Editing Transesterification

{{short description|Chemical reaction which exchanges the R groups of an alcohol and ester}}
{{Use dmy dates|date=September 2022}}

'''Transesterification''' is the process of exchanging the organic [[functional group]] R″ of an [[esters|ester]] with the organic group R' of an [[alcohols|alcohol]]. These reactions are often [[catalyst|catalyzed]] by the addition of an [[acid]] or [[base (chemistry)|base]] catalyst.<ref>{{cite journal|last1=Otera|first1=Junzo.|title=Transesterification|journal=Chemical Reviews|date=June 1993|volume=93|issue=4|pages=1449–1470|doi=10.1021/cr00020a004}}</ref> Strong acids catalyze the reaction by donating a [[proton]] to the [[carbonyl]] group, thus making it a more potent [[electrophile]]. Bases catalyze the reaction by removing a proton from the alcohol, thus making it more [[nucleophile|nucleophilic]]. The reaction can also be accomplished with the help of enzymes, particularly [[lipase]]s (one example is the lipase E.C.3.1.1.3<ref>{{Cite web|title=ENZYME – 3.1.1.3 Triacylglycerol lipase|url=https://enzyme.expasy.org/EC/3.1.1.3|access-date=2021-02-17|website=enzyme.expasy.org|publisher=[[Swiss Institute of Bioinformatics|SIB Swiss Institute of Bioinformatics]]}}</ref>).

[[Image:Transesterification.png|center|thumb|500px|{{center|'''Transesterification''': alcohol + ester → different alcohol + different ester}}]]

If the alcohol produced by the reaction can be separated from the reactants by distillation this will drive the [[Chemical equilibrium|equilibrium]] toward the products. This means that esters with larger [[alkoxy group]]s can be made from methyl or ethyl esters in high purity by heating the mixture of ester, acid/base, and large alcohol.

==Mechanism==
In the transesterification mechanism, the carbonyl carbon of the starting ester reacts to give a [[Tetrahedral molecular geometry|tetrahedral]] intermediate, which either reverts back to the starting material, or proceeds to the transesterified product (RCOOR<sup>2</sup>). The various species exist in equilibrium, and the product distribution depends on the relative energies of the reactant and product. Depending on reaction conditions [[ester hydrolysis]] and/or [[esterification]] will also occur, which results in some amount of free carboxylic acid being present.

:[[File:General transesterification mechanism.png|500px]]

==Applications==
===Polyester production===
The largest scale application of transesterification is in the synthesis of [[polyester]]s.<ref name=Ullmann>Wilhelm Riemenschneider1 and Hermann M. Bolt "Esters, Organic" Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. {{doi|10.1002/14356007.a09_565.pub2}}</ref> In this application, diesters undergo transesterification with diols to form macromolecules. For example, [[dimethyl terephthalate]] and [[ethylene glycol]] react to form [[polyethylene terephthalate]] and [[methanol]], which is evaporated to drive the reaction forward.

===Methanolysis and biodiesel production===
The reverse reaction, methanolysis, is also an example of transesterification. This process has been used to recycle polyesters into individual monomers (see [[plastic recycling]]). It is also used to convert fats ([[triglyceride]]s) into [[biodiesel]]. This conversion was one of the first uses. Transesterified [[vegetable oil]] ([[biodiesel]]) was used to power heavy-duty vehicles in South Africa before [[World War II]].

It was [[patented]] in the US in the 1950s by [[Colgate-Palmolive|Colgate]], though [[biolipid]] transesterification may have been discovered much earlier. In the 1940s, researchers were looking for a method to more readily produce [[glycerol]], which was used to produce [[explosives]] for World War II. Many of the methods used today by producers have their origin in the original 1940s research.

Biolipid transesterification has also been recently shown by Japanese researchers to be possible using a [[Supercritical fluid|supercritical]] methanol methodology, whereby high temperature, high-pressure vessels are used to physically catalyze the biolipid/methanol reaction into fatty-acid methyl esters.<ref>{{Cite journal |last=Ehimen |first=E. A. |last2=Sun |first2=Z. F. |last3=Carrington |first3=C. G. |date=2010-03-01 |title=Variables affecting the in situ transesterification of microalgae lipids |url=https://www.sciencedirect.com/science/article/pii/S0016236109004736 |journal=Fuel |volume=89 |issue=3 |pages=677–684 |doi=10.1016/j.fuel.2009.10.011 |issn=0016-2361|url-access=subscription }}</ref>

===Fat processing===
[[Fat interesterification]] is used in the [[food industry]] to rearrange the [[fatty acid]]s of [[triglyceride]]s in edible [[fat]]s and [[vegetable oil]]s. For example, a solid fat with mostly saturated fatty acids may be transesterified with a vegetable oil having high unsaturated acid contents, to produce a spreadable semisolid fat whose molecules have a mix both kinds of acids.

===Synthesis===
Transesterification is used to synthesize [[enol]] derivatives, which are difficult to prepare by other means. [[Vinyl acetate]], which is cheaply available, undergoes transesterification, giving access to [[enol ether|vinyl ether]]s:<ref>{{cite journal|title=Iridium-catalyzed Synthesis of Vinyl Ethers from Alcohols and Vinyl Acetate|author=Tomotaka Hirabayashi |author2=Satoshi Sakaguchi |author3=Yasutaka Ishii |journal=Org. Synth.|year=2005|volume=82|page=55|doi=10.15227/orgsyn.082.0055|doi-access=free}}</ref><ref name=Ishii>{{cite journal|title=Discussion Addendum: Iridium-catalyzed Synthesis of Vinyl Ethers from Alcohols and Vinyl Acetate|author=Yasushi Obora |author2=Yasutaka Ishii |journal=Org. Synth.|year=2012|volume=89|page=307|doi=10.15227/orgsyn.089.0307}}</ref>
: ROH + {{chem|AcOCH{{=}}CH|2}} ⟶ {{chem|ROCH{{=}}CH|2}} + AcOH
The reaction can be effected with high enantioselectivity when mediated with a [[lipase]].<ref>{{cite book |doi=10.1002/047084289X.rv008|chapter=Vinyl Acetate |title=Encyclopedia of Reagents for Organic Synthesis |year=2001 |last1=Manchand |first1=Percy S. |isbn=0-471-93623-5 }}</ref>

==See also==
*[[Biodiesel production]]
*[[Otera's catalyst]]
*[[Transalkylation]]
*[[Transamidification]]
*[[Cocaethylene]]

==References==
{{reflist}}

{{Alcohols}}
{{Authority control}}

[[Category:Lipid methods]]
[[Category:Reactions of esters]]
[[Category:Substitution reactions]]