Trans-esterification reaction

One example of a new class of compound in this area is dioctyl carbonate (1, Table 4.9). The product is synthesized by the trans-esterification reaction of octa-nol and dimethyl carbonate in the presence of alkali catalyst (Fig. 4.20). Dioctyl carbonate (Cetiol CC) is a dry emollient with excellent dermatological compatibility and a comprehensive and convincing performance profile for various appli-... 

Yoda, K Catalysis of trans-esterification reactions, Makromol.Chem., 136, 311-313 (1970). 

Either the aglycone resulting from the action of a P-glucosidase or the glucoside, or possibly both, undergo cis-trans isomerization under influence of UV-light or possibly mediated by a dimethylallyl transferase. The last step of the biosynthetic pathway is an intramolecular esterification reaction, which can occur spontaneously, to yield coumarin (3.96). The enzymes that involved in these reactions have not been purified. 

Several important chemical reactions are catalyzed simply by H+ or OH ions. Examples include aldol reactions, esterifications and trans-esterifications, and... 

Nevertheless, the reagent is still used for a large number of esterification reactions of dextran. The synthesis of dextran amino acid esters is achieved by conversion of the polysaccharide in DMSO with the N-ben-zyloxycarbonyl protected acids for 48 h at 20 °C using DCC and pyridine. 0-(N-B enzyloxycarbonylglycyl) dextran with DS 1.1, 0-(AT-benzyloxycarbo-nyl-aminoenanthyl) dextran with DS 2.2, and 0-(N-acelyl-i,-histidinyl)dcx-tran with DS 1.1 are accessible. Deprotection was achieved with oxalic acid and Pd/C [190,191],... 

A large number of derivatives of the phosphonitrilic compounds can be prepared by means of the reactions at the P-Cl bonds. Hydrolysis reactions produce P-OH bonds that can then undergo esterification reactions. Substitution reactions that replace two chlorine atoms can occur at the same phosphoms atom (giving a geminal product) or on different phosphorus atoms. In the latter case, the two substituents can be on the same side of the ring in cis positions or on opposite sides of the ring in trans positions ... 

The 2-(trimethylsilyl)ethyl thioethers are stable towards trifluoroacetic acid under conditions typically used to cleave acetals. The standard acylation and trans-esterification reactions are also fully compatible. Many Lewis acids are tolerated but halogenating agents react. Mild conditions for the cleavage of 2-(trimethyl-sily )ethyl sulfides, which are compatible with many of the standard transformations in carbohydrate chemistry, entails treatment of the thioether in dichloro-... 

Figure 2 Details of two successive trans-esterification reactions. In the first step, the 2 -OH group of the branch point adenosine nucleophilically attacks the phosphate at the junction of the S exon and intron (S splice site), resulting in the formation of a new S -2 phosphodiester bond between the first nucleotide of the intron and the branch point adenosine (lariat structure formation) and breakage of an old 3 -S phosphodiester bond between the last nucleotide of the S exon and the first nucleotide of the intron (cut-off S exon formation). In the second step, the 3 -OH group of the cut-off S exon nucleophilically attacks the phosphate at the junction of the intron and 3 exon, ligating the two exons (mRNA formation) and releasing the lariat intron. The phosphates at the S splice site (red) and at the 3 splice site (green) and the branch point adenosine and its 2 -OH group are pictured. The lines represent the intron and boxes depict exons (El and E2).

Cellulose phosphites have also been synthesized by the reaction of cellulme with monomethylphosphite (72), which could proceed as either a trans-esterification reaction... 

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. 

Conventional, high temperature (trans)esterification reactions, as one can expect, are not suitable for the synthesis of the copolyesters we are concerned with(36). But polycondensation reactions between activated monomers may be adopted if the reaction proceeds reasonably fast even at a relatively low temperature(37). 

This process involves both direct esterification and trans-esterification reactions, and is carried to a sufficient extent of reaction to give a viscous liquid product, an oil-modified alkyd. 

The first step determines the functionality degree and can be tuned according to the needs of the target (trans)esterification reaction. The succession of the reaction conversions, as well as the assessment of the completeness of the reactions can be conveniently monitored by hr-MAS as illustrated... 

Gogate [151] also compares the energy efficiency of acoustic and hydrodynamic techniques with that of conventional reactors in the case of trans-esterification of vegetable oils. Cavitation can be successfully applied to trans-esterification reactions to afford a more than 90% yield of the product as per stoichiometry in a reaction time as low as 15 min. The technique hence appears to be very effective compared to the conventional approach. Hydrodynamic cavitation is about 40 times more energy efficient than acoustic cavitation and 160-400 times more efficient than the conventional agitation/heating/refluxing method. 

VL Discussion of the Principles Governing the Synthesis of Cellulose Esters by the Trans-esterification Reaction.124... 

The overall effect of the radicals of the substituents can be assessed by comparing the dissociation constants of the corresponding substituted acids data on the degree of substitution of various cellulose esters prepared by the trans-esterification reaction are presented in Table 11. 

The first approach to this problem was to attach the chiral auxiliary to the diene by a vinylogous trans-esterification reaction of chiral alcohols with the 3-alkoxy enones (Scheme 21). This reaction was used to construct a variety of chiral dienes including the menthol and phenmenthol dienes (55a) and (55b) by transesterification followed by enol silylation using the Simchen procedure (RsSiOTf taN). However, these dienes exhibit poor diastereofacial selectivity despite the precedent for high stereochemical control in homo Diels-Alder reactions by the use of similar auxiliaries on a,P-unsaturated enones. ... 

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-... 

RNA Splicing What is the ininimiim number of trans-esterification reactions needed to spUce an intron from an mRNA transcript Explain. 

Shah, P. A.V. Ramaswamy K. I,azar V. Ramaswamy. Synthesis and characterization of tin oxide-modified mesoporous sba-15 molecular sieves and catalytic activity in trans-esterification reaction. Appl. Catal. 2004, A 273, 239-248. 

The esterification reaction of jasmonic acid with methyl alcohol was carried out in a high-pressure reactor to reduce epimerization. It was known that the cis-form of methyl jasmonate easily epimerized to the trans-form of methyl jasmonate under acid, base and high temperature conditions. The resulting methyl jasmonate mixture was recovered and purified by solvent extraction followed by fractional distillation. To improve the methyl epijasmonate concentration, additional steps of fractionation, such as the use of silica gel, were applied. 

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