Transesterification Of 1-phenylethanol Research Articles

Reaction kinetic studies on the immobilized-lipase catalyzed enzymatic resolution of 1-phenylethanol transesterification with ethyl butyrate

The enzyme-catalyzed transesterification reaction is an important route to realize the resolution of racemic optically active secondary alcohols. However, this route suffers from the high environment and engineering risks due to the usage of vinyl ester as acyl donor. In this work, an alternative acyl donor, ethyl butyrate, was used because it is more environment-friendly and catalyst-friendly. The kinetic studies on transesterification of 1-phenylethanol with ethyl butyrate catalyzed by immobilized-lipase Novozym™ 435 were carried out. The effects of agitation speed, reaction temperature, catalyst loading and initial molar ratio of reactants were investigated. The Ping-Pong-Bi-Bi and pseudo-homogeneous models were used to correlate the experimental data to estimate the kinetic parameters. The concentration-based Ping-Pong-Bi-Bi model was translated into its activity-based form to describe the non-ideality of the lipase-catalyzed reaction system. The activity-based Ping-Pong-Bi-Bi kinetic model performed best among all the models used.

The effect of the migrating group structure on enantioselectivity in lipase-catalyzed kinetic resolution of 1-phenylethanol

We have studied the effects of the acyl moiety on the enantioselectivity of three lipases: Candida antarctica B, Pseudomonas cepacia and Candida cylindracea, frequently used in kinetic resolutions by acylation or hydrolysis. The size of the acyl group was examined using various enol esters during the transesterification of 1-phenylethanol and the hydrolysis of the corresponding phenylethylesters. C. antarctica-B lipase showed the highest selectivity in the transesterification of 1-phenylethanol with isopropenyl and vinyl acetate, vinyl decanoate, vinyl laurate, (E > 200). The esters 1-phenyl -ethyl-acetate, decanoate and laurate are also hydrolyzed with high selectivities (E > 150) with CAL-B. The results can be correlated to the three-dimensional form of each lipase. The effect of the migrating group on the reactivity and selectivity of the lipases are discussed for both reactions. Nous avons étudié les effets du fragment acyle sur l'énantiosélectivité de trois lipases: Candida antarctica B, Pseudomonas cepacia et Candida cylindracea, fréquemment utilisées dans les dédoublements cinétiques par acylation ou hydrolyse. La taille du groupe acyle a été examinée en utilisant divers esters d'énols dans l'acylation du 1-phényléthanol et par hydrolyse des phenylethylesters correspondants. La lipase de C. antarctica-B a montré une haute sélectivité (E > 200) lors de la transestérification du 1-phényléthanol avec de l'acétate d'isopropényle, l'acétate de vinyle, le décanoate de vinyle, le laurate de vinyle. Avec cette lipase (CAL-B), les esters 1-phényl éthyl-acétate, décanoate et laurate sont hydrolysés avec des sélectivités élevées (E > 150). Les résultats peuvent être corrélés à la forme tridimensionnelle de chaque lipase. Pour les deux réactions, l'effet de la nature du groupe partant sur la réactivité et la sélectivité des lipases est discuté.

Highly basic catalysts obtained by intercalation of La-containing anionic complexes in layered double hydroxides

Nanocomposites have been obtained by intercalation of preformed negatively charged guest La hydroxy citrate colloids into host Mg/Al layered double hydroxides (LDH). These compounds have been used as precursors for La/Mg(Al)O mixed oxides catalysts. The La loading has been controlled by the colloids exchange rate in order to achieve a better dispersion of the lanthanum cations and thus improve the basic properties of the new catalysts. The increase of the d 0 0 3 interlayer distance from 0.830 nm in the host LDH to 1.196 nm in the nanocomposites shows that the intercalation has taken place leading to 1.82–11.16 wt% of lanthanum cation loadings. The basic properties of the La/Mg(Al)O( x) mixed oxides were evaluated qualitatively using Hammett indicators and quantitatively by TPD of CO 2. Both techniques indicated the presence of strong basic sites. The transesterification of 1-phenylethanol with diethylcarbonate (DEC), which is known to involve strong basic sites, was used to evaluate the catalytic activity of the La/Mg(Al)O( x) mixed oxides. Yields into carbonate product increase with the density of strong basic sites of the catalyst.

New basic catalysts obtained from layered double hydroxides nanocomposites

A new route for the preparation of basic mixed oxides using nanocomposite precursors obtained from layered double hydroxides (LDH) was investigated. These nanocomposites have been prepared by intercalation of negatively charged guest entities containing Ca 2+, Sr 2+, Ba 2+ or La 3+ cations in the interlayer space of host Mg/Al LDH by anionic exchange. The guest entities have been previously prepared by complexation of the required cations in the presence of edta or citrate chelating anions. Intercalation of [M n+(edta)] (4−n)− or [La(cit)OH] − complexes is proved by elemental analysis, XRD analysis and FT-IR spectroscopy. However, in order to satisfy the charge equilibrium in the materials, (edta) 4− and (citrate) 3− species are also co-intercalated in the nanocomposites. The basic properties of the mixed oxides obtained after thermal decomposition of the nanocomposites precursors were evaluated in the disproportionation of 2-methyl-3-butyn-2-ol (MBOH) and the transesterification of 1-phenylethanol with diethylcarbonate (DEC). The Sr- and Ba-containing mixed oxides exhibit basicity close to the one of MgO and Mg(La)O mixed oxides. A comparative study of the reactivity of La-containing mixed oxides obtained following different preparation routes, i.e. coprecipitation or anionic exchange, allows to conclude that the nanocomposite route led to the most active samples.

Enantioselective transesterification of racemic phenyl ethanol and its derivatives in organic solvent and ionic liquid using Pseudomonas aeruginosa lipase

The transesterification of 1-phenyl ethanol has been carried out using lipases from Pseudomonas aeruginosa MTCC 5113, to obtain chirally pure aryl ethanols with good yield and excellent enantioselectivity. The lipase from P. aeruginosa gave good conversion and moderate enantioselectivity (ee) in organic solvents, however, when the catalytic amount of ionic liquids were added in the reaction mixture, excellent enantioselectivity was obtained. Moreover, the change in enantiomer preference was seen in the presence of catalytic amount of ionic liquids. The findings revealed that hydrophobic ionic liquids (two-phase system) were the best solvents and 4-substituted aryl ethanols were the pre-eminent substrates for such type of reactions. The preparative scale (5 g) transesterification of 1-phenylethanol using lipases from P. aeruginosa yielded S-(−)-1-phenyl ethanol with 39% yield and >99% ee in hexane and 46% yield and >99% ee in [BMIm][PF 6].

Activity, stability and enantioselectivity of lipase-coated microcrystals of inorganic salts in organic solvents

Lipase-coated microcrystals of inorganic salts were prepared by dissolving enzymes in buffers and then mixing with 3 volumes of saturated salt solutions followed by drop-wise addition into polar precipitating organic solvents. The Mucor javanicus lipase-coated microcrystals did not show any activity for esterification of lauric acid with 1-propanol in isooctane when NaCl and Na2SO4 were used as the salts but showed much higher activity than the enzyme powder when KCl (10.0 times) and K2SO4 (5.8 times) were used as the salts and precipitated in 1-propanol. Acetonitrile was found to be the best precipitating solvent for preparing M. javanicus lipase-coated microcrystals, with enzyme activities 26.2 and 22.4 times higher than that of the enzyme powder when KCl and K2SO4 were used as precipitating salts, respectively. The presence of water in the precipitating solvents markedly decreased the enzyme activity. The M. javanicus lipase-coated microcrystals prepared using K2SO4 as the salt and acetonitrile as the precipitating solvent was as active at 80°C as at 40°C. No significant improvement in enantioselectivity of Candida rugosa lipase-coated microcrystals was observed for transesterification of 1-phenylethanol with vinyl acetate in hexane when the microcrystals were prepared by dissolving the enzymes in salt solutions containing 25% (v/v) of acetone or 2-propanol before precipitating in polar solvents.