Deperbnmt of ~ppled awmrl~by. okayam wivmny of . w ," "R ,
m a 700, Japan y m
Recehad octobsr 28, 1992 (Rwisej M a w t Reeslvad Msroh 15, 1993)
Contents I. Introduction 11. Acid Catalysts 111. Base Catalysts IV. Amine Catalysts V. Equlllbrlum and Use of Molecular Sleves VI. Lewis Acid and Metal Alkoxkle CatalystsVII. Titanium Tatraalkoxide Catalysts VIII. Organotin Catalysts IX. Use o 2pYridyl Esters f X. Miscellaneous Memods under Mild Conditions XI. kuolactonlzation X11. Enzymes A. OeneralFeatures B. Resoiutbn of Racemates C. Acylatbn of Poly01 Derivatives D. Laclonizatkm end Polycoycondensetlon XIII. Catalytic Antibody XIV. Conciudlng Remarks XV. References
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Junzo Otera received born a B.S. deqw in 1966 end a Ph.D. degw in 1971 from Osaka Unlversny. Helhen becamea research chemist at m a l Research L a b o r a W s of Kuraray CO. LM. He
movedtoOkayamaUnlvenltyofSclenceasanassoclateprofmfesscx in 1979 and has been a full professor since 1986. HIS research interesls are s y ~ t l appllcatbns ofcfganomelalllc and orgac nosulfucompounds. Fwtheseachievements.he wmmOChemlcBI Society of Japan awards twlce: technlcal devebpment of organotln catalyslforpolymerlzationofoxtamas.In 1985.anddlvislonalaward of industrlal organic ctmmlstry for novel heteroatom chemistry, in 1991.
Transesterification is one of the classic organic reactions that have enjoyed numerous laboratory usesand 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 carboxylicacids and alcohols. For instance, some carboxylicacids are sparingly soluble in organic solvents and accordingly difficult to subject to homogeneous esterification whereasesters 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 commerciallyavailable and thus they serve conveniently as starting materials in transesterification. This reaction can he conducted under anhydrousconditions 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 workedearly 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
esterification of terephthalic acid today.Notably, undimished potential of the transesterifimtion process even in the modem industry has been exemplified by a recent Chemical and Engineering News article: cosynthesis of ethylene glycol and dimethyl carbonate )l from ethylene carbonate and methanol (eq l.
Transesterification is a process where an ester is transformed into another through interchange of the alkoxy moiety (eq 2). Sincethe reaction is an equiRCOOR +
librium process, the transformation occura essentially by simply mixing the two components. However, it has long been known that the reaction is accelerated by acid or base catalysts. Bemuse of their versatility, the acid- or base-catalyzed reactions were the subjecta of extensive investigation, and the fundamental features were...