Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/11/17 00:34:40」(JST)

wiki en

In organic chemistry, transesterification is the process of exchanging the organic 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. The reaction can also be accomplished with the help of enzymes (biocatalysts) particularly lipases (E.C.3.1.1.3).

Transesterification: alcohol + ester → different alcohol + different ester

Strong acids catalyse the reaction by donating a proton to the carbonyl group, thus making it a more potent electrophile, whereas bases catalyse the reaction by removing a proton from the alcohol, thus making it more nucleophilic. 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 and evaporating the small alcohol to drive equilibrium.

Mechanism

In the transesterification mechanism, the carbonyl carbon of the starting ester (RCOOR¹) undergoes nucleophilic attack by the incoming alkoxide (R²O⁻) to give a tetrahedral intermediate, which either reverts 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.

Applications

Polyester production

The largest scale application of transesterification is in the synthesis of polyesters.^[1] 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 (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 U.S. 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 glycerine, which was used to produce explosives for World War II. Many of the methods used today by producers and homebrewers 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.

High-pressure transesterification

Base-catalyzed transesterification is characterized by a negative activation volume (approx. -12 cm³) and therefore it proceeds faster under high-pressure conditions. It has been shown that amine-catalyzed alcoholysis of sterically hindered esters (e.g. protecting groups, chiral auxiliaries) proceeds rapidly at room temperature under 10 kbar pressure, giving quantitative yields.^[2]

References

^ 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
^ Romanski, J.; Nowak, P.; Kosinski, K.; Jurczak, J. (Sep 2012). "High-pressure transesterification of sterically hindered esters". Tetrahedron Lett. 53 (39): 5287–5289. doi:10.1016/j.tetlet.2012.07.094.

UpToDate Contents

全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.

1. 血清ビリルビン定量の臨床的側面 clinical aspects of serum bilirubin determination

English Journal

Trifunctional Metal Ion-Catalyzed Solvolysis: Cu(II)-Promoted Methanolysis of N,N-bis(2-picolyl) Benzamides Involves Unusual Lewis Acid Activation of Substrate, Delivery of Coordinated Nucleophile, Powerful Assistance of the Leaving Group Departure.

Raycroft MA, Maxwell CI, Oldham RA, Andrea AS, Neverov AA, Brown RS.SourceDepartment of Chemistry, Queen's University , Kingston, Ontario, Canada K7L 3N6.
Inorganic chemistry.Inorg Chem.2012 Sep 12. [Epub ahead of print]
PMID 22971051

Biochemical studies on sphingolipids of Artemia franciscana: complex neutral glycosphingolipids.

Kojima H, Tohsato Y, Kabayama K, Itonori S, Ito M.SourceInstitute of Glycoscience, Tokai University, 4-1-1 Kitakaname, Hiratsuka, Kanagawa, 259-1292, Japan.
Glycoconjugate journal.Glycoconj J.2012 Aug 14. [Epub ahead of print]
Brine shrimp are primitive crustacean arthropodal model organisms, second to daphnia, which can survive in high-salinity environments. Their oviposited cysts, cuticle-covered diapausing eggs, are highly resistant to dryness. To elucidate specialties of brine shrimp, this study characterized glycosph
PMID 22890904

Japanese Journal

亜臨界または超臨界二酸化炭素中でのポリウレアのメタノールを用いた分解反応

本九町卓,向井真吾,古川睦久 [他]
日本ゴム協会誌 85(5), 157-161, 2012-05
NAID 40019254252

H_2SO_4/CaO-Catalyzed Process for Biodiesel Production from High Acid Value Jatropha curcas Crude Oil

TSUCHIYA Yooko,KANEKI Yuichi,YAMAKOSHI Yukiyasu
Journal of chemical engineering of Japan 44(4), 529-533, 2011-07-01
… A two-step H2SO4/CaO-catalyzed methanolysis process was used for the efficient conversion of Jatropha curcas crude oil, which has an acid value greater than 30 mg KOH/g, into fatty acid methyl ester (FAME). … Using this two-step methanolysis reaction, a FAME level greater than 96% could be obtained in the final product. …
NAID 10029241269