Trans-esterification studies

Some chemical properties of boryloxyphenylenephosphines (192) have been studied [Eq. (141)]. In Balueva et al. (91IZV2397) the intramolecular trans-esterification of phenylboric acid, a phenyl ester with a-... 

Other y-lactone containing systems that have been studied include derivatives of 3-oxabicyclo[3.1.0]hexan-2-one173 and 3-(2-hydroxybenzylidene)-4,5-dihydrofuran-2(3//)-one (213), which on irradiation in methanol undergoes a trans-cis photoisomerization followed by a photochemically induced trans esterification to give the coumarin (214).174... 

It is expected that if trans esterification occurs, the intrinsic viscosity of the samples will decrease and the rates of crystallization and ultimate degrees of crystallinity will also decrease. Therefore a series of studies on the 50/50 blend which was kept in the melt for 2, 3, 5, 7, and 10 minutes were performed. The crystallization was followed by DSC and IR. Simultaneous measurements of the intrinsic viscosity were made on a 40 60 mixture of 1,1,2,2,-tetrachloroethane phenol. The results are plotted in Figures 28, 29, and 30. 

A study of the possibility d synthesizing cellulose phosphites of a high degree of substitution by trans-esterification of readily available dimethylphosphite has been reported in the literature (7/). The transesterification of dimethylphosfdiite with cellulose may proceed in two ways ... 

No systematic studies of the principles governing the synthesis of cellulose esters by the trans-esterification reaction had been available in the literature until the present authom published work permitting one to ascertain the relation between the reactivity cf low-mol ular-weight esters and their structure, and the direction trf the reactions involved. 

The effect of the degree d xrlarization of the ester linkages in low-motecular-weight esters on their reactivity has been examined by studying the reaction of alcoholysis, with ceUulose, of methyl esters of benzoic, p-chloro-, p-hydroxy, p-hydroxy-, p- and o-nitrobenzoic acids, and those of phenyl-, phenoxy-, 2,4-dichlorophenoxy- and monodiloro-acetic adds. The trans-esterification reaction was carried out in non-aqueous dinrethylformamide in the presence of catalysts (sodium methylate, cadmium acetate, p-toluenesulphonic add) at 110-140° C. 

The present work summarizes the some results of these studies. The article describes some new types of cellulose ethers and esters, a number of mixed polysaccharides based on cellulose, which have been synthesized by the authors and their coworkers, and also discusses the principles governing a number of reactions for effecting the chemical transformation of cellulose, i.e. nucleophilic substitution, trans-esterification, ionic and free-radical addition, which enable new types of cellulose derivatives to be synthesized. 

Of the methods of synthesis of cellulose esters, the one that has been most thoroughly studied is the reaction of trans-esterification, and this method is widely used for the synthesis of low-molecular-weight esters. The alcoholysis of a low-molecular-weight ester (methyl- and n -propyl-borate) with hydroxyl groups of cellulose was first used (37) for die preparation of cellulose borate. This was followed by the trans-esterification, with cellulose, of the esters of phosphorous acids (see above), i.e. mono-, di- and trimethylphosphites (71, 72, 75), esters of phosphonic acids (76), and also phenyl-/ -chloroethyl- and / -fluoroethylphosphites (77, 78). Of considerable interest is the reaction of alcoholysis, with cellulose, of the esters of aryl- and naphthalenesulphonic add, which results in the formation of cellulose ethers, rather than esters (79-81). 

The study of posttranscriptional processing of RNA molecules led to one of the most exciting discoveries in modern biochemistry—the existence of RNA enzymes. The best-characterized ribozymes are the self-sphcing group I introns, RNase P, and the hammerhead ribozyme (discussed below). Most of the activities of these ribozymes are based on two fundamental reactions trans-esterification (Fig. 26-13) and phosphodiester bond hydrolysis (cleavage). The substrate for ribozymes is often an RNA molecule, and it may even be part of the ribozyme itself When its substrate is RNA, an RNA cat-... 

For example, Mikolajczyk and Kielbasinski [172-175] studied the acylation of phosphine boranes 259 using CAL (Chirazyme ) lipase from Candida Antarctica and Lipase AK from Pseudomonas fluorescencs (Scheme 84). The best enantios-electivity was attained in the lipase AK-catalyzed acylation of 259 in cyclohexane solution with vinyl butyrate as an acyl donor (99% ee) for unreacted hydroxypho-sphinate 259 and 43% ee for the acylated product 260. The E-values were on the level of 15. The enzymatic resolution of alkoxy (hydroxymethyl)phenyl-phosphine boranes (/ /S)-261 was achieved by trans-esterification with vinyl acetate in the presence of CALB, Amano AK, Amano PS, Amano AH, and LPL in various solvents. The best enantioselectivity of imreacted alcohol 261 and acylated product 262 was attained in cyclohexane (37% ee, conversion 50%). Kielbasinski [176] recently reported some additional data, including theoretical calculations and more accurate chemical correlation, which proved that the borane reduction of acyclic phosphine oxides proceeded with inversion of configuration at the phosphoms center. On this basis, the stereochemistry of the enzymatic reaction was ultimately determined (Scheme 85). 

Anilkumar, A.T., Sudhrr, U., Joly, S., and Narr, S.M. (2000) Studies in lipase catalyzed trans-esterifications synthesis of (+)-albicanol, (+)-albicanyl acetate and chiral intermediates useful in the synOiesis of drimanes and labdanes. Tetrahedron, 56,1899-1903. 

Transesterification has been carried out in many laboratory and industrial applications involving synthesis of esters and is by far the most useful and exploited reaction used with enzymes in organic solvents [96]. Lipases are especially well suited to catalyze trans-esterifications in organic solvents [97], although other hydrolases have been studied for... 

The purpose of this report is to provide an analysis of the synthesis and characterization of new high-heat, ductile poly(ester-carbonate-siloxane) materials via reactive extmsion with a trans-esterification catalyst. The two resins that were used in this study were derived from a high-heat poly(ester-carbonate) (PEC) and polycarbonate-... 

Bowden94 studied the transmission of substituent effects through C=C in the esterification of 3-substituted acrylic acids with diazodiphenylmethane (DDM) and in the ionization of the same acids. The ap values of the substituents were used to characterize their electronic effects for Hammett-type correlations. In esterification with DDM at 30 °C, the p values of the trans acids and the cis acids were 1.682 and 1.772, respectively, in ethanol... 

Although the past three years have witnessed many ingenious syntheses of the two insect juvenile hormones, the preparation of the naturally-occurring dextrorotatory Cl8 hormone (cis-epoxide) has only recently been achieved. Indeed, in two independent studies, both enantiomeric pairs of the cis- and trans-epoxides. have been prepared and it has been firmly established that the two chiral centres have the 10R,11S configurations in the naturally-occurring material. Findlay et al. have now published full details of their previously announced synthesis of the two juvenile hormones and other double-bond isomers. In an earlier synthesis of the C18 hormone, Corey et al. used the dienol (30 R = Et) as a key intermediate and now they have described two new stereospecific routes to this compound (Scheme 2). In the first synthesis the lactone (27) was converted into the hydroxy-olefin (28) by hydrolysis, esterification, tosylation, and lithium... 

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