Ethyl transesterification with

Linalool can be converted to geranyl acetone (63) by the CarroU reaction (34). By transesterification with ethyl acetoacetate, the intermediate ester thermally rearranges with loss of carbon dioxide. Linalool can also be converted to geranyl acetone by reaction with methyl isopropenyl ether. The linalyl isopropenyl ether rearranges to give the geranyl acetone. 

The Traube synthesis represents but one of the many preparations that have been developed for purines. Transesterification of ethyl carboxamidoacetate with methyl urea affords the diamide... 

Mikolajczyk and coworkers have summarized other methods which lead to the desired sulfmate esters These are asymmetric oxidation of sulfenamides, kinetic resolution of racemic sulfmates in transesterification with chiral alcohols, kinetic resolution of racemic sulfinates upon treatment with chiral Grignard reagents, optical resolution via cyclodextrin complexes, and esterification of sulfinyl chlorides with chiral alcohols in the presence of optically active amines. None of these methods is very satisfactory since the esters produced are of low enantiomeric purity. However, the reaction of dialkyl sulfites (33) with t-butylmagnesium chloride in the presence of quinine gave the corresponding methyl, ethyl, n-propyl, isopropyl and n-butyl 2,2-dimethylpropane-l-yl sulfinates (34) of 43 to 73% enantiomeric purity in 50 to 84% yield. This made available sulfinate esters for the synthesis of t-butyl sulfoxides (35). 

Other esters of 2-chloro-2-cyclopropylideneacetic acid can easily be prepared from the methyl esters 1-Me, 2-Me by transesterification with the appropriate alcohol component under titanium tetraisopropoxide catalysis [20], as has been demonstrated for a number of benzyl and ethyl esters (Scheme 4) [9,10,21,22a]. 

The presence of small amounts of water was found to be essential even for hydrophobic ionic liquids (284). When a-chymotrypsin (in the form of salt-free lyophilized powder) was applied for the transesterification of Ai-acetyl-L-phenyl-alanine ethyl ester with 1-propanol in the dry ionic liquids [BMIM]PFg and [OMIMJPFg, little enzymatic activity was observed. The maximum activity was observed when 0.5 vol% water was added to the ionic liquids. Supercritical CO2 was also sufficient to activate the enzyme in dry ionic liquids. The addition of water to the supercritical C02-ionic liquid system further enhanced the enzymatic activity. 

The isolated dimethyl sebacate can be sold commercially as is or optionally hydrolyzed to sebacic acid. If a higher molecular weight plasticizer diester is required, a transesterification with -ethyl hexanol, for example, gives the desired product plus two equivalents of methanol which is recycled back to the oxycarbonylation reaction. If the free acid is desired, dimethyl sebacate hydrolysis to sebacic acid is carried out using a strong mineral acid such as sulfuric acid. Hydrolysis is nearly quantitative with a selectivity of about 99.5% to diacid and. 5% to the half-ester acid product. Additional recrystallization is used to improve purity if required. 

Based on a suggestion by Odell and Earlam [119] that crown ethers and cryptands can cause proteins to dissolve in methanol, Broos and coworkers [120] investigated the effects of crown ethers on the enzymatic activity of a-chymotrypsin in the transesterification reaction of N-acetyl-L-phenylalanine ethyl ester with n-propanol in organic solvents. They observed a 30-fold rate acceleration when 18-crown-6 was used in octane. At that time, it was proposed that the water- and cation-complexing... 

Fig. 16. Effect of degree of crosslinking (% DVB) of standard (non-porous) ion exchanger on initial transesterification rate, r° (mol kg-1 h-1), of ethyl acetate with 1-propanol [436]. (1) Liquid phase at 52°C initial composition (mole%), 0.4 ethyl acetate, 0.4 1-propanol, 0.2 dioxan (solvent). (2) Vapour phase at 120°C partial pressure of reactants, 0.5 bar (ester—alcohol ratio 1 1).

In liquid phase reactions, the importance of the swelling properties and the related sorption capacities for the catalytic activity of ion exchangers was demonstrated. The rate coefficient of 1-butanol—acetic acid esterification [431] decreased with the degree of crosslinking in the same manner as did the water sorption capacity and the solvation coefficient of 1-butanol. A similar effect was found for the transesterification of ethyl acrylate with 1-butanol [404]. 

These considerations can be formulated by schemes (e)—(g) below (R1 = H or alkyl). Scheme (e), in which the acid (ester) is protonated and alcohol reacts in non-adsorbed state, corresponds to the mechanisms Aac1 or Aac2 proposed for homogeneous esterification and hydrolysis with ion exchanger catalysts, the mechanism (e) was assumed to be operating in the liquid phase esterification of salicyclic acid with methanol [449] and in the transesterification of ethyl acetate with the same alcohol in dioxan as... 

In the case of subtilisin, the standard reaction is the transesterification of N-acetyl-L-phenylalanine ethyl ester with n-propanol [Eq. (12.12)]. 

When switching from water to an organic solvent, or switching between organic solvents, the substrate specificity can change. In the example of the standard reaction, transesterification of N-acetyl-i-phenylalanine ethyl ester with n-propanol by Subtilisin Carlsberg, which has been mentioned several times in this chapter already, the relative specificity between the rather hydrophobic phenylalanine compound and its more hydrophilic analog N-acetyl-L-serine ethyl ester varies with the solvent (Table 12.8) (Wescott, 1993). 

Fontes et al. (1998a) Batch Transesterification of IV-acetyl-L-phenylalanine ethyl ester with 1-propanol Subtilisin Carlsberg... 

Ethyl pentafluoroisopropenyl ether reacts in its resonance structure with sulfur trioxide in such a way that the sulfur atom of sulfur trioxide becomes attached to the terminal difluoromethylene group. The oxygen atom of sulfur trioxide combines with the methylene carbon of the ethyl group, and thus ethyl 2-oxopentafluoropropane-1 -sulfonate is formed. Its transesterification with trifluoroacetic acid affords 2-oxopentafluoropro-panesulfonic acid and ethyl trifluoroacetate [44],... 

First consider the base-catalyzed transesterification of ethyl benzoate with methanol. This is a classic example of nucleophilic acyl substitution by the addition-elimination mechanism. Methoxide ion is sufficiently nucleophilic to attack the ester carbonyl group. Ethoxide ion serves as a leaving group in a strongly exothermic second step. 

A mixture of methyl or ethyl fatty acid esters that is produced from fats and oils (triglycerides) by transesterification with methanol or ethanol. This mixture can be burned in most diesel engines without modifications, (p. 1205)... 

The catalytic properties were checked in the transesterification of ethyl propionate with n-butanol and in the Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate ... 

Transesterification of ethyl acetate with methanol NaOH, KOH, LiOH supported on mesoporous smectites [104]... 

Peptide synthesis. Vinyl esters of amino acids, prepared by transesterification with vinyl acetate, have been used as activated esters in peptide synthesis. The coupling reaction is best carried out in ethyl cyanoacetate, for this solvent suppresses the formation of colored products derived from liberated acetaldehyde. Racemization appears to be slight. 

For transesterification of ethyl acetate with various alcohols promoted by mixed organotin oxides, more detailed studies have been carried out on the structure and catalytic properties of supported tin dichloride and trichloride precursors, and on mixed organotin oxides of the type [P—(CH2) —SnBuCl]20. " " It was found that ring opening polymerization of e-caprolactone using the supported mixed organotin oxide, in the presence of propanol, required lengthy spacers (11 carbon atoms was found to be the best) between the polystyrene matrix and tin, in order to avoid the collapse of the resin beads (as observed for a six carbon spacer). The tin contamination could be reduced to <5 ppm in the final products when these types of catalysts were used in the transesterification of ethyl acetate and various alcohols. " ... 

Model reaction. The catalytic activity of all mentioned compounds has been investigated in the transesterification of ethyl acetate with n-octanol [Equation (6.1.1)], and in some cases with other alcohols as well. 

In addition to the hydrolysis of cocaine, the purified human liver cocaine methyl ester hydrolase also catalyzed the ethyl transesterification of cocaine with ethanol to form cocaethylene and methanol as shown in figure 1 (Dean et al. 1991 Brzezinski et al. 1994). Both the hydrolytic and the ethyl transesterification reactions increased as the two activities were analyzed in protein fractions obtained during the enzyme purifi-cation by column chromatography. This suggests that the separate activities are catalyzed by the same enzyme. The Km values for cocaine and ethanol of the purified enzyme at pH 7.3 were 116 M and 43 mM, respectively. The carboxylesterase also catalyzes the formation of ethyloleate from oleic acid and ethanol (Tsujita and Okuda 1992 Brzezinski et al. 1994). Other hydrolases or ester transferases have been reported to catalyze similar substrate "ethylation" reactions. 

Enantioselective esterification can be pressure dependent in supercritical fluoroform. For example, the selectivity of the transesterification of A -acetyl-phenylalanine ethyl ester with methanol catalyzed by Subtilisin Carlsberg was shown by Kamat et al. (26) to be greater at higher pressures than at lower pressures [Eq. (9)] ... 

Reactions with nucleotides have also been carried out in ionic liquids. In this context, the transesterification of iV-acetyl-L-phenylalanine ethyl ester with n-propanol catalysed by subtilisin (previously precipitated and rinsed with n-propanol) was succesfully carried out in [bmim+][PFg ] and [bmim+][BF ] (Fig. 7.4) [23]. 

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