Amine Catalyst Research Articles

Catalytic amination of 1,6-hexanediol for synthesis of N, N, N’, N’-tetramethyl-1,6-hexanediamine over Cu/Ni/Zn catalysts

Synthesis of N, N, N’, N’-tetramethyl-1,6-hexanediamine(TMHDA) by the amination of 1,6-hexanediol(HDO) and dimethylamine(DMA) at normal pressure over an outstanding Cu/Ni/Zn catalyst supported on aluminum oxide(γ-Al2O3) was studied in this article. Cu/Ni/Zn/γ-Al2O3(Cu: Ni: Zn = 28: 7: 12) exhibited excellent catalytic performance, which HDO was almost completely transformed and TMHDA reached 85 % selectivity at 200 °C. The amination of HDO required two hydrogenations and two dehydrogenations, and the selectivity of the amination catalyst depended on the balance of dehydrogenation and hydrogenation. Various characterization (TEM, BET, XRD, H2-TPR, XPS) demonstrated that the addition of Zn to the Cu/Ni catalyst could reduce the agglomeration of Cu/Ni particles and change the valence distribution of Cu. The Cu/Ni/Zn/γ-Al2O3 catalyst was a very promising and green method for the synthesis of tertiary diamines through amination of diols.

Comparative Review for Enhancing CO2 Capture Efficiency with Mixed Amine Systems and Catalysts.

This study investigates methods to enhance the efficiency of CO2 capture using organic amine absorption and compares the performance of traditional and novel amine solvents. It reviews various single-component and mixed amine absorbents, as well as catalysts used in these methods, highlighting the superiority of mixed amine absorbents over single-component amine absorbents in CO2 absorption and desorption. Additionally, the study explores the catalytic mechanisms and effects of catalysts in the CO2 absorption/desorption process with amine solvents and provides an outlook on future research directions. The aim is to promote the widespread adoption of organic amine absorption technology in industrial applications and to contribute to the development of more sustainable and efficient CO2 capture technologies.

Thermally-stable single-site Pd on CeO2 catalyst for selective amination of phenols to aromatic amines without external hydrogen.

Developing a new route to produce aromatic amines as key chemicals from renewable phenols is a benign alternative to current fossil-based routes like nitroaromatic hydrogenation, but is challenging because of the high dissociation energy of the Ar-OH bond and difficulty in controlling side reactions. Herein, an aerosolizing-pyrolysis strategy was developed to prepare high-density single-site cationic Pd species immobilized on CeO2 (Pd1/CeO2) with excellent sintering resistance. The obtained Pd1/CeO2 catalysts achieved remarkable selectivity of important aromatic amines (yield up to 76.2%) in the phenols amination with amines without external hydrogen sources, while Pd nano-catalysts mainly afforded phenyl-ring-saturation products. The excellent catalytic properties of the Pd1/CeO2 are closely related to high-loading Pd single-site catalysts with abundant surface defect sites and suitable acid-base properties. This report provides a sustainable route for producing aromatic amines from renewable feedstocks.

Thermally‐stable single‐site Pd on CeO2 catalyst for selective amination of phenols to aromatic amines without external hydrogen

Developing a new route to produce aromatic amines as key chemicals from renewable phenols is a benign alternative to current fossil‐based routes like nitroaromatic hydrogenation, but is challenging because of the high dissociation energy of the Ar‐OH bond and difficulty in controlling side reactions. Herein, an aerosolizing‐pyrolysis strategy was developed to prepare high‐density single‐site cationic Pd species immobilized on CeO2 (Pd1/CeO2) with excellent sintering resistance. The obtained Pd1/CeO2 catalysts achieved remarkable selectivity of important aromatic amines (yield up to 76.2%) in the phenols amination with amines without external hydrogen sources, while Pd nano‐catalysts mainly afforded phenyl‐ring‐saturation products. The excellent catalytic properties of the Pd1/CeO2 are closely related to high‐loading Pd single‐site catalysts with abundant surface defect sites and suitable acid‐base properties. This report provides a sustainable route for producing aromatic amines from renewable feedstocks.

High-Throughput Screening and Prediction of Nucleophilicity of Amines Using Machine Learning and DFT Calculations.

Nucleophilic index (NNu) as a significant parameter plays a crucial role in screening of amine catalysts. Indeed, the quantity and variety of amines are extensive. However, only limited amines exhibit an NNu value exceeding 4.0 eV, rendering them potential nucleophiles in chemical reactions. To address this issue, we proposed a computational method to quickly identify amines with high NNu values by using Machine Learning (ML) and high-throughput Density Functional Theory (DFT) calculations. Our approach commenced by training ML models and the exploration of Molecular Fingerprint methods as well as the development of quantitative structure-activity relationship (QSAR) models for the well-known amines based on NNu values derived from DFT calculations. Utilizing explainable Shapley Additive Explanation plots, we were able to determine the five critical substructures that significantly impact the NNu values of amine. The aforementioned conclusion can be applied to produce and cultivate 4920 novel hypothetical amines with high NNu values. The QSAR models were employed to predict the NNu values of 259 well-known and 4920 hypothetical amines, resulting in the identification of five novel hypothetical amines with exceptional NNu values (>4.55 eV). The enhanced NNu values of these novel amines were validated by DFT calculations. One novel hypothetical amine, H1, exhibits an unprecedentedly high NNu value of 5.36 eV, surpassing the maximum value (5.35 eV) observed in well-established amines. Our research strategy efficiently accelerates the discovery of the high nucleophilicity of amines using ML predictions, as well as the DFT calculations.

Proline-based Organocatalyst for the Synthesis of Arylidene Benzofuranone Intermediates Enabling the Construction of Aurone-derived Azadienes

Organocatalysis has been recognized as a part of chemical research for a long time, and it gained significant attention in catalysis in recent decades. Amine catalyst is a substantial type of organocatalysis, and it is successively employed for the activation of carbonyl compounds. This manuscript delves into the exploration of a proline-based organocatalyst for the synthesis of arylidene benzofuranone intermediates, a critical step that facilitates the subsequent construction of aurone-derived azadienes. In this work, we successfully reported the synthesis of arylidene benzofuranone intermediates through Aldol condensation of benzofuranone with different aldehydes enabled by proline-derived organic catalysts. To achieve this strategy, six examples of amine organocatalysts (A1-A6) were evaluated to showcase the optimal catalyst for this transformation. Moreover, the arylidene benzofuranone intermediates were further employed for the synthesis of interesting aurone-derived azadiene substrates through its reaction with TsNH2. Notably, the using of organocatalyst A6 resulted in the delivery of the product with the best yield (94% isolated yield). Under the optimized conditions, different aromatic and heterocyclic containing aldehydes were effectively tolerated to generate the corresponding arylidene benzofuranone intermediates, which further converted to the azadiene products in high to excellent yield. The claimed structures were confirmed by the spectral analysis.

Direct amination of toluene with hydroxylamine to produce toluidine over vanadium catalysts

In this study, metallic vanadium was used as catalysts for direct amination of toluene with hydroxylamine to produce toluidine under mild conditions. High toluene conversion and toluidine selectivity were obtained, corresponding to 87.62% and 96.45% respectively. Additionally, thermodynamic and kinetic calculations were carried out. It was concluded that the reaction was dominated by kinetics, with the distribution of three products being para > ortho > meta. The computational and experimental results indicated that the amination process involves an amino radical mechanism.

A Practical Homogeneous Nickel Catalyst for Reductive Amination of γ‐Keto Acids using Hydrogen

The reductive amination of levulinic and 2‐acetyl benzoic acids with hydrogen and various amines proceeds efficiently in the presence of a homogeneous Ni/triphos‐catalyst. The reaction rate of the overall process is significantly enhanced using 3,3,3‐trifluoroethanol (TFE) as solvent. The optimized synthetic protocol allows for a straightforward access of >20 examples of N‐functionalized pyrrolidinones in high yields (75% and >99%). Upscaling to 10 mmol‐scale is demonstrated and mechanistic in situ studies revealed the presence of alkoxy‐ and hydroxylactams as crucial intermediates.

Air-Stable Arene Manganese Complexes as Catalysts for the Syngas-Assisted Direct Reductive Amination, Cyanation of Aldehyde, and CO2 Fixation by Epoxide with High Functional Groups Tolerance.

Manganese complexes [(arene)Mn(CO)3]+ were prepared in one step from arenes and Mn(CO)5Br. They were found to be efficient catalysts in the carbonyl cyanation with TMSCN, CO2 fixation by epoxides, and direct reductive amination in the presence of syngas. The amination reaction tolerated various reducible functional groups. The synergy of carbon monoxide and hydrogen in syngas provides high efficiency of the catalytic system. The developed protocols do not require an inert atmosphere, and the catalysts can be handled in air.

Reaction Pathway Analysis of PET Deconstruction via Methanolysis and Tertiary Amine Catalysts.

Polyethylene terephthalate (PET) is a type of polymer frequently used in plastic packaging that significantly adds the amount of plastic waste found in landfills. One of the ways to recover valuable raw materials from postconsumer plastic is by depolymerizing PET into its monomeric constituents, which are dimethyl terephthalate (DMT) and ethylene glycol. PET depolymerization is often done in methanolysis with the help of acidic or base catalysts. Tertiary amine is one of the most attractive base catalysts for PET depolymerization in methanolysis since it does not lead to the generation of potentially environmentally harmful waste, unlike metal-based catalysts. However, the mechanism by which tertiary amines catalyze PET depolymerization in methanolysis remains unexplored. Developing a detailed mechanistic understanding of this process is important for improving plastic upcycling since it opens the possibility of employing various cheaper and more environmentally friendly reaction conditions. Using density functional theory and transition state analysis, we show that in the presence of tertiary amine catalysts, methanolysis of PET consists of multiple discrete-step reactions rather than a single concerted step. Furthermore, by comparing our calculations to recent experimental results, we were able to rationalize the DMT yield from the depolymerization process by relating it to charge polarization within tertiary amine catalysts, thus opening a pathway to identify atomic descriptors for future catalyst design.

Alkaline Modified Mesoporous Silica Supported Ruthenium Catalyst for Improved α-Amino Acid Synthesis.

Amino acids are a class of compounds with wide-ranging applications. The synthesis of amino acids from biomass-derived α-keto acids and ammonia is a sustainable way but the unstable primary imine intermediates (R-C=NH) easily form oligomers. Herein, targeting this problem, alkaline modified mesoporous silica was employed as a support for ruthenium (Ru/M-MCM-41), which could be used as a bifunctional catalyst in the reductive amination of α-keto acids to synthesize α-amino acids. The incorporation of Sr improved the dispersion of Ru nanoparticles and enhanced metal-support interactions via electron transfer from Sr to Ru, and the active Ru sites could efficiently hydrogenate primary imine intermediates to α-amino acids, thus prohibiting the formation of oligomers. Moreover, the Sr-dopant introduces base sites that could catalyze the hydrolysis of oligomers back to primary imine intermediates and finally hydrogenated to α-amino acids. As a result, >99% yield of glycine was achieved from glyoxylic acid over Ru/Sr-MCM-41, which is nearly three times that achieved over Ru/MCM-41 (32.2%).

Effective amine solvent regeneration over NiO-modified SBA-15 catalysts for energy-saving CO2 capture

Catalytic amine regeneration can decrease the energy required for regeneration; therefore, high economic and energy efficiency can be expected for CO2 capture. These factors necessitate the development of an inexpensive and easily synthesizable catalyst that can exhibit a high desorption efficiency. When selecting a catalyst, its physicochemical properties must be considered, because they markedly affect the chemical reaction between CO2–amine–catalyst. In this study, mesoporous silica SBA-15, particularly, rod-type SBA-15, wrinkled SBA-15 (modified from rod-type SBA-15), and NiO-impregnated rod-type and wrinkled SBA-15 catalysts were investigated in terms of the CO2 desorption rate and heat duty in a CO2–rich 5 M monoethanolamine (MEA) solution at 86 ℃. The physicochemical properties of the catalysts were compared to investigate their effect on the CO2 desorption efficiency. The performance of wrinkled SBA-15 impregnated with 10 wt% NiO in a CO2–rich MEA solution was optimal, exhibiting a 12 % higher CO2 desorption rate and 19.9 % lower heat duty than the MEA solution without a catalyst. Furthermore, the stability and reproducibility of the catalysts were confirmed through repeated experiments under identical conditions. Based on the experimental results and analysis, a plausible desorption mechanism for CO2–MEA–catalyst was proposed. It is expected that the regeneration heat duty during the CO2 regeneration can be effectively reduced by a catalyst, eventually applied to the CO2 capture.

Polysulfides for presulfiding of hydrogenation catalysts: synthesis, mechanism and applications

Presulfiding agents are widely used in oil refining and chemical industry, how to produce safe and efficient presulfiding agent by more environmentally friendly synthesis process are still problems to be solved. In this study, the organic polysulfide FSA-55 was synthesized by a practical one-pot process using isobutene and sulfur as raw materials and organic amine as a catalysts. The product components were analyzed and the possible catalytic reaction pathways in the thermal conversion of sulfides were elucidated. The amine catalysts showed a catalytic activities in inducing the ring opening of the cyclic molecular structure of sulfur at high temperature, thereby releasing the reactive sulfur radicals, which react with unsaturated double bonds through addition reactions. Different molecular structures of polysulfide were generated through molecular rearrangement and cyclization reactions. The suitability of the product as a presulfiding agent was investigated by analyzing the thermal properties and studying the presulfiding effect on hydrogenation catalysts. The polysulfide has a wide decomposition temperature range (100–260 °C), which can effectively avoid the occurrence of concentrated exothermic phenomena during presulfiding of hydrogenation catalysts. The presulfiding degree of the catalysts can reach 58.32%, which shows the great potential of oil processing as a presulfiding agent.

Nonsilyl Bicyclic Secondary Amine Catalysts for the Asymmetric Transfer Hydrogenation of α,β-Unsaturated Aldehydes.

The first chiral synthesis of nonsilyl bicyclic secondary amine organocatalysts and their application to the asymmetric transfer hydrogenation of α,β-unsaturated aldehydes are disclosed. A lower catalytic loading (5 mol %) is demonstrated for the reduction of a wide range of α,β-unsaturated aldehydes (up to 97% yield and up to 99% ee). The application of this scalable methodology is showcased for the asymmetric synthesis of bioactive molecules such as phenoxanol, citronellol, ramelteon, and terikalant.

Fluorinated Chiral Pyrans Obtained via Mechanochemical Organocatalytic Michael/oxa‐Michael Cascade

Fluorine‐containing compounds are important in medicine or crop‐protection. Herein, we show asymmetric organocatalytic Michael/oxa‐Michael cascade leading to chiral fluorinated pyrans under mechanochemical conditions. Formal oxa‐Diels‐Alder reaction between fluorine containing unsaturated keto esters and β,γ‐unsaturated ketones afforded a range of drug‐like pyran derivatives in short times and good to high yields. Ball‐milling convey the reaction in short times and high product yields, while keeping high enantiomeric purities of products. The reaction is diastereodivergent depending on the use of either monofunctional amine catalysts or bifunctional thiourea or squaramide.

SELECTION OF SUITABLE CATALYSTS FOR PRODUCTION OF NEW NANOCOMPOSITE MATERIALS

The article is devoted to the principles of hydrolytic polycondensation of tetramethoxysilane (TMOS) in an alkaline environment. Monolithic samples of SiO2 particles and xerogels were synthesized as a result of hydrolytic polycondensation of tetramethoxysilane in alkaline medium. Amine catalysts - pyridine derivatives were used to carry out the process. As a result, samples of different sizes were synthesized depending on the concentration of substances taken as catalysts. Smaller diameter particles were obtained at lower amine concentrations and larger diameter particles at higher concentrations. As the pKa value of the catalysts used in the synthesis of xerogels increases, certain increases and decreases in the properties of the resulting particles have been observed. Thus, with an increase in the pKa value, the density and hardness of the samples decreased, the percentage of SiO2 increased, and at the same time, the gelation time in the sol-gel system decreased. Images of the synthesized particles were obtained using a scanning electron microscope (SEM). Keywords: sol-gel, hydrolysis, polycondensation, tetramethoxysilane, xerogel, pKa, catalyst, SEM.

Enantioselective Synthesis of α-Quaternary Isochromanes by Oxidative Aminocatalysis and Gold Catalysis.

A novel strategy that combines oxidative aminocatalysis and gold catalysis allows the preparation of chiral α-quaternary isochromanes, a motif that is prevalent in natural products and synthetic bioactive compounds. In the first step, α-branched aldehydes and propargylic alcohols are transformed into α-quaternary ethers with excellent optical purities (>90 % ee) via oxidative umpolung with DDQ and an amino acid-derived primary amine catalyst. Subsequent gold(I)-catalyzed intramolecular hydroarylation affords the isochromane products with retention of the quaternary stereocenter. A second approach explores the use of allylic alcohols as reaction partners for the oxidative coupling to furnish α-quaternary ethers with generally lower enantiopurities. Stereoretentive cyclization to isochromane products is achieved via intramolecular Friedel-Crafts type alkylation with allylic acetates as a reactive handle. A number of synthetic elaborations and a biological study on these α-quaternary isochromanes highlight the potential applicability of the presented method.

Enantioselective Transformations by "1 + x" Synergistic Catalysis with Chiral Primary Amines.

ConspectusSynergistic catalysis is a powerful tool that involves two or more distinctive catalytic systems to activate reaction partners simultaneously, thereby expanding the reactivity space of individual catalysis. As an established catalytic strategy, organocatalysis has found numerous applications in enantioselective transformations under rather mild conditions. Recently, the introduction of other catalytic systems has significantly expanded the reaction space of typical organocatalysis. In this regard, aminocatalysis is a prototypical example of synergistic catalysis. The combination of aminocatalyst and transition metal could be traced back to the early days of organocatalysis and has now been well explored as an enabling catalytic strategy. Particularly, the acid-base properties of aminocatalysis can be significantly expanded to include usually electrophiles generated in situ via metal-catalyzed cycles. Later on, aminocatalyst has also been exploited in synergistically combining with photochemical and electrochemical processes to facilitate redox transformations. However, synergistically combining one type of aminocatalyst with many different catalytic systems remains a great challenge. One of the most daunting challenges is the compatibility of aminocatalysts in coexistence with other catalytic species. As nucleophilic species, aminocatalysts may also bind with metal, which leads to mutual inhibition or even quenching of the individual catalytic activity. In addition, oxidative stability of aminocatalyst is also a non-neglectable issue, which causes difficulties in exploring oxidative enamine transformations.In 2007, we developed a vicinal diamine type of chiral primary aminocatalysts. This class of primary aminocatalysts was developed and evolved as functional and mechanistic mimics to the natural aldolase and has been widely applied in a number of enamine/iminium ion-based transformations. By following a "1 + x" synergistic strategy, the chiral primary amine catalysts were found to work synergistically or cooperatively with a number of transition metal catalysts, such as Pd, Rh, Ag, Co, and Cu, or other organocatalysts, such as B(C6F5)3, ketone, selenium, and iodide. Photocatalysis and electrochemical processes can also be incorporated to work together with the chiral primary amine catalysts. The 1 + x catalytic strategy enabled us to execute unexploited transformations by fine-tuning the acid-base and redox properties of the enamine intermediates and to achieve effective reaction and stereocontrol beyond the reach individually. During these efforts, an unprecedented excited-state chemistry of enamine was uncovered to make possible an effective deracemization process. In this Account, we describe our recent efforts since 2015 in exploring synergistic chiral primary amine catalysis, and the content is categorized according to the type of synergistic partner such that in each section the developed synergistic catalysis, reaction scopes, and mechanistic features are presented and discussed.

Molybdenum-doped carbon nitride as an efficient heterogeneous catalyst for direct amination of nitroarenes with arylboronic acids

Heterogeneous metal-catalyzed chemical conversions with a recyclable catalyst are very ideal and challenging for sustainable organic synthesis. A new bipyridyl-Mo(IV)-carbon nitride (CN-K/Mo-Bpy) was prepared by supporting molybdenum complex on C3N4-K and characterized by FT-IR, XRD, SEM, XPS and ICP-OES. Heterogeneous CN–Mo-Bpy catalyst can be applied to the direct amination of nitroarenes and arylboronic acid, thus constructing various valuable diarylamines in high to excellent yields with a wide substrate scope and good functional group tolerance. It is worth noting that this heterogeneous catalyst has high chemical stability and can be recycled for at least five times without reducing its activity.

Innovative Application of Polyether Amine as a Recyclable Catalyst in Aerobic Thiophenol Oxidation

Polyether amines are versatile compounds characterized by a flexible structure, consisting of polyoxypropylene and polyoxyethylene as the backbone, with amine groups at each end. They have widespread applications in various industrial processes and daily life. Despite their versatility, the utilization of polyether amines as base catalysts is rare. In this study, one kind of three-arm polyether amine 1 was employed as an environmentally friendly, cost-effective catalyst for the aerobic oxidation of thiophenols, leading to the synthesis of disulfides. The oxidative coupling of thiols serves as a fundamental pathway for the production of disulfides, which are vital in both chemical and biological processes. In contrast to known methods for thiol oxidation, this polyether amine-based catalytic process eliminates the need for expensive stoichiometric oxidants and minimizes the formation of over-oxidized by-products. Using a mere 0.5 mol % of the polyether amine 1 as the catalyst, a remarkable > 96% yield was achieved for all 16 tested substrates, encompassing a diverse range of functional groups, under the catalytic aerobic oxidation conditions. Furthermore, it is noteworthy that over 90% of the polyether amine catalyst can be efficiently recovered for reuse without loss of activity, making this a sustainable and cost-effective catalytic approach.