Showing papers on "Transesterification published in 1988"

Lipase-catalyzed irreversible transesterifications using enol esters as acylating reagents: preparative enantio- and regioselective syntheses of alcohols, glycerol derivatives, sugars, and organometallics

Abstract: Lipase-catalyzed transesterification of the prochiral symmetric dialcohol (I) in an organic medium yields the optically active monoacetate (S)-(III) together with the diacetate (IV); the isopropenyl alcohol freed from (II) during the transesterification rapidly tautomerizes to volatile acetone, making the process irreversible and simpler for product isolation.

Production of biosurfactants from sugar alcohols and vegetable oils catalyzed by lipases in a nonaqueous medium

Abstract: Porcine pancreatic and Chromobacterium viscosum lipases catalyze transesterification reactions between a number of sugar alcohols and various plant and animal oils in dry pyridine. The products of this process have been identified as primary monoesters of sugar alcohols and fatty acids. These enzymatically prepared sugar alcohol esters have been found to be excellent surfactants in terms of their ability to reduce interfacial and surface tensions and to stabilize emulsions.

Lipase catalyzed formation of flavour esters

Abstract: Thirteen commercial lipase preparations were checked for their ability to catalyse the formation of flavour esters (isoamyl or geranyl acetate, propionate and butyrate) by either direct esterification or ester solvolysis in n-heptane. The formation of isoamyl or geranyl butyrates and propionates by direct esterification was catalyzed by the majority of the tested lipases. Acetic acid esters were more difficult to obtain. Transesterification reactions were found to be a good alternative way for ester synthesis.

Lipase-catalyzed irreversible transesterification for preparative synthesis of chiral glycerol derivatives

Abstract: L'utilisation de lipase pour catalyser les reactions d'esterification et de transesterification, est un moyen efficace pour synthetiser et differencier des molecules enantiomeriques. Un exemple de synthese de derives acyles de meso-1,3-diols enantiomeres, utilisant cette technique de transesterification irreversible catalysee par une lipase, est presente

Process considerations of continuous fat modification with an immobilized lipase

Abstract: Lipases will catalyze the incorporation of new fatty acids into the triglyceride component of a fat (acidolysis) or can rearrange/redistribute the existing fatty acid radicals in the fat’s triglycerides (transesterification). Both processes can dramatically change the physical characteristics of the fat. Immobilization of the lipase allows for the use of the catalyst in a continuous column operation. Examples illustrating the commercial utility of such immobilized enzymes are presented. Process configurations, scale-up issues and catalyst lifetime/productivity are discussed.

Morphological-studies of Polycarbonate-poly(butylene Terephthalate) Blends By Transmission Electron-microscopy

Abstract: The morphology of polycarbonate (PC)-poly(butylene terephthalate) (PBT) blends prepared by melt-processing in an extruder or a Brabender Plastograph was studied by Transmission Electron Microscopy. Transesterification during blending was avoided by the use of di-n-octadecyl phosphite, an efficient transesterification inhibitor. Ruthenium tetraoxide was used to selectively stain the PC fraction. Observation of ultrathin sections revealed the biphasic nature of the blends and the partial compatibility of the polymers in the molten state. The most striking consequence of this Is the presence, of PBT crystalline lamellae growing inside the PC-rich phase for samples annealed in the proper temperature range. A preliminary study of the morphology as a function of composition and thermal annealing was undertaken. The RuO4 staining technique was also applied to the commercial blend Xenoy CL 100 from General Electric, which was shown to contain an MBS impact modifier (a methylmethacrylate butadiene-styrene copolymer) exclusively located In the PC-rich phase.

Tetramethylguanidine catalyzed transesterification of fats and oils: A new method for rapid determination of their composition

Abstract: A new method for the rapid preparation of methyl esters from vegetable oils and fats, using tetramethylguanidine as catalyst, has been developed. This method is compared with the traditional method (Ce 2–66, using 20% BF3 in methanol) and that proposed by Hartman and Lago (using NH4Cl/H2SO4 in methanol). It is shown that the new method produces the methyl esters in quantitative yields and has certain advantages, as it is simpler, cheaper and does not result in isomerization of the fatty acids.

Process for the preparation of quaternary esteramines and their use

Abstract: In the process described, glycerides are subjected to transesterification with alkanolamines and the transesterification product obtained is quaternised. The ester amines thus obtained are suitable in particular as fabric softeners, cosmetic foundations and softeners for textiles.

Process for the synthesis of polyol fatty acid polyesters

Abstract: The invention pertains to a process for the synthesis of polyol fatty acid polyesters involving transesterification of a reaction mixture comprising a soap emulsifier in which during the reaction at a degree of conversion within the range of from 15 to 60% the soap level is substantially reduced. By this process the high-viscosity and separating-out problems attached to the soap emulsifier in the later stages of the reaction are avoided.

Acid catalyzed reactions

Abstract: Compositions containing sulfuric acid and one or more of certain chalcogen-containing compounds in which the chalcogen compound/H2 SO4 molar ratio is below 2 contain the mono-adduct of sulfuric acid which is catalytically active for promoting organic chemical reactions. Suitable chalcogen-containing compounds have the empirical formula ##STR1## wherein X is a chalcogen, each of R1 and R2 is independently selected from hydrogen, NR3 R4, and NR5, at least one of R1 and R2 is other than hydrogen, each of R3 and R4 is hydrogen or a monovalent organic radical, and R5 is a divalent organic radical. Such compositions are useful for catalyzing organic reactions such as oxidation, oxidative addition, reduction, reductive addition, esterification, transesterification, hydrogenation, isomerication (including racemization of optical isomers), alkylation, polymerization, demetallization of organometallics, nitration, Friedel-Crafts reactions, and hydrolysis. Novel catalysts are disclosed which involve combinations of the chalcogen compound-sulfuric compositions with one or more transition metal halides and/or with one or more surfactants. The surfactant-containing compositions are particularly useful for the treatment of materials containing lipophilic substances. Novel compositions containing a chalcogen compound-sulfuric acid component and one or more organic reactants are also disclosed.

Enzyme-catalyzed organic syntheses: transesterification reactions of chlorophyll a, bacteriochlorophyll a, and derivatives with chlorophyllase

Abstract: The green plant enzyme chlorophyllase (EC 3.1.1.14, chlorophyll chlorophyllido-hydroase) has been used for the synthesis of a variety of primary alcohol and diol esters of chlorophyll a, bacteriochlorophyll a, and pyrobacteriochlorophyll a. Green plant chlorophyllase accepts a much larger range of alcohol and chlorophyll substrates than had previously been realized. Thus, chlorophyllide and bacteriochlorophyllide esters of primary alcohols such as retinol and the detergent Triton X-100 and of dihydric alcohols such as ethylene glycol, butanediol, or 2-hydroxyethyl disulfide can readily be obtained by enzyme-assisted transesterification. The diol chlorophyllide esters are valuable intermediates for the synthesis of reaction center special pair models. Chlorophyllase-assisted reactions can be carried out in media containing up to 95% of organic solvents without the concomitant side reactions that important chlorophyll functional groups readily undergo even under mild conditions in conventional chemical synthetic procedures. In competitive chlorophyllase-catalyzed transesterification reactions, long-chain alcohols such as farnesol and retinol vs simple aliphatic alcohols and diols, the enzyme shows a definite preference for the long-chain alcohol. 37 references, 1 figure, 2 tables.

Isocyanate terminated quasi-prepolymers useful for preparing polyurethane/polyisocyanurate foams having low thermal conductivity

Abstract: Polyurethane/polyisocyanurate rigid foams having low thermal conductivity are prepared from isocyanate-terminated quasi-prepolymers prepared from polyester polyols derived from phthalic anhydride or from the transesterification of polyethylene terephthalate scrap.

Method for the enzymatic racemate resolution of racemic alcohols with/in vinyl esters by transesterification

Abstract: Racemic alcohols can be resolved in good yield and with high enantiomeric purity in the presence of vinyl esters with the aid of lipases from pig pancreas, pig liver and microorganisms.

Organotin-mediated synthesis of macrocyclic polyesters: mechanism and selectivity in the reaction of dioxastannolanes with diacyl dichlorides

Abstract: The reaction of 2,2-di-n-butyl-1,3,2-dioxastannolane with diacyl dichlorides for the synthesis of macrocyclic tetraesters has been investigated to gain an insight into its mechanistic pathway and to ascertain the occurrence of genuine template effects. Experimental results show unambiguously that the reaction is a clean cyclo-oligomerization involving a fast transesterification equilibrium that affords a thermodynamic distribution of oligomeric esters. No evidence to support a structural or ‘covalent’ template effect by tin was found. Instead, dioxastannolane is not only the reagent, but also behaves as an efficient transesterification catalyst that equilibrates the macrocyclic ester mixture. In this context, the reaction can hardly be considered selective.

Base catalyzed transesterification of vegetable oils 1

Abstract: Anhydrous methanolic sodium hydroxide catalyzed transesterification of vegetable oils yielded pure methyl esters within one minute at ambient temperature under nitrogen. Neither benzene nor phenolphthalein was required to maintain adequate stability of methanolic sodium hydroxide transesterification reagent. Additional esterification with methanolic HCl to convert free fatty acids to methyl esters was not required. Neutralization of excess base with 2.0 M HCl stopped saponification. Transesterification catalyzed by 1.0 M methanolic NaOH was reproducible and quantitative. Pentane and diethyl ether were excellent solvents for methanolic sodium hydroxide catalysis.

Limitations of Ambient Temperature Methods for the Methanolysis of Triacylglycerols in the Analysis of Fatty Acid Methyl Esters With High Accuracy and Reliability

Abstract: A comparison is presented of a method for the preparation of fatty acid methyl esters, involving hydroxide catalyzed transesterification at ambient temperature, with a second method employing methoxide catalyzed transesterification at reflux temperature. The first of these methods was specifically designed for the analysis of fats that contain very short chain length fatty acids (butyric and caproic acids), but it has been suggested that it might be suitable as a general method for the preparation of esters. It is now shown that the methoxide/reflux method gives more accurate results than does the hydroxide/ambient method when the samples to be analyzed contain high levels of long chain length fatty acids (e.g. stearic, palmitic, elaidic, oleic) and that it is quicker and at least as simple to carry out. The hydroxide/ambient method should be used only for its specific purpose and, when used, the procedure should be strictly followed and carefully standardized. Results obtained from fats that contain significant quantities of long chain length components should be viewed with suspicion.

Transesterification cure of thermosetting coatings

Abstract: A thermosetting paint coating composition is based on a thermosetting polymeric binder comprising a hydroxyl functional polyester polymer and a beta-hydroxy ester acrylic copolymer, where the polymer and copolymer are adapted to crosslink by transesterification in the presence of certain transesterification catalysts.

Lipase catalysis: Factors governing transesterification

Abstract: The use of enzymes in anhydrous organic solvents (Klibanov, 1986) makes it possible to carry out reactions like esterification, transesterification, etc. which are not possible in the presence of water. Lipases in particular are being successfully utilized for a wide range of regioselective esteritication of aiols (Hem~erle et al. 1987), sugars (Therisod et al. 1987) and in the resolution of alcohols like ~nthol (Langrand et al. 1986), sulcatol (StoKes et al. 1987), amino-butanol (Francalanci et al. 1987), etc.

Enzymatic transesterification with the lipase from Pseudomonas fragi 22.39 B in a non-aqueous reaction system.

Abstract: The lipase from Pseudomonas fragi 22.39 B catalyzed the transesterification in ester and alcohol mixtures without any other solvent. Activated esters, such as vinyl and phenyl esters, were excellent acyl donors for the reaction, and the activity was enhanced by increasing the carbon number of the fatty acid fraction of the esters. Primary alcohols were esterified faster than secondary ones in this reaction system, while tertiary alcohols such as alpha-terpineol did not react at all. The lipase exhibited stereoselectivity in the esterification of alcohols such as 2-octanol.

Process for the transesterification of fat and oil

Abstract: A process for the transesterification of substrates comprising (a) fat and oil and (b) one or more compounds selected from the group consisting of fatty acid, fatty acid ester and other fat and oil with the use of a lipase, wherein said transesterification is effected in the presence of a monohydric lower alcohol.

A Convenient Approach to the Synthesis of Deoxyribonucleoside-3′-hydrogen Phosphonates via Bis(1,1,1,3,3,3-hexafluoro-2-propyl) Phosphonate Intermediate

Abstract: Transesterification of a new reagent, bis(1,1,1,3,3,3-hexafluoro-2-propyl)phosphonates was found to be very effective for the preparation of deoxyribonucleoside-3′-hydrogen phosphonates. The yields of deoxyribooligonucleotides by the H-phosphonate method on a solid support depended on the molar concentrations of the reacting species.

Transesterification Reaction of Tetraethoxysilane and Butyl Alcohols

Abstract: Tetraethoxysilane was treated with Amberlyst 15 cation-exchange resin in the presence of butyl alcohols. On treating the mixture of tetraethoxysilane and 1-butanol, the transesterification took place in which butoxyl groups were substituted for ethoxyl groups in tetraethoxysilane. The degree of the transesterification depended on the molar ratio of tetraethoxysilane to 1-butanol of the mixture. The distribution of alkoxysilane species present in the tetraethoxysilane–1-butanol solution was compared with the tetrabutoxysilane–ethanol solution, and it was found that the degree of the transesterification depended on the ratio of numbers of alkyl groups in tetraalkoxysilane and alcohol used. The time required for equilibrium in the distribution of alkoxysilane species in the solution was different with the variety of butyl alcohols used, suggesting the presence of steric effect of butyl alcohols on this reaction.