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排序方式: 共有214条查询结果,搜索用时 15 毫秒
41.
研究了无水毗啶中酶催化棉子糖和丁二酸二乙烯酯、己二酸二乙烯酯、癸二酸二乙烯酯的酯交换反应,高选择性地合成了3种具有不同链长的可聚合的棉子糖乙烯酯.化合物经^1H NMR,^13C NMR和2D NMR表征,确证主要在棉子糖的β-呋喃果糖残基的C-1位OH上酯化.考察了7种不同来源的酶催化棉子糖酯合成的活性及温度、时间对反应的影响. 相似文献
42.
Mark W. Majewski 《Tetrahedron letters》2009,50(37):5175-5177
Diphenylammonium salts as catalysts for triglyceride transesterification have been investigated. Catalysts studied, such as diphenylammonium mesylate, were able to catalyze the transesterification process. Open atmosphere reactions and microwave-assisted reactions are considered and compared. Additionally, the study helps substantiate the advantage of microwave-assisted technology in organic synthesis. 相似文献
43.
Isabel Borreguero Jos V. Sinisterra Angel Rumbero Juan A. Hermoso Martín Martínez-Ripoll Andrs R. Alcntara 《Tetrahedron》1999,55(52):7231-14974
The regioselective acylation of phenylalkanediols catalysed by porcine pancreatic lipase (PPL) was the reaction used for modelling different areas in the active site of the enzyme. With this aim, different racemic or prochiral (1,n)-diols, with n ranging from 2 to 6 were resolved via transesterification with vinyl acetate, and the results were explained according to microcrystalline enzyme structure. Thus, we describe a logical model for explaining the enzyme regio and stereoselectivity, based on three residues of the active site (Ser153, Phe216 and His264) which turned out to be crucial for the substrate binding and transformation. 相似文献
44.
Dextrin is a polymer composed of α-(1→4) d-glucose units produced by partial hydrolysis of starch. In this work, the transesterification of the soluble polysaccharide with vinyl acrylate (VA) was carried out in anhydrous dimethylsulfoxide (DMSO). The effect of the water activity and of the enzyme Proleather, on the reaction rates, was analysed. Different degrees of substitution (DS) ranging from ca. 10% to 70% were obtained by controlling the molar ratio of VA to dextrin. Gels were obtained by free radical polymerization of dextrin-VA, with different degrees of substitution and monomer concentration, in water. A comprehensive solid state-NMR analysis of the hydrogels was performed. These hydrogels are being developed as scaffold materials for bioactive molecule and cell delivery, tissue engineering and a variety of other biomedical applications. 相似文献
45.
In biodiesel production, glycerol is formed as a side product and it is contained in the glycerol phase. This phase contains (besides glycerol): water, soaps, alcohol, traces of catalyst and glycerides and the remaining esters. In this paper, a new method for the determination of esters in the glycerol phase is introduced. The determination enables the minimization of the losses of biodiesel within the production process. It is based on the gradient RP-LC method (water and acetonitrile) with refractometric detection. The analysis is easy and the samples do not need any treatment (only dilution by water) and has a low detection limit. The results of this method were compared with the results of two other published methods: isocratic HPLC and GC. The disadvantage of these two methods is that they need extensive treatment of the sample, which takes many hours, and they are able to determine only the sum of esters. The new method is reliable, much faster and able to differentiate esters of almost each higher fatty acid (e.g. linoleic, linolenic, strearic alkyl ester) in the glycerol phase. 相似文献
46.
Shigeru Oae 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):79-113
Abstract Trimethyltelluroniumxanthogenates Me3TeS2CSR, -thioxanthogenates Me3TeS2CSR and -dithiocar-baates Me3TeS2CNR2 are obtained by reaction of Trimethyltelluroniumchlorid with sodiurnxanthogenates, -thioxanthogenates and -dithiocarbamates. Trimethyltelluroniurnxanthogenate Me3TeS2COR, -thioxanthogenate Me3TeS2CSR und -dithiocar-bamate Me3TeS2CNR2 werden durch Umsetzung von Trimethyltelluroniumchlorid mit den entspre-chenden Natriumxanthogenaten, -thioxanthogenaten und -dithiocarbarnaten erhalten. 相似文献
47.
In this present investigation, Cassia auriculata was explored as a feedstock for production of biodiesel. Transesterification reaction was performed by both enzyme (lipase) and chemical (potassium hydroxide) catalyst with diverse acyl acceptors such as methanol, ethanol, propanol, n-propanol, butanol, n- butanol, and finally their biodiesel yield were also recorded. Process optimization was performed by both one factor at a time method and response surface method. The maximal biodiesel yield of 92% (weight/weight) was obtained at the following optimal conditions: Oil:Methanol molar ratio of 1:6 (moles/moles), the lipase concentration of 2% (weight/weight), at 35 ?°C and 120 ?min. The highest biodiesel yield from Cassia auriculata oil was occurred with excess methanol that aids the equilibrium shift in the forward direction. The kinetics of the transesterification reaction was investigated under optimal conditions and the activation energy was found to be 14.91 ?kJ/mol. Simultaneously Gas Chromatography – Mass Spectroscopy was also carried out for the biodiesel produced from Cassia auriculata and the same has been reported. The GC analysis declares the existence of fatty acid esters like hexadecanoic acid methyl ester, methyl stearate and the peak with retention time 12.8 ?min signifies the evidence of hexadecanoic acid methyl ester with 28% of yield content. This investigation also evaluated the biodiesel quality produced from lipase-transesterified Cassia auriculata oil based on fuel properties. Biodiesel properties Flash Point (FC), Pour Point (PP) and kinematic viscosity were compared with American (ASTM 6751) and European (EN 14214) Standards. Cassia auriculata oil had PP 6.7 ?°C and Kinematic viscosity (813 ?kg/m3) that agreed with both the standards. Thus this study showed that Cassia auriculata oil could be a better fuel alternative with further improvement of fuel properties. 相似文献
48.
《Arabian Journal of Chemistry》2022,15(9):104074
Mo-KIT-6 catalysts precursors obtained by direct hydrothermal synthesis using different Si/Mo molar ratios (10, 20, 30) were evaluated in the production of biodiesel from the transesterification of soybean oil with methanol. A 22 + 3PtCt factorial design was used to evaluate the influence of alcohol/oil and Si/Mo ratios on biodiesel yield. ANOVA statistical analysis showed that Si/Mo ratio was the most significant variable. The factorial design showed that the optimal conditions for maximizing the biodiesel yield are: using the 10_Mo-KIT-6 catalyst, and an alcohol/oil ratio of 20/1 at 150 °C for 3 h. However, using the 20_Mo-KIT-6 catalyst with an alcohol/oil ratio of 15/1 the biodiesel yield is close to the maximum, having the advantage of using a lower amount of methanol, which means that the separation of non-reacted alcohol will consume less energy. 相似文献
49.
A high-purity sample of methyl phenyl carbonate (MPC) was obtained by developing a novel reaction route followed by a series
of separation and purification procedures. Identification and quantification of the MPC sample (98.32%) was performed by a
gas chromatography–mass spectrometry and Karl Fisher titration. The laboratory-prepared MPC was then used as a standard to
optimize quantitative analysis of the products synthesized by transesterification of dimethyl carbonate and phenol. The advantage
of the improved method was that MPC can be quantified directly rather than being calculated by subtracting the yield of diphenyl
carbonate (DPC) and by-product anisole from the conversion of dimethyl carbonate (DMC). The resulting method was validated
for linearity, precision, accuracy, detection limit, and quantification limit. With the improved method, simultaneous accurate
quantification of DMC, MPC, DPC, phenol, and anisole in the transesterification products can be achieved. This enables evaluation
of the activity and selectivity of different catalysts and control of the reaction processes.
相似文献
50.
Xiuhua Hao 《Tetrahedron letters》2004,45(4):781-785
Tin(IV) and hafnium(IV) bis(perfluorooctanesulfonyl)amide complexes were shown to give excellent yield and selectivity for highly practical transesterification and direct esterification, respectively, with an equimolar ratio of the reactants in a fluorous biphase system. It was found that these metal complexes were completely recovered and reused in the immobilized fluorous phase without loss of their catalytic activities. 相似文献