In chemistry, a superbase is an extremely strong base. There is no commonly accepted definition for what qualifies as a superbase, but most chemists would accept sodium hydroxide as a 'benchmark' base just as sulfuric acid is a '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 are neutralized by water acting as an acid, to produce a corresponding 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.

Organometallic compounds of reactive metals are usually superbases, for example organolithium and organomagnesiums (Grignard reagents). Another type of organic superbase has a reactive metal exchanged for a hydrogen on a heteroatom, such as oxygen (unstabilized alkoxides) or nitrogen (lithium diisopropylamide).

Reactions involving superbases are usually water-sensitive, conducted under an inert atmosphere and at a low temperature. A desirable property in many cases is low nucleophilic reactivity, i.e. a non-nucleophilic base. Unhindered alkyllithiums, for example, cannot be used with electrophiles such as carbonyl groups, because they attack the electrophiles as nucleophiles.

In organic synthesis, the Schlosser base (or Lochmann-Schlosser base), i.e. the combination of "tert"-butyllithium and potassium tert-butoxide, is a commonly used superbase. "tert"-Butyllithium undergoes a cation exchange with potassium tert-butoxide giving tert-butyl potassium and lithium tert-butoxide, an exchange driven by lithium's affinity for the alkoxide oxygen. Replacement of the lithium cation with potassium causes the tert-butyl anion to acquire greater ionic character and thus greater basicity.

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 acids, like the aqueous hydronium ion. Alkali and earth alkali metal hydrides (sodium hydride, calcium hydride) are superbases.

ee also


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Superbase — In der Chemie ist eine Superbase eine extrem starke Base. Wie stark eine Base sein muss, um als „Superbase“ zu gelten, ist nicht eindeutig definiert  häufig wird Natriumhydroxid als Maßstab verwendet (demnach wäre eine Superbase also eine Base,… …   Deutsch Wikipedia

  • Superbase — Una superbase, en química, es una base extremadamente fuerte. No hay un estándar comúnmente aceptado para definir la base más fuerte, pero en general muchos químicos consideran al hidróxido de sodio como la base fuerte de referencia, así como al… …   Wikipedia Español

  • Superbase — Une superbase est un composé très basique. Bien qu il n y ait pas de limite de référence, on considère généralement qu une superbase est plus basique que la soude et peut donc donner une solution avec un pH supérieur à 14. Voir aussi Superacide… …   Wikipédia en Français

  • superbase — noun any compound having a very high basicity …   Wiktionary

  • Superbase — Su|per|ba|se: Bez. für Verb. bes. hoher Basizität, z. B. Kalium tert butylat, Protonenschwämme, Lithiumdiisopropylamin. – Ggs.: Supersäure …   Universal-Lexikon

  • Superbase database — Superbase is an end user desktop database program that started on the Commodore PET and was ported from that to various operating systems over the course of more than 20 years. It also has generally included a programming language to automate… …   Wikipedia

  • Decimal superbase — Many numeral systems with base 10 use a superimposed larger base of 100, 1000, 10000 or 1000000. It is a power of 10 and might be called a superbase or superradix of the numeral system. The superbase is mainly used in the spoken/written language… …   Wikipedia

  • Osprey Publishing — Ltd Repères historiques Création 1968 Fiche d’identité …   Wikipédia en Français

  • Liste der Dateiendungen/S — In dieser Liste sind übliche Dateinamenserweiterungen aufgelistet, die in einigen Betriebssystemen (wie zum Beispiel Microsoft Windows) zur Unterscheidung von Dateiformaten verwendet werden. In anderen Betriebssystemen erfolgt die… …   Deutsch Wikipedia

  • Superbasen — In der Chemie ist eine Superbase eine extrem starke Base. Wie stark eine Base sein muss, um als „Superbase“ zu gelten, ist nicht eindeutig definiert  häufig wird Natriumhydroxid als Maßstab verwendet (demnach wäre eine Superbase also eine… …   Deutsch Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.