Chem. Rev. 1993, 93. 1449-1470
1449
Transesterification Junzo Otera Department of Applied Chemistry, Okayama University of Science, Ridal-cho, Okayama 700, Japan Received October 26, 1992 (Revised Manuscript Received March
15, 1993)
Contents I. II. III. IV.
Introduction
Acid Catalysts Base Catalysts Amine Catalysts V. Equilibrium and Use of Molecular Sieves VI. Lewis Acid and Metal Alkoxide Catalysts VII. Titanium Tetraalkoxlde Catalysts
VIII.
Organotin Catalysts IX. Use of 2-Pyrldyl Esters X. Miscellaneous Methods under Mild Conditions XI. Macrolactonlzation XII. Enzymes A. General Features B. Resolution of Racemates C. Acylation of Polyol Derivatives D. Lactonizatlon and Poiycondensation XIII. Catalytic Antibody XIV. Concluding Remarks XV. References
1449 1450 1451 1452 1455 1455 1456 1457
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/, Introduction of the classic organic reactions that have enjoyed numerous laboratory uses and industrial applications. Organic chemists make use of this reaction quite often as a convenient means to prepared esters. On some occasions, transesterification is more advantageous than the ester synthesis from carboxylic acids and alcohols. For instance, some carboxylic acids are sparingly soluble in organic solvents Transesterification is
one
Junzo Otera received both a B.S. degree In 1966 and a Ph.D. degree In 1971 from Osaka University. He then became a research chemist at Central Research Laboratories of Kuraray Co. Ltd. He moved to Okayama University of Science as an associate professor in 1979 and has been a fuli professor since 1986. His research interests are synthetic applications of organometalllc and organosulfur compounds. For these achievements, he won the Chemical Society of Japan awards twice: technical development of organotin catalyst for polymerization of oxlranes, In 1985, and divisional award of Industrial organic chemistry for novel heteroatom chemistry, in 1991.
esterification of terephthalic acid today. Notably, undimished potential of the transesterification process even in the modern industry has been exemplified by a recent Chemical and Engineering News article: cosynthesis of ethylene glycol and dimethyl carbonate from ethylene carbonate and methanol (eq l).1 -O
S)
and accordingly difficult to subject to homogeneous esterification whereas esters are commonly soluble in most of organic solvents. The ester-to-ester transformation is particularly useful when the parent carboxylic acids are labile and difficult to isolate. Some esters, especially methyl and ethyl esters, are readily or commercially available and thus they serve conveniently
Mrf) +
2MeOH
—-
\=0
0)
+
MeO
Transesterification is a process where an ester is transformed into another through interchange of the alkoxy moiety (eq 2). Since the reaction is an equiRCOOR'
starting materials in transesterification. This reaction can be conducted under anhydrous conditions to allow employment of moisture-sensitive materials. Transesterification is applicable not only to the pure organic synthesis but also to polymerization, i.e. ring opening of lactones. Besides the laboratory utilization, transesterification has a long history in industry as well. Production of esters of oils and fats is very important and transesterification processes were shown to have worked early in this century. Transesterification also plays a central role in the paint industry such as curing of alkyd resins. In the middle of this century, the reaction between dimethyl terephthalate and ethylene glycol became a crucial step for polyester production although the process has almost been replaced by direct
+
R'OH
“•
