Showing papers on "Transesterification published in 1994"

In situ preparation of fatty acid methyl esters for analysis of fatty acid composition in foods

Abstract: Lipid extraction preceding fatty acid methyl esters (FAME) preparation for gas chromatography is time-consuming and cumbersome. We omitted the lipid extraction and performed in situ transesterification (ISTE) by heating lipid-containing foods at 90°for 10 min after adding 0.5N NaOH in methanol for methanolysis and continued heating another 10 min for further methylation after adding 14% BF3 in methanol. FAME prepared by ISTE showed fatty acid composition virtually identical to FAME prepared after lipid extraction from powder, liquid, phospholipid-rich, and tissue products. Due to its simplicity, speed, and reduced organic solvent usage, ISTE should be useful to determine overall fatty acid composition of foods.

Development and Application of a Continuous Microwave Reactor for Organic Synthesis

Abstract: A laboratory-scale continuous microwave reactor (CMR) he been developed and used to conduct organic syntheses routinely, rapidly, and safely in a range of solvents, under pressures up to 1400 kPa and at temperatures up to 200 o C. Advantages and applications of the CMR are discussed, along with the rationale for the design. Reactions carried out with the CMR included nucleophilic substitution, addition, esterification, transesterification, acetalization, amidation, base- and acid-catalyzed hydrolysis, isomerization, decarboxylation, and elimination. Name reactions included the Michael addition, Hofmann degradation, Williamson ether synthesis, and the Mannich, Finkelstein, Baylis-Hillman, and Knoevenagel reactions

Kinetic resolution of acyclic 1,2-diols using a sequential lipase-catalyzed transesterification in organic solvents

Abstract: A method for the kinetic resolution of 3-(aryloxy)-1,2-propanediols rac-(1a-n) without additional protection-deprotection steps using a lipase-catalyzed sequential transesterification with lipase amano PS has been developed. In the first step of this one-pot procedure the racemic 1,2-diols are acylated regioselectively at the primary hydroxy group without enantioselection. The subsequent acylation at the secondary hydroxy group of the formed primary monoacetate is responsible for high enantioselection. The enantioselectivity of this transformation depends significantly on the substitution pattern of the aryl ring and the organic solvent used. 3-(Aryloxy)-1,2-propanediols with substituents in the para-position show a much higher enantioselectivity than the corres- ponding derivatives with ortho-substituents. Among other substrates, the pharmaceuticals Mephenesin, Guaifenesin, and Chlorphenesin have been resolved. The replacement of the aryloxy by an alkyl substituent causes a dramatic decrease of enantioselectivity

Lipase-catalyzed transesterification of rapeseed oil and 2-ethyl-1-hexanol

Abstract: Lipase-catalyzed transesterification (alcoholysis) of lowerucic acid rapeseed oil and 2-ethyl-1-hexanol without an additional organic solvent was studied in stirred batch reactors. Of a number of commercially available enzymes investigated, the best results were obtained with aCandida rugosa lipase. The optimal transesterification conditions were an oil/alcohol molar ratio of 1∶2.8, a minimum of 1.0% (w/w) added water, and with a temperature of 37–55°C. Under the optimal conditions, a nearly complete conversion was obtained in one hour with 14.6% (w/w) lipase, whereas 0.3% (w/w) lipase required 10 h for similar results. The enzyme was inactivated at 60°C.

Co) Polycarbonate and process for producing the same

Abstract: A processes for producing a (co)polycarbonate having a low terminal hydroxyl group concentration and being excellent in heat resistance and hue, which comprises melt-polycondensing a dihydroxy compound with a carbonic diester in the presence of a catalyst for transesterification selected from the group consisting of a nitrogen-containing basic compound, an alkali metal borate and an alkaline earth metal borate and in the presence of a specific ester compound.

Copolyester of cyclohexanedimethanol and process for producing such polyester

Abstract: Disclosed is a process for producing copolyesters having repeat units from a dicarboxylic acid component comprising at least 90 mol % terephthalic acid and a glycol component comprising about 10-95 mol % 1,4-cyclo-hexanedimethanol and from about 90-5 mol % ethylene glycol comprising reacting the dicarboxylic acid component and the glycol component at temperatures sufficient to effect esterification or transesterification and polycondensing the reaction product in the presence of a catalyst and inhibitor system consisting essentially of Mn, Zn, Ti, Ge and P, all parts by weight based on the weight of the copolyester.

RNA Cleavage and Phosphate Diester Transesterification by Encapsulated Lanthanide Ions: Traversing the Lanthanide Series with Lanthanum(III), Europium(III), and Lutetium(III) Complexes of1,4,7,10-Tetrakis(2-hydroxyalkyl)-1,4,7,10-tetraazacyclododecane

Abstract: 1,4,7,10-tetrakis(2-hydroxyethyl)-1,4,7,10-tetraazacyclododecane(THED) and (1S,4S,7S,10S)-1,4,7,10-tetrakis(2hydroxypropyl)-1,4,7,10-tetraazacyclododecane (S-THP) complexes of lanthanides were evaluated with their ability to promote transesterification of the 4-nitrophenyl phosphate ester of propylene glycol (1) or the cleavage of RNA oligomers. Kinetics of the reactions were measured and rate constants are reported.

Methyl ester from safflower seed oil of Turkish origin as a biofuel for diesel engines

Abstract: The primary problems associated with the use of pure vegetable oils as fuels in compression ignition (Diesel) engines are caused by high fuel viscosity. Transesterification of the oil with short-chain alcohols (such as methanol or ethanol) to corresponding fatty esters is the most promising solution to the high-viscosity problem. In this work, the transesterification method was applied to crude safflower seed oil of Turkish origin using methanol. The variables affecting the monoester yield, such as: were investigated. In the presence of 1.0 wt% KOH as the reaction catalyst, 97.7% ester yield was achieved within 18 min at a reaction temperature of 69 ± 1‡C using 1:7 vegetable oil-alcohol molar ratio. A significant improvement was observed in viscosity and other physical properties with the ester product compared to the parent vegetable oil. ASTM fuel properties of the methyl ester product were in accordance with those obtained for commercial Grade No.2-D diesel fuel.

Method for purifying alcohol esters

Abstract: Triglycerides, such as vegetable oils and animal fats, are esterified with alcohols to produce alcohol esters which can be used as alternative fuel sources. By-products of the transesterification reaction are stripped from the effluent of the transesterification reactor using a recovery alcohol that can be an isolated by-product of the transesterification reaction.

Recovery of tocopherols

Abstract: Starting from a mixture containing tocopherol, fats and/or fat derivatives, more particularly fatty acids, and optionally sterol and/or sterol derivatives, the free fatty acids present in the mixture are esterified with an alcohol. The mixture is then transesterified with an alcohol in the presence of a basic catalyst. After the transesterification, the excess lower alcohol is distilled off from the reaction mixture. The transesterification catalyst and the glycerol present, if any, are removed and the fatty acid alkyl ester is distilled off from the mixture. Distillation of fatty acid alkyl esters can be accomplished with a packed column in sequence with a wiped film evaporator. The simultaneous recovery of tocopherol and sterol is possible. Tocopherols and sterols can be separated by the crystallization of sterols from a blend of organic solvents.

Enzymatic fatty esters synthesis in aqueous medium with lipase from Candida parapsilosis (Ashford) Langeron and Talice

Abstract: The synthesis of fatty esters in aqueous medium by alcohoiysis catalysed by lipase from Candida parapsilosis (EC.3.1.1.3) is described. The transesterification of rapeseed oil with methanol leads to an equilibrium state after eight hours, with a yield (methyl esters formed/ total fatty acids initially present in the acylglycerols) of at least 53% (73, 45, 65% of the linolenic, linolek and oleic acids respectively). Yield was already about 42% after four hours of catalysis. This transesterification was permitted by methanol inhibition of hydrolysis of the esters.

Lipase-catalyzed synthesis of lysophospholipids in a continuous bioreactor

Abstract: A novel enzymatic method of lysolecithin synthesis was developed with immobilized lipase as a catalyst. The enzymatic transesterification was carried out in a number of alcohols, and the reaction was optimized with regard to the water content and temperature of the medium. Similar kinetics of transesterification were observed with several individual phospholipids. The reaction was also performed continuously in a packed-column bioreactor, which was operated for 1180 h. The lipase displayed strict regio-selectivity towardsn-1 fatty acid in the phospholipid molecule, thus yielding exclusivelysn-1 lysolecithins as the final product.sn-2 Lysophospholipids were subsequently obtained by acyl migration catalyzed by ammonia vapor. Advantages associated with the use of lipases as opposed to conventional, phospholipase-A2 catalyzed hydrolysis are briefly discussed.

Dramatic ligand effect in copper(II) complex promoted transesterification of a phosphate diester

Abstract: A cis-diaqua copper(II) complex has been shown to promote the transesterification of a phosphate diester with second-order dependence on the metal complex.

Quality control of rapeseed oil methyl esters by determination of acyl conversion

Abstract: A simple procedure for the evaluation of vegetable oil conversion to methyl esters of fatty acids has been developed. These methyl esters, prepared by the transesterification of vegetable oil with methanol, are used as alternative fuel for diesel engines. A method of gas-liquid chromatography (GLC) on packed columns is used to determine the conversion of acyls bound in acylglycerols to methyl esters. This procedure is based on comparison of the peak areas of methyl esters in fuel samples before and after reaction with an effective transesterification reagent, which will transform unreacted acylglycerols to methyl esters. A correlation between the bound glycerol content, determined by the thin-layer chromatography/flame-ionization detector method, and the acyl conversion, determined by GLC, is given. In acyl conversions to methyl esters over 96.0%, the bound glycerol content is less than 0.25% by weight.

Layer Structures. 2. Influence of Spacers on Chain Packing and Phase Transitions of Poly(ester-imide)s Derived from N-(4-Carboxyphenyl)trimellitimide

Abstract: Various poly(esterimide)s of N-(4-carboxyphenyl)trimellitimide were prepared by transesterification of its dimethyl ester with various aliphatic diols. The following spacers were used: combinations of different α,ω-dihydroxyalkanes, mirtures of 1,12-dihydroxydodecane and tetraethylene glycol, neat di-, tri-, and tetraethylene glycol, and diols containing sulfide groups. Poly(esterimide)s containing alkane spacers form layer structures in the solid state but neither monotropic nor enantiotropic liquid-crystalline (LC) phases. The three different kinds of solid state observed for these poly(esterimide)s were interpreted as frozen smectic-A, -B, and -E phases

Lipase-catalyzed synthesis of terpene esters by transesterification in n-hexane

Abstract: Short chain fatty acid esters of geraniol and citronellol were synthesized by lipase-catalyzed transesterification with yields as high as 98% molar conversion. Triacylglycerols were the best substrates and immobilized Candida antarctica lipase, SP435 gave the highest overall yields. The lipases tested successfully accommodated novel acyl donors such as isopropenyl acetate and glycidyl butyrate.

Method for the preparation of fatty acid alkyl esters

Abstract: A method for the preparation of fatty acid alkyl esters by transesterification, in particular catalytic transesterification, of triglycerides, wherein from a reaction mixture, in which the transesterification is carried out, an ester phase and a glycerol phase containing fatty acids, fatty acid salts and/or other fatty acid compounds are formed, which are separated from each other, characterized in that the fatty acids, the fatty acid salts and/or other fatty acid compounds are separated from the glycerol phase, esterified with an alcohol and recycled to a different reaction mixture, in which a further transesterification is carried out. The method according to the invention allows for a transesterification with a high yield of fatty acid esters.

Solvation of CBZ-amino acid nitrophenyl esters in organic media and the kinetics of their transesterification by subtilisin.

Abstract: Subtilisin Carlsberg adsorbed on silica particles has been used to catalyze the transesterification of CBZ–Ala–ONp and CBZ–Leu–ONp with 1–butanol in organic systems preequilibrated to water activity of 0.93. Initial reaction rates are conveniently followed by extraction of the released nitrophenol into an alkaline aqueous phase. Kinetic parameters were determined for varied ester concentrations in toluene, isopropyl ether, and hexane. The effect of solvent on substrate solvation was determined by solubility measurements. Much of the observed effect of solvent on Vm/Km may be accounted for by solvation differences. The residual effect of solvent on Km, after discounting solvation differences, is completely opposite to the apparent trend. © 1994 John Wiley & Sons, Inc.

Convenient Selective Monoacylation of 1,n-Diols Catalyzed by Ion-Exchange Resins

Abstract: Several 1,n-diols, ranging from 1,2-ethanediol to 1,16-hexadecanediol, were selectively monoacylated by transesterification in ester/octane solvent mixtures catalyzed by strongly acidic ion-exchange resins. This method of selective esterification is quite simple and practical. The selectivity for monoester formation and initial rates of monoester formation depended on the ester/octane ratio of the solvents. The reasons for the selectivity are as follows: (1) The sulfonic acid-type ion-exchange resins usually contain 50-80% water, and a strongly acidic aqueous layer is formed on the surface of the resins. (2) A partition equilibrium between the aqueous layer and the aprotic ester/octane layer is setup, and diols have higher partition coefficients than the product monoesters

Transesterification method using lipase powder with a particle diameter of 20-50 microns

Abstract: The transesterification method is conducted with a powdery lipase wherein the powdery lipase is dispersed in ester-containing starting materials in the presence or absence of an inert organic solvent, and the diameter of at least 90% of the dispersed lipase particles is kept in the range of 1 to 100 μm in the course of the trans-esterification reaction. A reactivity higher than that realized by the conventional transesterification method with a powdery lipase is obtained and the lipase can be easily recovered and reused, without causing a loss of the lipase activity, lowering of the conversion due to the residence of the substrate on the immobilizing carrier and side reactions caused by water introduced into the reaction system by the immobilizing carrier.

Enzymatic Synthesis of Various Aromatic Polyesters in Anhydrous Organic Solvents

Abstract: Lipases and proteases from various sources were tested in aromatic polyester synthesis in organic solvents. A commercial protease from Bacillus licheniformis efficiently catalyzed the transesterifica-tion of a diester of terephthalic acid and 1,4-butanediol in anhydrous tetrahydrofuran (THF). This protease was used as a catalyst in the synthesis of aromatic polyesters in THF. Oligomers with average molecular weights from 400 to 1000 daltons were obtained using various diols and aromatic diesters.

Selective Lipase-Catalyzed Esterification of Alkyl Glycosides

Abstract: Alkyl derivatives of glucose, galactose and fructose were acylated by lipase-catalyzed transesterification with alkanoic esters. The best results were obtained with immobilized Upases of the Candida antarctica type. Primary alcohol functions were acylated first, followed by secondary ones depending on the structure of the glycoside.The water activity in the reaction medium had a striking effect on both the rate and the selectivity of the process. The size and orientation of the alkyl substituent and the structure of the acyl acceptor were also found to exert a profound influence on the course of the reaction.

A comparison of different strategies for lipase-catalyzed synthesis of partial glycerides

Abstract: Four different approaches for the synthesis of monolaurylglycerol (MLG) by non specificPseudomonas cepacia lipase in a crude and purified form have been studied: a. The direct esterification of glycerol by lauric acid in bis-(2-ethylhexyl)sulfosuccinate sodium salt (AOT)/isooctane microemulsion systems; b. the transesterification of glycerol by vinyl laurate in the presence or not of any solvent; c. solid-phase glycerolysis of trilaurin; and, d. transesterification of protected glycerol, 1,2-O-isopropylidene glycerol, by vinyl laurate, in the presence or not of any solvent. It was found that in the two latter cases (d and c) the formation of pure MLG was occurred, while in the first two cases (a and b) apart of MLG the formation of DLG was also observed.

Organotin catalyzed transesterification

Abstract: Esters of monocarboxylic acids are transesterified with 1,2- and 1,3-polyols by reaction in the presence of a catalytically effective amount of a dialkyltin oxide blended with an excess of dialkyltin dichloride, so that a polyol ester of the monocarboxylic acid is formed. A transesterification reaction of alcohols and polyols with methyl or ethyl mono- or polycarboxylic acid esters utilizing a dimethyltin catalyst is also disclosed, in which the alcohol or polyol carboxylic acid ester formed is essentially free of the organotin catalyst. Carboxylic acid esters produced by the described methods, as well as carboxylic acid esters that are free of organotin catalysts are also disclosed.

Structure–activity relationships in the esterase-catalysed hydrolysis and transesterification of esters and lactones

Abstract: The Bronsted exponents for the alkaline hydrolysis of alkyl esters are 1.3 and 0.4 for substitution in the acyl and alcohol portions, respectively, which is indicative of a transition state which resembles the anionic tetrahedral intermediate with a localised negative charge. By contrast, the rate of the pig liver esterase (PLE)-catalysed hydrolysis shows little dependence upon the electron-withdrawing power of substituents. The values of kcat are independent of the pKa of the leaving group alcohol suggesting rate-limiting deacylation. There is a small steric effect of α-substitution in both the alcohol and carboxylic acid residues for the enzyme-catalysed reactions but the enzyme rate enhancement factor remains high for most esters. There is no substantial ee observed for the hydrolysis of racemic esters although the kinetic data can be used for determining the regioselective hydrolysis of diesters. Unsubstituted lactones are poor substrates for PLE but derivatives with hydrophobic substituents show kcat/Km values similar to those for acyclic esters. Dihydrocoumarin undergoes transesterification catalysed by PLE, kcat increases with increasing alcohol concentration indicative of rate-limiting deacylation. There is enantioselectivity in the PLE-catalysed hydrolysis of some racemic lactones but little or none in the transesterification of racemic alcohols with dihydrocoumarin.

Modification of Phospholipids with Lipases and Phospholipases

Abstract: Different commercial lipases and phosphoiipases were studied in the hydrolysis and transesterification of synthetic phosphatidylcholine and soybean lecithin. Wide variations in the lipase and phospholipase activities and in the protein contents of the preparations were observed. The substrate specificity varied between different enzymes. A high degree of hydrolysis of synthetic and soybean phospholipids was achieved with both types of enzymes.Enzymes immobilized on Celite were used in the transesterification of dimyristoyl phosphatidylcholine and oleic acid. The conversions were carried out both without solvent and in the presence of toluene. The amount of modified phosphatidylcholine was measured using HPLC. The highest amount of modified phosphatidylcholine was obtained in solvent-free transesterification. The best results were obtained with Aspergillus niyer lipase.