Enantioselective Hydrogenation Of Ethyl Pyruvate Research Articles

Restructuring Effects in the Platinum-Catalysed Enantioselective Hydrogenation of Ethyl Pyruvate

Restructuring Effects in the Platinum-Catalysed Enantioselective Hydrogenation of Ethyl Pyruvate

Mesoporous silica-supported Pt catalysts in enantioselective hydrogenation of ethyl pyruvate

Catalytic properties of Pt catalysts supported on mesoporous silica (Pt/m-SiO2) have been studied in enantioselective hydrogenation of ethyl pyruvate. The influences of pore structure of mesoporous silica (m-SiO2), type of chiral modifier, and H2 pressure on the catalytic performance have been investigated by using various m-SiO2 supports and cinchona alkaloids and by varying H2 pressure. The use of MCM-41, SBA-15, KIT-6, and MCF reveals that characteristic pore structure and size of m-SiO2 supports significantly affect both activity and enantioselectivity. A facile diffusion of chiral modifier through large mesopores of MCF support enables Pt/MCF to exhibit excellent performance. A comparison of the efficiency of cinchona alkaloids-modified Pt catalysts shows that QN and QD lead to higher performance than CD and CN at ambient H2 pressure. The influence of cinchona alkaloids on enantioselectivity noticeably depends on H2 pressure. Cinchona alkaloid-modified Pt/m-SiO2 exhibit superior enantioselectivity to the corresponding Pt/Al2O3 under various H2 pressures. These results imply that m-SiO2 is a promising support and that fine control of pore structure can further improve catalytic performance of Pt/m-SiO2 in heterogeneous enantioselective hydrogenation.

Platinum nanoparticles supported on mesocellular silica foams as highly efficient catalysts for enantioselective hydrogenation

Mesocellular silica foams (MCFs) with different pore size were synthesized and used as supports for Pt catalysts for enantioselective hydrogenation of ethyl pyruvate. The influences of the pore size of MCFs, the amount of Pt loading and H2 pressure on catalytic performance of cinchonidine-modified Pt/MCFs were investigated. Both activity and enantioselectivity of the Pt/MCF catalyst increased with the increase in the pore size. These results were attributed to the fact that the larger mesopores facilitate intraparticle diffusion of bulky chiral modifier molecules and generate more chirally modified Pt sites. The performances of Pt/MCFs were compared to those of Pt supported on non-porous silica (Pt/SiO2) and commercial Pt/Al2O3 catalysts. The 1 wt% Pt/MCFs showed superior performance than the 1 wt% Pt/SiO2 and the commercial 1 wt% Pt/Al2O3 catalysts. Furthermore, the 0.6 wt% Pt/MCF exhibited higher activity and enantioselectivity than the commercial 5 wt% Pt/Al2O3, one of the most efficient heterogeneous catalysts for this reaction, in spite of a considerably less Pt loading. At optimized reaction conditions, the Pt/MCF catalyst gave enantiomeric excess of 96% at 100% conversion. They also maintained high enantioselectivity during 10 successive reaction cycles, exhibiting high reusability.

New Strategies in Enantioselective Hydrogenation on Supported Transition Metal Catalyst: Effects of Metal Sintering and Support Swelling

The effect of noble metal catalysts supported on an ionic exchange resin for the enantioselective hydrogenation of ethyl pyruvate to ethyl lactate was studied. High activity and moderate enantioselectivity levels were obtained. Pt was the best enantioselective metallic phase, followed by Pd and Au; Rh was the less enantioselective metallic phase. The effect of the active site was evaluated for the most enantioselective catalyst: 2Pt-WA30 (prefix indicates the metal loading). A novel method for sintering the Pt metal particles by nitriles reduction was used, and a controlled migration of the metal particles to the surface layers was observed. There existed an optimal particle size with maximization of the enantiomeric excess, corresponding to 24 h sintering. The hydrogenation of ethyl pyruvate to ethyl lactate was found to be structure-sensitive and the importance of the metal particle size for the adsorption of the chiral modifier was proved. Two different chirality induction methods were tried for the 2Pt-WA30 catalyst: (i) the addition of the chiral modifier (CM) to the reaction media, or (ii) the modification of the catalyst in a swelling medium prior to the reaction in order to encapsulate CM. Lower activity but higher enantioselectivity levels were obtained with method (ii). Finally, the reuse of the catalysts was also assessed by means of consecutive reaction tests.

Effective and durable Pt nanocatalyst supported on three-dimensionally ordered macroporous carbon for asymmetric hydrogenation

Pt nanoparticles supported on three-dimensionally ordered macroporous carbon (Pt/3DC) were prepared and applied as catalyst after chirally modified with cinchonidine for the enantioselective hydrogenation of ethyl pyruvate. The catalyst was characterized by SEM, TEM, powder XRD, N2 sorption, and CO chemisorption, which confirmed the well-defined periodic macroporous structure of Pt/3DC and the high dispersion of Pt nanoparticles on the support. High catalytic performance was achieved over chirally modified Pt/3DC catalyst in the asymmetric hydrogenation of ethyl pyruvate. A high turnover frequency of 11,800h−1 with an enantiomeric excess of 79.5% was acquired in acetic acid. In particular, this catalyst exhibited high durability in the asymmetric hydrogenation system and could be easily reused at least 13 times with well-maintained catalytic activity and slightly decreased enantioselectivity. Moreover, the comparison of catalytic performance between Pt/3DC and commercial Pt/C as well as Pt/Al2O3 was carried out.

Experimental and theoretical investigation of the enantioselective hydrogenation of ethyl pyruvate with a Pt catalyst with new non-cinchona chiral modifiers

The enantioselective hydrogenation of ethyl pyruvate using a Pt/SiO2 catalyst modified with six different chiral modifiers was studied. The chiral modifiers chosen were: (S)-(+)-1-aminoindan, (R)-(−)-1-aminoindan, (1R,2S)-(+)-cis-1- amino-2-indanol, (1S,2R)-(−)-cis-1-amino-2-indanol, (S)-(+)-1-indanol and (R)-(−)-1-indanol.An excess of the (R) enantiomer of the product of 63% and 45% with (S)-(+)-1-aminoindan and (R)-(−)-1-aminoindan modifiers, respectively was obtained. When using (1S,2R)-(−)-cis-1-amino-2-indanol and (1R,2S)-(+)-cis-1-amino-2-indanol, the enantiomeric excess (ee%) obtained was 30% and 5%, respectively, while with both indanols ee% did not exceed 8%. Molecular modeling of the complex formed between the chiral modifier and ethyl pyruvate performed by DFT calculations allowed predicting the values of ee% obtained experimentally. The low ee% value obtained both aminoindanol chiral modifiers were used, could be explained by the analysis of non-covalent interactions (NCI) method. These calculations demonstrated the presence of an intramolecular hydrogen bond in the structure of these modifiers.

Enantioselective Hydrogenation of Ethyl Pyruvate Catalyzed by 1,2-Diphenyl-ethylenediamine-Modified Iridium Complex: Effect of Solvent

Enantioselective Hydrogenation of Ethyl Pyruvate Catalyzed by 1,2-Diphenyl-ethylenediamine-Modified Iridium Complex: Effect of Solvent

Structural properties of alumina- and silica-supported Iridium catalysts and their behavior in the enantioselective hydrogenation of ethyl pyruvate

Iridium catalysts were prepared using alumina or silica as supports and two preparation methods, incipient wetness impregnation and flame spray pyrolysis. These catalysts were characterized, after reduction in hydrogen, by transmission electron microscopy, infrared spectroscopy of adsorbed CO and microcalorimetry of CO chemisorption. Aliquots of these catalysts were tested in the ethyl pyruvate hydrogenation using cinchonidine as a chiral modifier. Different enantioselectivities to (R)-ethyl lactate were obtained depending on the support material and the preparation method. Based on the structural characterization it is proposed that the different enantioselectivities are mainly due to different surface structure of the iridium nanoparticles caused by the support interaction.

Physicochemical study of polymer-stabilized platinum catalysts for enantioselective hydrogenation of ketones

Platinum-containing catalytic systems based on hyper-cross-linked polystyrene have been synthesized, and their structure has been investigated. The catalysts have been tested in the enantioselective hydrogenation of ethyl pyruvate as a model reaction. The product of this reaction—(R)-ethyl lactate—is usable as a chiral monomer in the synthesis of biodegradable polymers. The catalytic systems have been characterized by XPS, TEM, X-ray diffraction, diffuse reflectance IR spectroscopy, and low-temperature nitrogen adsorption. The formation of Pt(0) particles in the polymer matrix begins at the precursor introduction stage. The resulting active phase particles have a narrow size distribution with a peak occurring at 2 nm. The maximum enantiomeric excess attained in the test reaction is 75%. It is possible to premodify the catalyst without lowering the enantioselectivity of the hydrogenation process.

Influence of achiral amine additives on the Orito's reaction

In enantioselective hydrogenation of ethyl pyruvate and methylbenzoyl formate over Pt/Al2O3 catalyst achiral tertiary and secondary amine additives increased both the reaction rate and the enantiomeric excess using low cinchonidine concentration and toluene as a solvent. However, no beneficial effect of primary amine was observed. Results of circular dichroism spectroscopic measurements proved that in the presence of both secondary and tertiary amines the virtual concentration of chiral modifier increased in accordance with the shift of dimer–monomer equilibrium of cinchonidine. The effect of achiral amines was more pronounced at ethyl pyruvate than at methylbenzoyl formate substrate.

Synthesis and Application of Polystyrene Nanospheres Supported Platinum Catalysts in Enantioselective Hydrogenations

Nearly monodisperse polystyrene nanospheres coated with platinum have been synthesized and applied successfully in the cinchona alkaloid-modified enantioselective hydrogenation of ethyl pyruvate. During the catalyst preparation broadly varied experimental conditions were used resulting in several catalysts with different properties. The effect of hydrogen pressure, solvent, modifier and polystyrene nanoparticle size on the enantioselectivity was also studied. Based on the results the effect of support on the mechanism of the enantiodifferentiation has been discussed.

Pore Structure and Surface Acidity Effects of Ordered Mesoporous Supports on Enantioselective Hydrogenation of Ethyl Pyruvate

AbstractThe enantioselective hydrogenation of ethyl pyruvate is studied using cinchonidine‐modified platinum supported on ordered mesoporous materials as a catalyst. The influence of different pore structures and hence, textural properties of the support on the enantiodifferentiation is investigated. The selected representative model supports are SBA‐15, SBA‐16, and KIT‐6. Depending on the pore structure, varying enantioselectivities are obtained. Furthermore, SBA‐15 is post‐synthetically aluminated to produce materials with different Si/Al ratios. An increase in Al content leads to an increased support surface acidity and enhanced enantioselectivity. The catalyst samples are characterized by small‐angle X‐ray scattering (SAXS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature‐programmed desorption of ammonia (TPAD), and N2 and CO sorption techniques. Applying optimized reaction conditions resulted in enantiomeric excesses of (R)‐ethyl lactate of 90–94 % ee at total conversion.

An easy and effective approach towards heterogeneous Pt/SiO 2-cinchonidine catalyst system for enantioselective hydrogenation of ethyl pyruvate

A single unit catalyst system (Pt/silica–chiral modifier) is developed for the enantioselective hydrogenation of ethyl pyruvate. Cinchonidine was tethered directly without prior modification over carboxylate functionalized SBA-15 by the reaction of vinyl group in cinchonidine with –COOH group in functionalized SBA-15 through ester linkage. Then Pt nanoparticles were deposited over cinchonidine tethered SBA-15. The mesostructures were characterized by small-angle XRD, N 2 sorption and TEM, while the surface functionalization was confirmed by FTIR, TG/DTA and solid state 13C NMR. Enantioselectivity of the catalyst system for hydrogenation of ethyl pyruvate was determined by GC/FID. The highest enantiomeric excess was achieved as 70.8% and the catalyst recyclability was authenticated even after 3rd reuse without significant loss in enantiomeric excess.

ChemInform Abstract: Enantioselective Hydrogenation of Ethyl Pyruvate.

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Pt Nanoparticles Supported on Highly Dispersed Alumina Coated inside SBA‐15 for Enantioselective Hydrogenation

AbstractA series of Al2O3@SBA‐15 composites with different alumina loadings have been prepared using a solid‐state grinding method. Various techniques, such as X‐ray diffraction, N2 sorption, FT‐IR spectroscopy, and NMR spectroscopy, are used to characterize their structures and acidity. The Al2O3@SBA‐15 composites retain the mesostructure of the SBA‐15 host and the alumina is highly dispersed and uniformly coated inside the mesopores. The Al2O3@SBA‐15 composites serve as remarkable supports for Pt nanoparticles, which can be used as catalysts in the enantioselective hydrogenation of ethyl pyruvate. Both the Brønsted acid sites that originate from the interface of Al2O3 and SBA‐15 in the Al2O3@SBA‐15 composites and the appropriate interaction of Pt nanoparticles with alumina coated inside the mesopores of SBA‐15 can improve the catalytic behavior of Pt/Al2O3@SBA‐15 catalysts.

Dendritic Core–Multishell Polymer Templates for the Synthesis of Pt Nanoparticle‐Loaded Porous Silica and their Application as Catalysts for the Enantioselective Hydrogenation of Ethyl Pyruvate

Dendritic Core–Multishell Polymer Templates for the Synthesis of Pt Nanoparticle‐Loaded Porous Silica and their Application as Catalysts for the Enantioselective Hydrogenation of Ethyl Pyruvate

Enantioselective hydrogenation of ethyl pyruvate and 1-phenyl-1,2-propanedione on catalysts prepared by impregnation of colloidal platinum on SiO2

The enantioselective hydrogenation of ethyl pyruvate and 1-phenyl-1,2-propanedione was studied at 298 K and 40 bar of H2 over colloidal Pt stabilized with cinchonidine (CD) and supported on silica. The catalysts were prepared by impregnation of colloidal Pt on SiO2, leading to a metal load close to 1 wt.%. The colloid was prepared from an aqueous solution of H2PtCl6 and stabilized with different quantities of CD. The catalysts were characterized by nitrogen adsorption-desorption isotherms at 77 K, XPS, XRD and TEM techniques. The reactions were carried out in a stainless steel batch reactor using cyclohexane as solvent and cinchonidine as chiral modifier. The addition of CD to the catalysts allows the stabilization and control of the platinum particle size and also affects the enantiomeric excess (ee) of the system, affording a higher proportion of the (R)-product. The relationship between the enantioselectivity and the CD concentration (added in situ) exhibits a bell type curve for both reactions, this being indicative of the importance of a competitive adsorption of the modifier and substrate on the catalyst surface.

New data in the enantioselective hydrogenation of ethyl pyruvate on Pt-cinchona chiral catalyst using continuous-flow fixed-bed reactor system: The origin of rate enhancement

The origin of rate enhancement in the enantioselective heterogeneous catalytic hydrogenation of ethyl pyruvate on Pt modified with the parent cinchonas, as compared to the unmodified Pt, was studied in a solvent mixture toluene/AcOH 9/1. Hydrogenation experiments were carried out in a continuous-flow fixed-bed reactor and in several cases for comparison in batch reactors over E4759 catalyst. Our results obtained using a novel procedure, namely racemic hydrogenation followed by three changes of the chiral modifier (on the same catalyst) supported an intrinsic “ligand acceleration” character of the rate enhancement in ethyl pyruvate hydrogenation.

ENANTIOSELECTIVE HYDROGENATION OF ETHYL PYRUVATE IN FLOW REACTOR OVERPt-CD/Si0(2) CATALYSTS

ABSTRACT The continuous enantioselective hydrogenation of ethyl pyruvate (EP) in a continuous flow reactor at 25oC on 1%Pt-CD/SiO 2 catalysts has been studied. The catalytic study included the analysis of variables such as: particle size, feed flow, H 2 pressure and the addition of chiral modifier to the reactor feed. The catalysts were prepared using impregnation of Pt colloids which are stabilized with different quantities of cinchonidine (CD) on SiO 2 . This process gives chiral properties to the catalyst and allows changing the particle size for the reaction of interest. The catalysts were characterized by adsorption/desorption isotherms of N 2 a 77 K, TEM, XPS and the analysis of products by GC-MS. The monitoring of the reaction indicates a significant increases in the conversion when decreasing the contact time and a maximum in the enantiomeric excess (ee) of 63 % to the (R)-ethyl lactate which is obtained after using 200mg of 1%Pt/SiO 2 catalyst (1.6nm) at 10 bar of H 2 and a flow of 0.3 mL/min of a mixture EP (0.01M) and CD (0.034M) in cyclohexane.Keywords: Continuous hydrogenation, Nanoparticles, Platinum, Ethyl Pyruvate, Cinchonidine. e-mail: doruiz@udec.cl, preyes@udec.cl

New Data on the Orito Reaction: Effect of Substrate Structure on Nonlinear Phenomenon

The nonlinear phenomenon (NLP) was studied for the first time in the enantioselective hydrogenation of ethyl pyruvate (EP) and ketopantolactone (KPL) under identical conditions, on Pt catalyst modified by quinine and cinchonine, and for comparison with cinchonidine-cinchonine pair. The data obtained using the three methods allowed recognition of a new observation, namely that the NLP depends not only on the chiral modifier but also on the substrate to be hydrogenated. This observation can presumably be interpreted on the basis of differences in the structure of the substrate-modifier complexes formed and in the adsorption-desorption processes of the complexes, thus the NLP is not solely dependent on the adsorption of cinchona alkaloids, as suggested by earlier experimental data.