Superacid

A superacid is an acid with an acidity greater than that of 100% sulfuric acid. Some simple superacids include trifluoromethanesulfonic acid (CF₃SO₃H), also known as triflic acid, and fluorosulfuric acid (FSO₃H), both of which are about a thousand times stronger than sulfuric acid. In many cases, the superacid is not a single compound, but is instead a system of several compounds that are combined to effect high acidity.

The term superacid was originally coined by James Bryant Conant in 1927 in classifying acids that were stronger than conventional mineral acids. George Andrew Olah won the 1994 Nobel prize in chemistry for his investigations of superacids and their use in the direct observation of carbocations.

Olah's "magic acid" was named for its amazing ability to dissolve candle wax. Magic acid is a mix of the Lewis acid antimony pentafluoride (SbF₅) and fluorosulfuric acid (a Brønsted acid). The strongest known superacid system, called fluoroantimonic acid, is a mixture of hydrofluoric acid and antimony pentafluoride. In this system, hydrofluoric acid releases the proton (H⁺), and the conjugate base (F^-) is effectively sequestered by forming a strong coordinate bond with the fluorophilic antimony pentafluoride. The result of this coordinated bond is a large octahedral anion (SbF6^-), which is a very weak nucleophile and a very weak base. The proton effectively becomes a "free proton", which accounts for the system's extreme acidity. Fluoroantimonic acid is 2×10¹⁹ times stronger than 100% sulfuric acid.

See also

*Superbase