Transesterification is the process of exchanging the organic functional group R″ of an ester with the organic group R' of an alcohol. These reactions are often catalyzed by the addition of an acid or base catalyst.[1] 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 nucleophilic. The reaction can also be accomplished with the help of other enzymes, particularly lipases (one example is the lipase E.C.3.1.1.3[2]).
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 equilibrium toward the products. This means that esters with larger alkoxy groups can be made from methyl or ethyl esters in high purity by heating the mixture of ester, acid/base, and large alcohol.
In the transesterification mechanism, the carbonyl carbon of the starting ester reacts to give a tetrahedral intermediate, which either reverts back to the starting material, or proceeds to the transesterified product (RCOOR2). 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.
Applicationsedit
Polyester productionedit
The largest scale application of transesterification is in the synthesis of polyesters.[3] 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 productionedit
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 (triglycerides) 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, 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 super-critical methanol methodology, whereby high temperature, high-pressure vessels are used to physically catalyze the biolipid/methanol reaction into fatty-acid methyl esters.[4]
Fat processingedit
Fat interesterification is used in the food industry to rearrange the fatty acids of triglycerides in edible fats and vegetable oils. 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.
Synthesisedit
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 vinyl ethers:[5][6]
ROH + AcOCH=CH 2 ⟶ ROCH=CH 2 + AcOH
The reaction can be effected with high enantioselectivity when mediated with a lipase.[7]
^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
^Ehimen, E. A.; Sun, Z. F.; Carrington, C. G. (1 March 2010). "Variables affecting the in situ transesterification of microalgae lipids". Fuel. 89 (3): 677–684. doi:10.1016/j.fuel.2009.10.011. ISSN 0016-2361.
^Tomotaka Hirabayashi; Satoshi Sakaguchi; Yasutaka Ishii (2005). "Iridium-catalyzed Synthesis of Vinyl Ethers from Alcohols and Vinyl Acetate". Org. Synth. 82: 55. doi:10.15227/orgsyn.082.0055.
^Yasushi Obora; Yasutaka Ishii (2012). "Discussion Addendum: Iridium-catalyzed Synthesis of Vinyl Ethers from Alcohols and Vinyl Acetate". Org. Synth. 89: 307. doi:10.15227/orgsyn.089.0307.
^Manchand, Percy S. (2001). "Vinyl Acetate". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rv008. ISBN0-471-93623-5.
December 08, 2023
transesterification, process, exchanging, organic, functional, group, ester, with, organic, group, alcohol, these, reactions, often, catalyzed, addition, acid, base, catalyst, strong, acids, catalyze, reaction, donating, proton, carbonyl, group, thus, making, . Transesterification is the process of exchanging the organic functional group R of an ester with the organic group R of an alcohol These reactions are often catalyzed by the addition of an acid or base catalyst 1 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 nucleophilic The reaction can also be accomplished with the help of other enzymes particularly lipases one example is the lipase E C 3 1 1 3 2 Transesterification alcohol ester different alcohol different esterIf the alcohol produced by the reaction can be separated from the reactants by distillation this will drive the equilibrium toward the products This means that esters with larger alkoxy groups can be made from methyl or ethyl esters in high purity by heating the mixture of ester acid base and large alcohol Contents 1 Mechanism 2 Applications 2 1 Polyester production 2 2 Methanolysis and biodiesel production 2 3 Fat processing 2 4 Synthesis 3 See also 4 ReferencesMechanism editIn the transesterification mechanism the carbonyl carbon of the starting ester reacts to give a tetrahedral intermediate which either reverts back to the starting material or proceeds to the transesterified product RCOOR2 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 nbsp Applications editPolyester production edit The largest scale application of transesterification is in the synthesis of polyesters 3 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 edit 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 triglycerides 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 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 super critical methanol methodology whereby high temperature high pressure vessels are used to physically catalyze the biolipid methanol reaction into fatty acid methyl esters 4 Fat processing edit Fat interesterification is used in the food industry to rearrange the fatty acids of triglycerides in edible fats and vegetable oils 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 edit 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 vinyl ethers 5 6 ROH AcOCH CH2 ROCH CH2 AcOHThe reaction can be effected with high enantioselectivity when mediated with a lipase 7 See also editBiodiesel production Otera s catalyst Transalkylation Transamidification CocaethyleneReferences edit Otera Junzo June 1993 Transesterification Chemical Reviews 93 4 1449 1470 doi 10 1021 cr00020a004 ENZYME 3 1 1 3 Triacylglycerol lipase enzyme expasy org SIB Swiss Institute of Bioinformatics Retrieved 17 February 2021 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 Ehimen E A Sun Z F Carrington C G 1 March 2010 Variables affecting the in situ transesterification of microalgae lipids Fuel 89 3 677 684 doi 10 1016 j fuel 2009 10 011 ISSN 0016 2361 Tomotaka Hirabayashi Satoshi Sakaguchi Yasutaka Ishii 2005 Iridium catalyzed Synthesis of Vinyl Ethers from Alcohols and Vinyl Acetate Org Synth 82 55 doi 10 15227 orgsyn 082 0055 Yasushi Obora Yasutaka Ishii 2012 Discussion Addendum Iridium catalyzed Synthesis of Vinyl Ethers from Alcohols and Vinyl Acetate Org Synth 89 307 doi 10 15227 orgsyn 089 0307 Manchand Percy S 2001 Vinyl Acetate Encyclopedia of Reagents for Organic Synthesis doi 10 1002 047084289X rv008 ISBN 0 471 93623 5 Retrieved from https en 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