Showing papers on "Transesterification published in 1989"

Covalent immobilization of lipase in organic solvents.

Abstract: Lipase from Rhizopus sp. has been immobilized covalently on tresyl activated silica. Three different coupling media were evaluated: aqueous buffer, n-hexane, and a microemulsion based on n-hexane, aqueous buffer, and the nonionic surfactant triethylene glycol monododecyl ether. In addition, coupling via a very long, hydrophilic spacer arm, polyethylene glycol 1500 (PEG 1500), was compared with attachment to the silica via a short silane bridge only. The enzyme preparations were tested in hydrolysis and transesterification reactions. In the hydrolysis no marked differences in activity were found between the coupling media used. In the transesterification, on the other hand, the choice of immobilization medium had a very large effect on lipase activity, the preparation from microemulsion being the most active one. The use of the hydrophilic spacer had a large effect on activity in the hydrolysis reaction. Whereas direct coupling gave an activity of immobilized lipase of 26-34% of that of free enzyme, depending on the reaction medium, lipase bound via the spacer exhibited 56-67% activity. The latter values are considerably higher than previously reported in the literature for covalently immobilized lipase. The hydrophilic spacer had no effect on enzyme activity in the transesterification, however, a fact which is attributed to the hydrophobic medium of this reaction. The spacer is incompatible with the reaction medium and will, therefore, adsorb on the particles rather than stretch out into the bulk phase. The stability of the bound lipase was extremely good, no loss in activity being observed after a period of three weeks in aqueous solution of 37 degrees C.

Enzymatic transesterifications of carbonates in water-restricted environments.

Abstract: We investigated the ability of several hydrolases to catalyze reactions with an abiotic water-insoluble substrate, carbonic acid diphenyl ester, also known as diphenyl carbonate (DPC). In single-phase water/organic systems, turnover numbers (TN) of greater than 2 x 10(4) min(-1)have been achieved for the hydrolysis of DPC. The K(m) values for the hydrolytic reaction were measured to be 200 microM and 330 microM for Candida cylindracea lipase and Porcine liver esterase, respectively. In addition to hydrolysis, we observed transesterification of carbonates with a wide variety of alcohol and phenol species. Transesterifications of DPC with bifunctional alcohols resulted in the synthesis of polycarbonates. We investigated the stability and transesterification activity of these enzymes in several water-restricted environments to limit competing hydrolysis reactions. We find that, with the removal of water, hydrolysis is reduced more than four orders of magnitude while transesterification is diminished only 10-fold (turnover numbers of 600 min(-1) in water-miscible systems to 60 min(-1) in water-restricted environments with pure Candida lipase). Stability of the Candida lipase in these water-restricted environments (half-life of longer than 3 days) is much greater than in water/organic single phase systems (5 h in 20% methanol). In addition, the Candida lipase displayed enantiomeric selectivity in transesterifications of DPC with racemic 2-butanol (greater than 80% ee).

Preparation and properties of some water‐soluble, comb‐shaped, amphiphilic polymers

Abstract: Water-soluble comb-shaped polymers were prepared through grafting of poly(ethylene glycol) monomethyl ethers (MPEG) onto acrylic and methacrylic ester copolymers by transesterification reactions. The grafting was alkali-catalyzed, and performed in refluxing toluene solution or in melt at 155°C. The grafting efficiency was found to be on the order of 1 graft/10 monomer units. Epoxy groups in glycidyl methacrylate copolymers were also utilized for grafting. The crude graft copolymers were purified through chromatography and characterized by NMR and IR spectroscopy. Polymers prepared from MPEG 2000 were crystalline with melting points 10–15°C lower than the MPEG used. All polymers were shown to be surface active with CMC on the order of 1.5 g/L, and surface tensions of 38–45 dyn/cm. When used as emulsifiers the graft copolymers containing bulky lipophilic ester groups (2-ethylhexyl t-butyl) gave oil-in-water (o/w) and water-in-oil (w/o) emulsions from xylene/water with higher stability than those containing straight chain ester groups (methyl nbutyl n-docecyl). The most stable emulsions were obtained by dissolving the polymers in the organic phase.

Subtilisin-catalyzed transesterification in supercritical carbon dioxide

Abstract: Subtilisin Carlsberg was found to catalyze transesterification between N-acetyl-L-phenylalanine chloroethyl ester and ethanol in supercritical carbon dioxide. The effects of different temperatures and carbon dioxide/ethanol ratios on the reaction rate were investigated. A comparative study showed that enzymatic transesterification is faster in supercritical carbon dioxide than in anhydrous organic solvents.

Distannoxane as reverse micelle-type catalyst: novel solvent effect on reaction rate of transesterification

Abstract: La reaction est beaucoup plus rapide dans les hydrocarbures et les solvants halogenocarbones que dans les solvants polaires

Lipase Catalyzed Transesterification of Unsaturated Lipids in a Microemulsion

Abstract: A series of triglycerides having varying degrees of unsaturation of the acyl groups has been transesterified with stearic acid. It is shown that the position of the double bonds, not the degree of unsaturation, is the decisive factor in the rate of reaction. A A-6 double bond, which is present in petroselinic acid and ylinolenic acid, prevents reaction. Unsymmetrical triglycerides containing only one acyl group with δ-6 unsaturation reacts regiospecifically with the A-6 acyl group facing away from the enzyme. γ-Linolenic acid can be incorporated into an unhindered triglyceride through lipase catalyzed transesterification, indicating that the active site can in fact accommodate a δ-6 fatty acid, although not the corresponding triglyceride.

The Esterification of Carboxylic Acid with Alcohol over Hydrous Zirconium Oxide

Abstract: The esterification of carboxylic acids with alcohols proceeded efficiently with hydrous zirconium oxide to give the corresponding esters in the vapor phase, in the liquid phase, and in an autoclave. The steric hindrance of carboxylic acids and alcohols affected the esterification by lowering the reactivity. With a rise in the reaction temperature, the conversion of the carboxylic acid increased. The dehydration of alcohols was prevented by using hydrous zirconium oxide in spite of the high reaction temperature. The reaction rate is first-order with respect to the concentration of the catalyst and an alcohol and is inversely proportional to that of the carboxylic acid. Transesterification also proceeded efficiently.

Process for the extraction of polyunsaturated fatty acid esters from fish oils

Abstract: A process for the extraction of eicosapentaenoic (EPA) and docosahexaenoic (DHA) acid esters from crude fish oils, by means of transesterification with ethanol and H 2 SO 4 and two-step molecular distillation.

Oxime esters as novel irreversible acyl transfer agents for lipase catalysis in organic media

Abstract: Oxime acetates and acrylates are established as efficient irreversible acyl transfer agents for lipase-catalysed transesterification in organic media.

Polyvinyl oleate as a fat replacement

Abstract: Polyvinyl alcohol fatty acid esters, notably unsaturated acid esters, comprise a new class of edible fat replacements. Polyvinyl oleate, prepared either by direct esterification of low molecular weight polyvinyl alcohol with oleic acid, oleic anhydride or oleyl chloride, by the transesterification between low molecular weight polyvinyl alcohol and methyl oleate, or by the interesterification between low molecular weight polyvinyl acetate and methyl oleate, is a preferred edible fat replacement.

Production of monoglycerides by enzymatic transesterification

Abstract: A process for the production of high purity monoglycerides by lipase-catalyzed transesterification, and the products of the reaction, are described. In the method of the present invention, oils or pure triglycerides are combined with alcohol, a small amount of water and a lipase. The reaction proceeds under mild conditions, and produces high yields of β-monoglyceride product.

Preparation of esterified propoxylated glycerin by transesterification

Abstract: A novel method is provided for the preparation of food grade esterified propoxylated glycerin by tranesterification in a solventless system by reacting at temperatures of from about 100°C to about 250°C a propoxylated glycerin having from 2 to 100 oxypropylene oxide units per glycerin with a saturated or unsaturated C10 to C24 fatty acid ester or mixtures thereof.

The effect of crown ethers on enzyme-catalysed reactions in organic solvents

Abstract: Crown ethers considerably enhance the rate of the α-chymotrypsin-catalysed transesterification of N-acetyl-L-phenylalanine ethyl ester (N-Ac-L-Phe-OEt) with propan-1-ol in n-octane; with subtilisin the effect is somewhat less pronounced.

Production of polyol polyesters having reduced color content

Abstract: Polyol polyesters having reduced color content are prepared by base-catalyzed transesterification of lower (i.e., C₁-C₃) alkyl fatty esters having a carbonyl content of less than about 200 ppm with polyols. The esters can be prepared by a pretreatment com­prising distilling the said alkyl fatty esters (in a liquid state), preferably with a base, and discarding both the top cut in an amount that is about 5% or less and at least about 2% of the still bottoms.

Control of transesterification in polyester blends

Abstract: Polyester blends may undergo transesterification during processing, resulting in molecular rearrangements, transient properties, and eventually, degradation. To suppress transesterifcation, the use of organophosphites has been suggested in the patent and technical literature. The effectiveness of organophosphites, however, is variable and sometimes inconsistent. Our recent studies suggest a clue to the inconsistent behavior and provide a simple way to enhance the effectiveness of these stabilizers. Using solid state 31P NMR it was shown that for bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite a conversion of the phosphite group to a phosphonate, via hydrolysis, is a prerequisite for an effective inhibition of transesterification. This conversion occurs readily during melt compounding if the polymers are not completely dry. However, if rigorous drying is employed and phosphite conversion does not occur, then transesterification is not arrested. It was also found that over a period of time the conversion of the phosphite to a phosphonate may take place at room temperature as well. After aging for about a year in the laboratory, the originally ineffective compound, has become a very effective inhibitor of transesterification in blends containing poly(ethylene terephthalate), poly(butylene terephthalate), polycarbonate, and polyarylate. Thus, a simple way to enhance the phosphate effectiveness is to expose it to a humid environment prior to blending.

Molecular weight advancement of poly(ethylene ether carbonate) polyols

Abstract: Poly(ethylene ether carbonate) polyols have been prepared from ethylene carbonate and monoethylene glycol (MEG) or diethylene glycol (DEG) using sodium stannate trihydrate as catalyst. When these polyols (catalyst removed) are heated to elevated temperatures (< 180°C) at reduced Pressures, volatile impurities are removed, as distillate, molecular weight builds in a controllable manner. This is thought to be a transesterification process in which OC(O)CH2CH2OCH2CH2OH end groups on one molecule react with carbonate moieties on a second molecule with loss of DEG. These advanced polyols form rapidly with high CO2 retention and relatively low polydispersity. This process has been characterized by size exclusion chromatography, quantitative capillary gas chromatography of the distillates, 13C-NMR of the products, and alkaline hydrolysis of the products followed by quantification of the resultant glycols. The advanced polyols are largely alternating copolymers of DEG and CO2. They are valuable polyols for polyurethane fabrication.

Lipase catalysis in organic solvents transesterification of O-formyl esters of secondary alcohols

Abstract: Behaviour of the O-formyl esters of sterically hindered racemic secondary alcohols towards lipase-catalysed transesterification in organic solvents was studied. They react about 40–60 times faster than their respective O-acetates.

The activity of PEG-modified chymotrypsin in aqueous and organic media

Abstract: Polyethylene glycol-modified chymotrypsin was prepared by activation of monomethoxypolyethylene glycols with phenylchloroformates and subsequent coupling with free enzyme. The modification was correlated with enzyme activity in aqueous solution and in organic solvents. The activity in aqueous solution was high (80% of that of non-modified enzyme), even at high degrees of modification. The modified protease was soluble in benzene and DMF and catalyzed transesterification in cyclohexane.

Production of optically active esters and alcohols from racemic alcohols by lipase-catalyzed stereoselective transesterification in non-aqueous reaction system.

Abstract: Microbial lipase-catalyzed transesterification between vinyl acetate and (RS)-2-octanol or (RS)-1-phenylethanol was investigated in a reaction system without addition of aqueous or organic solvents. From a screening test with various lipases, it was found that the enzymes from Pseudomonas species could efficiently catalyze the reaction, and R-enantiomers of the racemic alcohols were preferentially esterified by them. Enantiomeric purities of the optically active alcohols (S) and esters (R) obtained from (RS)-1-phenylethanol by the stereoselective transesterification of these lipases were all more than 95%.

Quantitative analysis and determination of the enantiomeric purity of glycerides by 13C NMR spectroscopy. Application to the lipase‐catalysed transesterification of triacylglycerides

Abstract: 13 C NMR spectroscopy can be used for the quantitative analysis of mixtures of glycerides and the enantiomeric purity can be determined by using Eu(hfbc) 3 -d reagent. This technique was applied to the study of the reaction mixture obtained from the transesterification of tributyrin catalysed by My-lipase (Candida cylindracea). A «preference» of this lipase for the pro-R ester function of tributyrin is demonstrated

Enzymatic resolution of rac-1,1-dimethyl-1-sila-cyclohexan-2-ol by ester hydrolysis or transesterification using a crude lipase preparation of Candida cylindracea

Abstract: rac-2-Acetoxy-1,1-dimethyl-1-sila-cyclohexane (rac-2) was synthesized by esterification of rac-1,1-dimethyl-1-sila-cyclohexan-2-ol (rac-1) with acetic anhydride. Enantioselective hydrolysis of rac-2 in aqueous solution, catalysed by a crude lipase preparation of Candida cylindracea (EC 3.1.1.3), led to the formation of (S)-1 (95% ee). Enantioselective transesterification of rac-1 with triacetin in isooctane, catalysed by the same enzyme preparation, yielded (S)-2 (95% ee), which was separated by chromatography from non-reacted (R)-1 (96% ee). Recrystallization led to an improvement of the enantiomeric purity of (R)-1 and (S)-1 up to >98% ee. Thus the enantiomers of rac-1 were prepared (100 mg scale) with high enantiomeric purities by the use of two different types of enzyme-catalysed reaction.

Copolyester-diol polycarbonates, process for producing them and their use

Abstract: Copolyester-diol polycarbonates fluid at room temperature, having a number average molecular weight comprised within the range of from 1,500 to 6,000 with a glass transition temperature (T g ) lower than -45°C, useful in the sector of polyurethanes and in the sector of sealants, are obtained by means of a reaction of transesterification by starting from: (a) and organic carbonate, (b) an aliphatic diol, (c) an oligopolyester-diol. This latter is the product of reaction of an aliphatic bicarboxy acid with a mixture of two or more diols, comprising neopentyl glycol.

Process for the preparation of poly (vinylphenol) from poly (acetoxystyrene) by acid catalyzed transesterification

Abstract: Polymers of 4-vinylphenol are made by the acid catalyzed transesterification of polymers of 4-acetoxystyrene in an alcohol. The 4-vinylphenol polymers are useful as epoxy resins curing agents and as the phenolic base for epoxy resin per se.

Transesterification of triglycerides

Abstract: A process for converting liquid triglycerides into solid triglycerides by means of random transesterifications achieved through the use of catalytically active combinations comprising the reaction product of mixtures of dihydroxy and trihydroxy alcohols with mixtures of alkali metal hydroxides, and with ketones. The catalytically active materials can be employed in directed transesterifications in which the transesterification reaction mixture is subjected to a series of heating and cooling cycles during which higher melting fats are formed and precipitated from solution, causing an equilibrium shift that results in the formation and precipitation of still additional higher melting fats. An especially desirable catalytically active combination comprises the reaction product of 1, 2 propanediol, 1,3 propanediol and glycerol, with sodium hydroxide and potassium hydroxide, and in a preferred embodiment, the reaction product is combined with acetone to form the catalytically active combination.

Facile Synthesis of Trifluoromethyl Ketones by Palladium-Catalyzed Carroll Type Reaction

Abstract: Distannoxane-catalyzed transesterification of ethyl 4,4,4-trifluoroacetoacetate with allylic alcohols gave the corresponding allylic esters, which were subjected to palladium-catalyzed decarboxylat...

Melt transesterification of dimethyl terephthalate with ethylene glycol

Abstract: The kinetics of a semibatch melt transesterification of dimethyl terephthalate (DMT) with ethylene glycol (EG) is studied with zinc acetate as a catalyst. This paper quantifies the effect of various reactor operating conditions on the transesterification rate and the product composition distribution. Our experiments support the assumption that the methylesters in DMT and growing oligomer chains have the same reactivities for transesterification with EG and that the reactivity of hydroxyl groups in pure EG for esterification with DMT is twice that of the hydroxyl group in oligomers. With a molecular species model in which various oligomers are identified by the type of functional end groups, the progress of the transesterification and the oligomer concentration distribution were estimated and the agreement between the model predictions and the experimental data were excellent. It has also been shown that 30 wt. % of oligomers are produced for [EG]/[DMT] molar ratio of three, and up to 70 wt. % oligomers are produced at the [EG]/[DMT] molar ratio of one.