -18.0)
Fluorosulfuric acid
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....
(1944) (H₀ Value = -15.1)
Triflic acid (1940) (H₀ Value = -14.9)

Applications

This extraordinarily strong acid protonates nearly all organic compound

Organic compound

An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered Inorganic compound....
s. In 1967, Bickel and Hogeveen showed that HF-SbF₅ will remove H₂ from isobutane

Isobutane

Isobutane, also known as methylpropane or 2-methylpropane, is an alkane, isomeric with butane. Recent concerns with depletion of the ozone layer by freon gases have led to increased use of isobutane as a gas for refrigeration systems, especially in domestic refrigerators and freezers, and as a propellant in aerosol sprays....
and methane from neopentane

Neopentane

Neopentane, also called dimethylpropane or 2,2-dimethylpropane, is a double-branched-chain alkane with five carbon atoms. Neopentane is an extremely flammable gas at room temperature and pressure which can condense into a highly Volatility liquid on a cold day, in an ice bath, or when compressed to a higher pressure....
: ₃CH + H⁺ ? (CH₃)₃C⁺ + H₂ ₄C + H⁺ ? (CH₃)₃C⁺ + CH₄

Safety

HF-SbF₅ is rapidly and explosively decomposed by water. It reacts with virtually all known solvents. Solvent

Solvent

A solvent is a liquid or gas that dissolves a solid, liquid, or gaseous solute, resulting in a solution.The most common solvent in everyday life is water....
s that have been proven to be compatible with HF-SbF₅ are SO₂ClF

Sulfuryl chloride fluoride

Sulfuryl chloride fluoride is the chemical compound with the formula SO2ClF. It is employed as a solvent for highly oxidizing compounds....
and liquified sulfur dioxide

Sulfur dioxide

Sulfur dioxide is the chemical compound with the formula SO2. It is produced by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide....
. Chlorofluorocarbons have also been used as solvents. Containers for HF-SbF₅ are made of PTFE

Polytetrafluoroethylene

In chemistry, poly or poly is a synthetic fluoropolymer which finds numerous applications. PTFE is most well known by the DuPont brand name Teflon....
.