Showing papers on "Transesterification published in 1993"

Preparation of ester derivatives of fatty acids for chromatographic analysis

Abstract: A. Introduction B. Acid-Catalysed Esterification and Transesterification 1. General mechanism 2. Methanolic hydrogen chloride 3. Methanolic sulfuric acid 4. Boron trifluoride-methanol 5. Other acidic catalysts C. Base-Catalysed Transesterification 1. General mechanism 2. Sodium and potassium methoxide catalysts 3. Organic base catalysis D. Diazomethane and Related Reagents 1. Diazomethane and methyl ester preparation 2. Preparation of UV-absorbing and other derivatives E. Pyrolysis of Tetramethylammonium Salts of Fatty acids for the Preparation of Methyl Esters F. Preparation of Esters and Amides via Activated Fatty Acids 1. Acid halides 2. Fatty acid anhydrides 3. Imidazolides 4. Other coupling reagents G. Reaction of Alkyl or Aryl Halides with a Base 1. Derivatives for gas chromatography 2. Phenacyl esters and other derivatives for high-performance liquid chromatography H. Alternative Methods for the Preparation of Esters, Amides and Other Fatty Acid Derivatives 1. Dimethylsulfate with dicyclohexylamine 2. Preparation of esters with alkyl formamide derivatives 3. Trimethylsilyl esters 4. Preparation of pyrrolidides from esters 5. Preparation of hydroxamic acid and related derivatives 6. Reaction with Grignard reagents I. Special Cases 1. Short-chain fatty acids 2. Fatty acids with unusual structures 3. Sphingolipids and other N-acyl lipids 4. Sterol esters 5. Selective esterification of free fatty acids in the presence of other lipids J. Preparation of Esters in the Presence of Adsorbents for Thin-Layer Chromatography K. Simultaneous Extraction from Tissues and Transesterification L. Artefacts of Esterification Procedures M. The Choice of Reagents a Summary

Process for the continuous production of lower alkyl esters of higher fatty acids

Abstract: Production of lower alkyl esters of higher fatty acids from an oil phase and lower alcohols by catalytic transesterification at reaction temperatures of up to 100° C. in the presence of an alkaline catalyst, includes a) introducing a mixture of oil phase, alcohol and catalyst at reaction temperature into the top of a first reactor column, at a rate of flow which is lower than the sinking rate of the glycerine separated from the reaction mixture, b) the reaction mixture is passed into a second reactor for further transesterification, c) the thus obtained reaction mixture is further freed of glycerine in an initial separating stage by means of a short-term washing, d) the reaction mixture is passed into a third reactor with addition of further alcohol and catalyst, and at a rate of flow conforming to the first stage of the process, e) the reaction mixture is further transesterified, f) reaction product is freed of the remaining methanol, glycerine, soaps formed and catalyst in a second separating stage, under addition of an aqueous extraction buffer solution, and g) the reaction mixture is freed of lower alcohols by stripping, washed with suitable extraction and washing solutions and dried.

Coordination polymerization of lactides, 4. The role of transesterification in the copolymerization of L,L‐lactide and ε‐caprolactone

Abstract: Two modes of transesterification in copolymerization of L,L-lactide with e-caprolactone in the presence of initiators containing Al and Zn were found. The quantitative analysis of the contributions of both types of transesterification reactions is revealed. The transesterification ability of initiators containing zinc is greater than that of initiators containing aluminium. Decrease of the reaction temperature tends to reduce both the first and the second mode of transesterification, leading to an elongation of blocks in the copolymer chains.

Macromolecular engineering of polyactones and polyactides. 12. Study of the depolymerization reactions of poly(.epsilon.-caprolactone) with functional aluminum alkoxide end groups

Abstract: Ring-opening polymerization of e-caprolactone he been initiated with functional aluminum alkoxides in toluene at 25°C. Degradation of «living» polyester chains by transesterification reactions he been studied in relation to temperature, solvent polarity, average molecular weight, and structure of the initiator, i.e., the nature of the functional group and the number of alkoxides per Al atom. Degradation products, particularly cyclic oligomers, have been isolated by supercritical fluid extraction (SFE) and characterized by GC-MS. The effect of Lewis bases on transesterification reactions he been investigated and discussed in reference to the «coordination-insertion» mechanism

Marked dependence of enzyme prochiral selectivity on the solvent

Abstract: Prochiral selectivity of various hydrolytic enzymes (lipases and proteases) in organic solvents was investigated in transformations involving a 2-substituted 1,3-propanediol or its diester. In two instances, a significant dependence of enzyme prochiral selectivity on the solvent was found: transesterification of diol 1 with vinyl butyrate catalyzed by Aspergillus oryzae protease in anhydrous solvents and hydrolysis of diester 3 catalyzed by Pseudomonas sp. lipase in hydrated organic solvents (monoester 2 was a product in both reactions)

A novel reaction medium : perfluorocarbon fluids

Abstract: The use of perfluorocarbon (PFC) fluids such as perfluorinated alkanes and alkylamines as inert medium for organic reactions is demonstrated with advantages summarized. PFC fluids have been found to be very useful in organic reactions where a medium is needed for refluxing and for separating a low boiling component, or where an extremely nonpolar/inert medium is required for reactions carried out under vigorous conditions. The PFC fluids are not miscible with most organic compounds and therefore offer good separatory properties that common organic solvents do not have

Pour point depressants for industrial lubricants containing mixtures of fatty acid esters and vegetable oils

Abstract: This invention relates to a composition containing the combination of: (A) at least one vegetable or synthetic triglyceride, (B) esters from the transesterification of at least one animal or vegetable oil triglyceride, (C) a pour point depressant, and (D) a performance additive. The composition may optionally contain (E) other oils.

Factors affecting the lipase catalyzed transesterification reactions of 3-hydroxy esters in organic solvents.

Abstract: Chiral resolutions of racemic 3-hydroxy esters were performed in organic phases with lipases from Pseudomonas cepacia , Chromobacterium viscosum and Porcine pancreas. The reaction conditions have been optimized with 3-hydroxy octanoic acid methyl ester. Different organic solvents have been tested showing a tendentious correlation with the hydrophobicity of the solvents expressed as log P. The reaction time was shortened six fold by using irreversible acylating agents. We have found solvent type, lipase type and acylating agent acting as tools for changing the enantioselectivity. Lipase from Pseudomonas cepacia was lyophilized at different pH and the influence of the amount of water added was investigated, resulting in the highest activity at the pH optimum and a denaturation of the lipase above 1 % water (w/w lipase ). The water activity was measured on-line with a humidity sensor. Water activities greater than 0.4 led to a decrease in enantioselectivity and reaction rate. In the optimized system the resolutions of other 3-hydroxy esters were tested. Aliphatic compounds reacted with lower enantioselectivity, only the substrates could be isolated in high enantiomeric purity. In contrast, aromatic 3-hydroxy esters were acylated by lipases with high stereoselectivity. A model of the active site of lipase from Pseudomonas sp . explained these experimental observations.

Effects of water activity on Vmax and KM of lipase catalyzed transesterification in organic media

Abstract: The Vmax and KM of various forms of lipase from Pseudomonas cepacia (powder, adsorbed onto Celite or covalently linked to polyethylene glycol) were determined in organic solvents preequilibrated to water activities (aw) from <0.1 to 0.84. The model reaction was the transesterification between n-octanol and vinyl butyrate. It was found that KM for the nucleophile increased with increasing aw for all three lipase forms. Vmax increased with increasing aw for polyethylene glycol-lipase, whereas there was an optimum at intermediate aw values (0.11 – 0.38) for lipase powder and Celite-immobilized lipase.

Transesterification process to manufacture ethyl ester of rape oil

Abstract: A process for the production of the ethyl ester of winter rape [EEWR] for use as a biodiesel fuel has been studied. The essential part of the process is the transesterification of rape oil with ethanol, in the presence of a catalyst, to yield the ethyl ester of rape oil as a product and glycerin as a by-product. Experiments have been performed to determine the optimum conditions for the preparation of EEWR. The process variables were: (1) temperature, (2) catalyst, (3) rate of agitation, (4) water content of the alcohol used, and (5) the amount of excess alcohol used. The optimum conditions were: (1) room temperature, (2) 0.5% sodium methoxide or 1% potassium hydroxide catalyst by weight of rapeseed oil, (3) extremely vigorous agitation with some splashing during the initial phase of the reaction and agitation was not necessary after the reaction mixture became homogeneous, (4) absolute ethanol was necessary for high conversion, and (5) 50% excess ethanol with NaOCH{sub 3} or 100% excess with KOH gave a maximum conversion. Viscosity, cloud point and pour point of the EEWR were measured. A preliminary break-even cost for the commercial production of EEWR was found to be $0.55/liter [$2.08/US gallon].

Lipase-catalyzed modification of phospholipids: Incorporation of n-3 fatty acids into biosurfactants

Abstract: Phospholipids were successfully modified by lipase-catalyzed transesterification to incorporate n-3 polyunsaturated fatty acids such as eicosapentaenoic acid (20:5) and docosahexaenoic acid (22:6). The phospholipid modification was carried out in organic media with lipase fromMucor miehei (lipozyme) as biocatalyst. The parameters studied were the effect of different solvents, enzymes, acyl donor type, phospholipid class, water, enzyme and substrate concentrations. Hydrolysis of phosphatidylcholine to yield lysophosphatidylcholine and the synthesis of phosphatidylcholine from lysophosphatidylcholine was also carried out. The optimal conditions for the modification of phospholipids by transesterification were obtained with phosphatidylcholine and free eicosapentaenoic acid EPA 45 as acyl donor in the presence of 15% w/w nonimmobilizedMucor miehei lipase (lipozyme) in hexane with no added water. The maximum incorporation of EPA 45 was 17.7 mol%. Hydrolysis was easily achieved with phospholipase A2 in benzene and Tris-HCl buffer. The synthesis of phosphatidylcholine was difficult, and when it was achieved, not enough phosphatidylcholine was obtained for quantitation.

Transesterification of cocoa butter by fungal lipases : effect of solvent on 1,3-specificity

Abstract: Transesterification and alcoholysis reactions catalyzed by immobilized lipases fromMucor miehei andHumicola lanuginosa in hexane gave fatty acid esters that did not reflect the expected 1,3-specificity of the enzymes, due to competing acyl migrations in the partial glyceride products. However, both lipases were 1,3-specific in reactions when diethyl ether was used as a solvent, and this provided a convenient analytical methodology in combination with gas chromatography and nuclear magnetic resonance spectroscopy for the determination of fatty acid distribution within triglycerides.

Lipase-catalyzed synthesis of partial glyceride

Abstract: Mucor miehei (IM 20) and Candida antarctica (SP 382) lipases were used for esterification of free fatty acids in the absence of organic solvent or transesterification of fatty acid methyl esters in hexane with isopropylidene glycerols. Acid catalyzed cleavage of the isopropylidene groups resulted in the formation of monoacyl glycerol (MAG) and diacyl glycerol (DAG). Both oleic (18:1 n-9) and eicosapentaenoic acid, EPA (20:5 n-3) were successfully incorporated into glycerides. Total acyl donor conversion ranged from 46.9 – 96.9% with MAG content of up to 88.5%.

Enzymatic transesterification of rapeseed oil and lauric acid in a continuous reactor

Abstract: The optimum conditions for enzymatic transesterification of rapeseed oil and lauric acid in a fixed-bed reactor were studied. No solvent was used in the reaction mixture. A small amount of water was dissolved in the substrate mixture to maintain the activity of the enzyme at as high a level as possible. For maximum yield, the transesterification was performed with a residence time of about 20 min at a water content in the range of 0.1 to 0.2% and at the lowest possible temperature.

Water activity does not influence the enantioselectivity of Lipase PS and lipoprotein lipase in organic solvents

Abstract: The activity and enantioselectivity of Lipase PS from Pseudomonas cepacia and lipoprotein lipase from Pseudomonas sp. were investigated in organic solvents preequilibrated to water activities ranging from <0.1 to 0.53, using as a model reaction the transesterification between (±)-sulcatol and vinyl acetate. Variations of water activity markedly influenced the transesterification rate but did not modify the enantioselectivity of the two enzymes.

Synthesis and characterization of a new biodegradable semi-solid poly(ortho ester) for drug delivery systems

Abstract: Since the late 1970s, three families of poly(ortho esters) (POE) were synthesized to provide bioerodible carriers for drug delivery devices. The most recent POE is a semi-solid polymer with a viscous behavior at room temperature. Polymer synthesis by a transesterification reaction between a triol and a trialkyl orthoester is described. The structure of the polymer was confirmed by conventional methods such as 1H-NMR, 13C-NMR and FT-IR. Information concerning average molecular weight and intrinsic viscosity was obtained respectively by GPC and viscosimetry. Residual solvents in the polymer were determined using gas chromatography. The chromatographic conditions were optimized to enable the quantification of the solvents in concentrations of a few percent. The mechanical behavior of the semi-solid POE was determined by rheometric measurements. Hydrolysis of the polymer leads to the formation of the original triol and the carboxylic acid derived from the trialkyl orthoester used in the transesterification st...

Removal of boronic acid protecting groups by transesterification

Abstract: A method for the removal of ester protecting groups from α-amino boronic acid is disclosed for the preparation of compounds of the formula: R1-Xn-NHCH(R2)-B(OH)?2?.

Synthesis of enantiomerically pure (R)-2-cycloalken-1-ols using highly enantioselective enzymatic transesterification

Abstract: Optically pure (R)-2-cycloalken-1-ols were synthesized via highly enantioselective lipase-catalyzed transesterification of 2-substituted cycloalkanols.

Recovery of tocopherol and sterol from tocopherol and sterol containing mixtures of fats and fat derivatives

Abstract: A process is provided for simultaneously recovering tocopherol and sterol from a mixture containing tocopherol, fats and/or fat derivatives, more particularly fatty acids, and sterol and/or sterol derivatives, more particularly from a steamer distillate of natural oils and fats. The steps of said process comprise: free fatty acids present in the mixture are esterified with a lower alcohol, preferably methanol, 0.4 to 1.6 and more particularly 1 to 1.5 parts by volume of mixture being esterified with 1 part by volume of the lower alcohol, the mixture is subsequently transesterified with the lower alcohol in the presence of a basic catalyst, the excess lower alcohol is distilled off from the reaction mixture after the transesterification, the transesterification catalyst and the glycerol optionally present are removed, more particularly by washing, the fatty acid alkyl ester is distilled off from the mixture, more particularly after removal of the transesterification catalyst, and if desired, tocopherol and sterol are separated by methods known per se. After the transesterification reaction, the alkali catalyst is preferably neutralized with an inorganic acid and the mixture is then washed with water.

Fluorinated ketene dithioacetals. 2. Synthesis of 2-hydroperfluoro acid derivatives from perfluoroketene dithioacetals

Abstract: Perfluoroketene dithioacetals were prepared in high yields from perfluoroaldehyde hydrates via their thioacetalization (TiCl 4 /CH 2 Cl 2 ) followed by basic phase transfer catalysed HF elimination. Acidic hydrolysis (CF 3 CO 2 H, H 2 O) and then transesterification (EtOH, Ti(OiPr) 4 ) yielded S-alkyl 2-hydroperfluoro thioesters and ethyl 2-hydroperfluoro esters, respectively

Degradative transesterification of terephthalate polyesters to obtain DOTP plasticizer for flexible PVC

Abstract: It has been found that dioctyl terephthalate (DOTP), a plasticizer for polyvinyl chloride (PVC), can be made from scrap terephthalate polyesters such as polyethylene terephthalate (PET) by a method known as degradative transesterification. It is recognized that this plasticizer is as good as plasticizer as commercial DOTP, and that it may potentially replace dioctyl phthalate (DOP). The production of DOTP from scrap PET is shown to be cost effective. The use of this technology may provide a solution to a part of our solid-waste problem.