Editing Hydroxide (section)

===Base catalysis===
The hydroxide ion may act as a [[base catalyst]].<ref>{{cite book|editor-last1= Hattori |editor-first1=H.|editor-last2=Misono|editor-first2=M.|editor-last3=Ono|editor-first3=Y.|title=Acid–Base catalysis II|year=1994|publisher=Elsevier|isbn= 978-0-444-98655-9}}</ref> The base abstracts a proton from a weak acid to give an intermediate that goes on to react with another reagent. Common substrates for proton abstraction are [[Alcohol (chemistry)|alcohol]]s, [[phenol]]s, [[amine]]s, and [[carbon acid]]s. The [[acid dissociation constant|p''K''<sub>a</sub>]] value for dissociation of a C–H bond is extremely high, but the pK<sub>a</sub> [[alpha hydrogen]]s of a carbonyl compound are about 3 log units lower. Typical p''K''<sub>a</sub> values are 16.7 for [[acetaldehyde]] and 19 for [[acetone]].<ref>Ouellette, R.J. and Rawn, J.D. "Organic Chemistry" 1st Ed. Prentice-Hall, Inc., 1996: New Jersey. {{ISBN|0-02-390171-3}}.</ref> Dissociation can occur in the presence of a suitable base.
:RC(O)CH<sub>2</sub>R' + B {{eqm}} RC(O)CH<sup>−</sup>R' + BH<sup>+</sup>
The base should have a p''K''<sub>a</sub> value not less than about 4 log units smaller, or the equilibrium will lie almost completely to the left.

The hydroxide ion by itself is not a strong enough base, but it can be converted to one by adding sodium hydroxide to [[ethanol]]
:OH<sup>−</sup> + EtOH {{eqm}} EtO<sup>−</sup> + H<sub>2</sub>O
to produce the [[ethoxide]] ion. The [[acid dissociation constant|pK<sub>a</sub>]] for self-dissociation of ethanol is about 16, so the alkoxide ion is a strong enough base.<ref>{{cite book |title=Organic chemistry |url=https://archive.org/details/organicchemistry04pine |url-access=limited |last=Pine |first=S.H.
|author2=Hendrickson, J.B. |author3=Cram, D.J. |author4= Hammond, G.S. |year=1980 |publisher=McGraw–Hill |isbn=978-0-07-050115-7
|page=[https://archive.org/details/organicchemistry04pine/page/206 206]}}</ref> The addition of an alcohol to an [[aldehyde]] to form a [[hemiacetal]] is an example of a reaction that can be catalyzed by the presence of hydroxide. Hydroxide can also act as a Lewis-base catalyst.<ref>{{cite journal|journal=Angewandte Chemie International Edition |last=Denmark |first=S.E.|author2=Beutne, G.L. |year=2008 |title=Lewis Base Catalysis in Organic Synthesis |volume=47 |issue=9 |pages=1560–1638|doi=10.1002/anie.200604943|pmid=18236505 }}</ref>