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Superbase
From Wikipedia, the free encyclopedia
In chemistry, a superbase is an extremely strong base. There is no commonly accepted standard for "stronger than what?" although most chemists will happily consider sodium hydroxide as their 'benchmark' base just as they use sulfuric acid as their 'benchmark' acid (see superacid). The hydroxide ion is a good benchmark, because it is the strongest base that can exist in a water solution; stronger bases neutralize water as an acid by deprotonation, to produce hydroxide (and protonated superbase). Another use that can define superbase is stoichiometric α-deprotonation of a carbonyl compound into an enolate, something that cannot be done by "regular bases". Despite this, the term still doesn't have a standard chemical definition, so for example Proton Sponge may be called "superbase".
There are three main classes of superbases: organic, organometallic, and inorganic.
In organic synthesis, the Lochmann-Schlosser base, i.e. the combination of n-butyllithium and potassium tert-butoxide, is commonly referred to as a superbase. In this combination of reagents the tertiary alcoholate serves to complex the lithium ion, thus freeing the carbanion from its close association with the metal ion. Other such systems are collectively called harpoon bases.
Inorganic superbases are typically salts with highly charged, small negative ions, e.g. lithium nitride, which has extreme negative charge density and so is highly attracted to the aqueous hydronium ion.