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Béla Török - One of the best experts on this subject based on the ideXlab platform.
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Synthesis of Chiral Trifluoromethyl Benzylamines by Heterogeneous Catalytic Reductive Amination
Topics in Catalysis, 2016Co-Authors: Sujaya Dasgupta, Elena Morzhina, Christian Schäfer, Shilpa C. Mhadgut, G. K. Surya Prakash, Béla TörökAbstract:The synthesis of several chiral α,α,α-trifluoromethylbenzylamines by an environmentally benign exclusively heterogeneous catalytic method is described. The procedure is based on trifluoromethyl acetophenones as starting materials. The commercially available inexpensive K-10 montmorillonite was applied for the synthesis of imines from the α,α,α-trifluoromethyl ketones and chiral α-methylbenzylamines. The diastereoselective Hydrogenations of the imines were carried out in the presence of 5 % Pd/BaCO_3 catalyst followed by the hydrogenolysis of the benzylic group under acidic conditions to give the respective chiral amines in good yields. The diastereomeric excess achieved in the Hydrogenation was further enhanced by a secondary kinetic resolution during the hydrogenolysis step ensuring good to excellent enantioselectivities. The simplicity of this method makes it an alternative synthetic procedure for the preparation of both enantiomers of substituted chiral α,α,α-trifluoromethylbenzylamines.
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Nature of Proline-induced Enantiodifferentiation in Asymmetric Pd Catalyzed Hydrogenations: Is the Catalyst Really Indifferent?
Catalysis Letters, 2008Co-Authors: Shilpa C. Mhadgut, Sujaya Dasgupta, Marianna Török, Béla TörökAbstract:The mode of enantioselection in the proline modified asymmetric Hydrogenation of isophorone (3,5,5-trimethyl-2-cyclohexenone) on supported Pd catalysts has been studied. It is shown that several experimental factors, such as modifier structure and chemical nature of the catalyst support, strongly affect the outcome of the Hydrogenations. Secondary kinetic resolution was found to be the major reason for obtaining high enantioselectivities on most catalysts. Extensive studies have been carried out to clarify the importance of the interaction of the proline–dihydroisophorone complex with the catalyst. The secondary kinetic resolution of dihydroisophorone was investigated under different conditions. First, racemic-dihydroisophorone was studied using several ( S )-proline modified supported Pd catalysts, then the individual enantiomers were subjected to a similar reaction on Pd/BaCO_3 catalyst in the presence of ( S )-proline. Our results provide convincing support for the heterogeneous enantioselection model under the current experimental conditions.
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APPLICATION OF CLAY CATALYSTS IN ORGANIC SYNTHESIS. A REVIEW
Organic Preparations and Procedures International, 2008Co-Authors: Sujaya Dasgupta, Béla TörökAbstract:INTRODUCTION 3 I. ACID CATALYSIS 4 1. Friedel-Crafts Reactions 4 a) Alkylation 4 b) Hydroxyalkylation 8 c) Acylation 8 2. Other Aromatic Electrophilic Substitutions 9 a) Nitration 9 b) Halogenation 12 c) Sulfonylation 13 3. Cycloaddition Reactions 13 4. Ring Opening-Ring Closure 14 5. Condensation 20 6. Protection-Deprotection Reactions 31 7. Rearrangements/Isomerization 35 8. Alkylation 42 9. Cyclopropanation 44 10. Aziridination 45 II. BASE CATALYSIS 46 1. Aldol Condensation 46 2. Knoevenagel Condensation 47 3. Rearrangements 47 III. OTHER SYNTHETIC APPROACHES BY MODIFIED CLAY CATALYSTS .........47 1. Hydrogenation-DeHydrogenation 48 a) Chemoselective Hydrogenations 48 ORGANIC PREPARATIONS AND PROCEDURES INT., 40 (1), 1-65 (2008)
Garry L. Rempel - One of the best experts on this subject based on the ideXlab platform.
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homogeneous Hydrogenation art of nitrile butadiene rubber a review
Polymer Reviews, 2013Co-Authors: Hui Wang, Lijuan Yang, Garry L. RempelAbstract:Hydrogenation of nitrile butadiene rubber (NBR) is an important research topic in the field of chemical modification of unsaturated polymers. This review provides an overview of the fundamental data, challenges, and recent advances in the research area of homogeneous Hydrogenation of NBR. Besides NBR and its Hydrogenation product HNBR, some other important elastomers such as styrene butadiene rubber (SBR), polybutadiene rubber (BR), polystyrene-b-polybutadiene-b-polystyrene (SBS block copolymer), and natural rubber (NR) were also involved for the related Hydrogenation reactions and characterization. A brief comparison of Hydrogenation catalysts including the heterogeneous and homogeneous catalysts was first conducted and the importance of rhodium (Rh) complex catalysts for homogeneous Hydrogenation of elastomers was addressed. This article continued to discuss the reaction pathways for realization of the homogeneous Hydrogenation of NBR. This was followed by an examination of the microstructures and chara...
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Hydrogenation of nitrile butadiene rubber in a multistage agitated contactor: Experiments and numerical simulation
Chemical Engineering Science, 2010Co-Authors: Lifeng Zhang, Garry L. RempelAbstract:The performance of a multistage agitated contactor (MAC) with cocurrent reactive gas liquid upflow was studied for the Hydrogenation of nitrile butadiene rubber using a homogenous osmium complex catalyst. The Hydrogenation performance was investigated under various catalyst concentrations, liquid flow rates, pressures, and polymer concentrations. The desirable Hydrogenation conversion of over 95% was achieved under the industrially relevant operation conditions. A comprehensive reactor model consisting of stirred tanks in series with back flow (CTB) was applied to describe the liquid flow behaviour in the presence of the Hydrogenation process. The established model satisfactorily predicted dynamic Hydrogenation performance considering the gas liquid mass transfer effect and temperature profile in each stage. A modified CSTRs-in-series model accounting for mass transfer effect was proposed to predict the Hydrogenation degree at steady state and a good agreement was demonstrated between the model prediction and the experimental data.
Sujaya Dasgupta - One of the best experts on this subject based on the ideXlab platform.
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Synthesis of Chiral Trifluoromethyl Benzylamines by Heterogeneous Catalytic Reductive Amination
Topics in Catalysis, 2016Co-Authors: Sujaya Dasgupta, Elena Morzhina, Christian Schäfer, Shilpa C. Mhadgut, G. K. Surya Prakash, Béla TörökAbstract:The synthesis of several chiral α,α,α-trifluoromethylbenzylamines by an environmentally benign exclusively heterogeneous catalytic method is described. The procedure is based on trifluoromethyl acetophenones as starting materials. The commercially available inexpensive K-10 montmorillonite was applied for the synthesis of imines from the α,α,α-trifluoromethyl ketones and chiral α-methylbenzylamines. The diastereoselective Hydrogenations of the imines were carried out in the presence of 5 % Pd/BaCO_3 catalyst followed by the hydrogenolysis of the benzylic group under acidic conditions to give the respective chiral amines in good yields. The diastereomeric excess achieved in the Hydrogenation was further enhanced by a secondary kinetic resolution during the hydrogenolysis step ensuring good to excellent enantioselectivities. The simplicity of this method makes it an alternative synthetic procedure for the preparation of both enantiomers of substituted chiral α,α,α-trifluoromethylbenzylamines.
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Nature of Proline-induced Enantiodifferentiation in Asymmetric Pd Catalyzed Hydrogenations: Is the Catalyst Really Indifferent?
Catalysis Letters, 2008Co-Authors: Shilpa C. Mhadgut, Sujaya Dasgupta, Marianna Török, Béla TörökAbstract:The mode of enantioselection in the proline modified asymmetric Hydrogenation of isophorone (3,5,5-trimethyl-2-cyclohexenone) on supported Pd catalysts has been studied. It is shown that several experimental factors, such as modifier structure and chemical nature of the catalyst support, strongly affect the outcome of the Hydrogenations. Secondary kinetic resolution was found to be the major reason for obtaining high enantioselectivities on most catalysts. Extensive studies have been carried out to clarify the importance of the interaction of the proline–dihydroisophorone complex with the catalyst. The secondary kinetic resolution of dihydroisophorone was investigated under different conditions. First, racemic-dihydroisophorone was studied using several ( S )-proline modified supported Pd catalysts, then the individual enantiomers were subjected to a similar reaction on Pd/BaCO_3 catalyst in the presence of ( S )-proline. Our results provide convincing support for the heterogeneous enantioselection model under the current experimental conditions.
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APPLICATION OF CLAY CATALYSTS IN ORGANIC SYNTHESIS. A REVIEW
Organic Preparations and Procedures International, 2008Co-Authors: Sujaya Dasgupta, Béla TörökAbstract:INTRODUCTION 3 I. ACID CATALYSIS 4 1. Friedel-Crafts Reactions 4 a) Alkylation 4 b) Hydroxyalkylation 8 c) Acylation 8 2. Other Aromatic Electrophilic Substitutions 9 a) Nitration 9 b) Halogenation 12 c) Sulfonylation 13 3. Cycloaddition Reactions 13 4. Ring Opening-Ring Closure 14 5. Condensation 20 6. Protection-Deprotection Reactions 31 7. Rearrangements/Isomerization 35 8. Alkylation 42 9. Cyclopropanation 44 10. Aziridination 45 II. BASE CATALYSIS 46 1. Aldol Condensation 46 2. Knoevenagel Condensation 47 3. Rearrangements 47 III. OTHER SYNTHETIC APPROACHES BY MODIFIED CLAY CATALYSTS .........47 1. Hydrogenation-DeHydrogenation 48 a) Chemoselective Hydrogenations 48 ORGANIC PREPARATIONS AND PROCEDURES INT., 40 (1), 1-65 (2008)
Javier Perezramirez - One of the best experts on this subject based on the ideXlab platform.
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from the lindlar catalyst to supported ligand modified palladium nanoparticles selectivity patterns and accessibility constraints in the continuous flow three phase Hydrogenation of acetylenic compounds
Chemistry: A European Journal, 2014Co-Authors: Gianvito Vile, Neyvis Almorabarrios, Sharon Mitchell, Nuria Lopez, Javier PerezramirezAbstract:Site modification and isolation through selective poisoning comprise an effective strategy to enhance the selectivity of palladium catalysts in the partial Hydrogenation of triple bonds in acetylenic compounds. The recent emergence of supported hybrid materials matching the stereo- and chemoselectivity of the classical Lindlar catalyst holds promise to revolutionize palladium-catalyzed Hydrogenations, and will benefit from an in-depth understanding of these new materials. In this work, we compare the performance of bare, lead-poisoned, and ligand-modified palladium catalysts in the Hydrogenation of diverse alkynes. Catalytic tests, conducted in a continuous-flow three-phase reactor, coupled with theoretical calculations and characterization methods, enable elucidation of the structural origins of the observed selectivity patterns. Distinctions in the catalytic performance are correlated with the relative accessibility of the active site to the organic substrate, and with the adsorption configuration and strength, depending on the ensemble size and surface potentials. This explains the role of the ligand in the colloidally prepared catalysts in promoting superior performance in the Hydrogenation of terminal and internal alkynes, and short-chain alkynols. In contrast, the greater accessibility of the active surface of the Pd-Pb alloy and the absence of polar groups are shown to be favorable in the conversion of alkynes containing long aliphatic chains and/or ketone groups. These findings provide detailed insights for the advanced design of supported nanostructured catalysts. Hybrid nanocatalysts: The classical Lindlar and the newly developed NanoSelectTM catalysts are confronted in the semi-Hydrogenation of alkynes (see figure). Systematic testing under continuous-flow three-phase conditions, coupled with detailed characterization analyses and molecular simulations, enable the understanding of the structure of the catalysts and the associated activity and selectivity patterns for a wide range of acetylenic compounds.
Klavs F Jensen - One of the best experts on this subject based on the ideXlab platform.
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scalable thin layer membrane reactor for heterogeneous and homogeneous catalytic gas liquid reactions
Green Chemistry, 2018Co-Authors: Yiming Mo, Joseph Imbrogno, Haomiao Zhang, Klavs F JensenAbstract:Catalytic gas–liquid reactions have potential as environmentally benign methods for organic synthesis, particularly Hydrogenation and oxidation reactions. However, safety and scalability are concerns in the application of gas–liquid reactions. In this work, we develop and demonstrate a scalable, sustainable, and safe thin-layer membrane reactor for heterogeneous Pd-catalyzed Hydrogenations and homogenous Cu(I)/TEMPO alcohol oxidations. The implementation of a Teflon amorphous fluoroplastic (AF) membrane and porous carbon cloth in the membrane reactor provides sufficient gas–liquid mass transfer to afford superior performance compared to conventional packed-bed or trickle-bed reactors. The membrane separates the gas from the liquid, which avoids the formation of explosive mixtures for oxygenation reactions and simplifies the two-phase hydrodynamics to facilitate scale-up by stacking modules, while significantly reducing gas consumption. In addition, 3-dimensional simulations deliver insights into the mass transfer and hydrodynamic behavior to inform optimal membrane reactor design and operation.
