Esters by transesterification

Acrylic Esters. A procedure has been described for preparation of higher esters from methyl acrylate that illustrates the use of an acid catalyst together with the removal of one of the products by azeotropic distillation (112). Another procedure for the preparation of butyl acrylate, secondary alkyl acrylates, and hydroxyalkyl acrylates using -toluenesulfonic acid as a catalyst has been described (113). Alurninumisopropoxide catalyzes the reaction of amino alcohols with methyl acrylate and methyl methacrylate. A review of the synthesis of acryhc esters by transesterification is given in Reference 114 (see... 

J. K. Haken, Synthesis of Acrylic Esters by Transesterification Noyes Development Corp., Park Ridge, N.J., 1967. 

Ester alcoholysis (transesterification) in organic media is an equilibrium reaction and must be shifted in the desired direction. For example, Bornscheuer and coworkers [61] reported the resolution of ibuprofen vinyl ester by transesterification tvith n-hexanol in the presence of CAL-B. The vinyl alcohol generated during the reaction tautomerizes to acetaldehyde, thus making the reaction irreversible, as illustrated in Figure 6.14. 

Bradshaw A soapmaking process in which glyceryl esters (fats) are first converted to their corresponding methyl esters by transesterification, and then hydrolyzed. Invented by G. B. Bradshaw. 

Steroids [59-69] and a number of carbohydrates [70-73] also react with acyclic ortho esters to give cyclic ortho esters by transesterification. 

Keto acids and 2-alkyl- or 2-arylmalonic acids readily decarboxylate, and acylations with these proceed satisfactorily only at low temperatures. An alternative to direct acylation with /3-keto acids is thermolysis of acyl Meldrum s add (to generate an acylketene) in the presence of a nucleophile (Scheme 7.7). Esters of /J-keto acids can also be conveniently prepared from other keto esters by transesterification [27, 28],... 

Rogge, T.M. and Stevens, C.V., Facilitated synthesis of inulin esters by transesterification, Biomacromolecules, 5, 1799-1803, 2004. 

To obtain substantial yields of surfactant hydrophobes, especially in the most useful C12— 14 range, the choice is restricted to coconut, palm and palm kernel oils. In the C16-18 range, the same oils are also used but animal (normally beef) tallow can be used. The use of animal fats raises some ethical issues but these are not commonly used to produce anionic surfactants. The oils may be converted to methyl esters by transesterification which allows easier distillation to remove heavy/light fractions and the esters are finally hydrogenated to fatty alcohols. Alternatively, the fat or oil can be hydrolysed to fatty acid prior to esterification... 

Shieh et al. (2003) indicated a biodiesel transesterification using soybean oil and methanol and commercial immobilized lipase from R. miehei (Lipozyme IM-77). The response surface analysis showed that the following variables were important reaction time, temperature, enzyme amount, molar ratio of methanol to soybean oil, and added water content on percentage weight conversion to soybean oil methyl ester by transesterification. The optimum yield based on ridge max analysis gave a 92.2% weight conversion. 

Singh R, Nolan SP (2005) Synthesis of phosphorus esters by transesterification mediated by A-heterocyclic carbenes (NHCs). Chem Comm 2005(43) 5456-5458... 

Reichwein, J. F., Pagenkopf, B. L. New Mixed Phosphonate Esters by Transesterification of Pinacol Phosphonates and Their Use in Aldehyde and Ketone Coupling Reactions with Nonstabilized Phosphonates. J. Org. Chem. 2003, 68,1459-1463. 

Fig. 7.2 Stoichiometric scheme of kinetically controlled synthesis of esters by transesterification from vinyl esters and alcohols catalysed by CALB...

The release and obtention of esters by transesterification is another classical procedure to detach esterified compounds using, in this case, an alcohol or an alkoxide as the nucleophile. Care must be taken that water is excluded otherwise the acid will be obtain as a by-product [4]. Typical cleavage conditions involved the use of the desired alcohol in the presence of a non-nucleophilic base such as a tertiary amine (if primary or secondary amines are used, there is the risk of obtaining also the amide) [12] or the alkoxide dissolved in the corresponding alcohol or... 

The synthesis of alkyd resins using vegetable oils proceeds in two stages. For example, pentaerythritol, the tetraol of choice and mainly responsible for the degree of branching of the alkyd [64], and a vegetable oil are reacted to form an ester by transesterification. Then, a slight excess of phthalic anhydride is added to obtain a crosslinked alkyd resin (Fig. 3.21) [65]. Both reactions are monitored by acidity and viscosity measurements [66]. 

Fig. 5.5 3 Schematic representation of Crieco s reaction in a droplet microreactor. Photographs of droplet displacement during the Crieco s reaction are shown on the right ofthis figure. The droplet containing 1 was allowed to converge towards the droplet containing 2 and TFA. After mixing, the obtained droplet was directed towards the droplet containing 3, thus leading quantitatively to adducts 4 which could be cleaved to the corresponding methyl esters by transesterification.

Acetic acid Nitrous acid esters by transesterification... 

A monoester of sucrose prepared from a pure fatty acid methyl ester by transesterification is a mixture of positional isomers (15-20). Each isomer could behave differently in bread. Data in Figure 4 show a dramatic example of how positional isomers function differently in breadmaking (2) ). L-Ascorbyl 6-palmi-tate is an excellent dough strengthener, which showed a +92 cc volume response above a no-shortening control loaf (905 cc). On the other hand, L ascorbyl 2-palmi-tate decreased loaf volume 165 cc below the control. 

Orthoformic acid esters by transesterification with cleavage of 0,0-isopropylidene derivatives... 

Without additional reagents Mixed phosphorus esters by transesterification with halides... 

Sdteme 7. Cleavage of an amido boronic ester by transesterification. 

Figure 14.5 Preparation of fatty acid alkyl esters by transesterification.

Nishilddo et al reported two methods for the synthesis of a variety of carboxylic esters using Sn[N(S02C8Fi7)2]4 as a Lewis acid catalyst in FBS (Scheme 10.48) [73]. They showed that the Sn(IV) complex effectively functions for the preparation of carboxylic esters by transesterification from methyl esters with the corresponding alcohols, whereas Hf[N(S02C8Fi7)2]4 is more effective than Sn[N(S02C8Fi7)2]4 in the direct esterification of free carlx)xylic acids. 

The formation of PGEL and PGFL esters by transesterification occurs in the hermaphrodite gonad the esters are... 

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