Superbases

In chemistry, a superbase is an extremely basic compound or substance that has a high affinity for protons. The hydroxide ion is the strongest base possible in aqueous solutions, but bases that exist with much greater strengths than the bases that could exist in aqueous solutions are possible. Such bases are valuable in organic synthesis and are fundamental to physical organic chemistry. Superbases have been described and used since the 1850s. Reactions involving superbases often require special techniques since they are destroyed by water and atmospheric carbon dioxide as well as oxygen. Inert atmosphere techniques and low temperatures minimize these side reactions.

Superbase is defined as an organic compound whose basicity is greater than that of proton sponge, which has a pKa. Strong superbases can be prepared from extending the hydrogen bond network of multiple amino groups substituted on an aromatic core. Superbases are of great interest to practicing organic chemists due to their reactivity as well as good solubility in organic solvents. Superbases are also important environmentally as they have recently been found to participate in CO₂ fixation.

IUPAC defines superbases simply as a "compound having a very high basicity, such as lithium diisopropylamide." Caubère defines superbases qualitatively but more precisely: "The term superbases should only be applied to bases resulting from a mixing of two (or more) bases leading to new basic species possessing inherent new properties. The term superbase does not mean a base is thermodynamically and/or kinetically stronger than another, instead it means that a basic reagent is created by combining the characteristics of several different bases."

Superbases have also been defined semi-quantitatively as any species with a higher absolute proton affinity (APA = 245.3 kcal/mol) and intrinsic gas phase basicity (GB = 239 kcal/mol) than Alder's canonical proton sponge (1,8-bis-(dimethylamino)-naphthalene).

Three main classes of superbases are recognized: organic, organometallic and inorganic.

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