Activity For Knoevenagel Condensation Research Articles

Exploring surface silanols in mesoporous Na-LTA zeolite to enhance its catalytic activity in knoevenagel condensation by grafting amino groups

Mesoporous Na-LTA zeolite was synthesized using the surfactant templating method with the organosilane surfactant [3-(trimethoxysilyl)propyl] octadecyldimethylammonium chloride (TPOAC). The formation of mesopores not only improved the accessibility of the basic catalytic sites but also led to the formation of isolated external silanols. These silanols were used to anchor propylamine groups by reacting with 3-aminopropyltrimethoxysilane (APTMS). The incorporation of propylamine groups in the mesoporous Na-LTA improved its catalytic activity in the Knoevenagel condensation reaction by 40 % due to the presence of extra basic catalytic sites from amino groups. The combination of mesopore generation and functionalization is an efficient strategy for enhancing the performance of Na-LTA zeolite in this reaction.

Modified nano magnetic Fe2O3-MgO as a high active multifunctional heterogeneous catalyst for environmentally beneficial carbon–carbon synthesis

In this study, novel nanomagnetic catalysts, namely Fe2O3-MgO@choline formate (Ch. F.) and Fe2O3-MgO@choline cyanide (Ch. CN), were synthesized through immobilizing choline-based ion liquids to magnetic support via a simple and cost-effective methodology. FT-IR, TGA, FE-SEM, VSM, EDS, BET, and XRD techniques were employed to assess and characterize these organic–inorganic compounds. Following the successful preparation of nanoparticles, the catalysts were utilized in Knoevenagel and benzoin condensations. Fe2O3-MgO@Ch.F. exhibited exceptional activity in Knoevenagel condensation under solvent-free conditions at room temperature, achieving high yields (91–98%) in a short timeframe. Similarly, Fe2O3-MgO@Ch.CN demonstrated remarkable activity in benzoin condensation under environmentally friendly solvent conditions, yielding higher isolated yields (76–88%). Furthermore, these magnetically recyclable multifunctional catalysts displayed the ability to be reused up to five times without a significant loss in efficiency. Additionally, the heterogeneity of this nanocatalyst was investigated using the hot filtration technique. The findings indicated that the reaction primarily occurs via a heterogeneous pathway.

Tris(2-Aminoethyl)Amine/Metal Oxides Hybrid Materials-Preparation, Characterization and Catalytic Application.

Three different metal oxides (basic MgO, basic-acidic Al2O3 and acidic-basic Nb2O5) characterized by comparable surface areas (MgO—130 m2/g; Al2O3—172 m2/g and Nb2O5—123 m2/g) and pore systems (domination of mesopores with narrow pore size distribution) were modified with tris(2-aminoethyl)amine (TAEA) via two methods: (i) direct anchoring of amine on metal oxide and (ii) anchoring of amine on metal oxide functionalized with (3-chloropropyl)trimethoxysilane. The obtained hybrid materials were characterized in terms of effectiveness of modifier anchoring (elemental analysis), their structural/textural properties (nitrogen adsorption/desorption, XRD), acidity/basicity of support (2-propanol dehydration and dehydrogenation, dehydration and cyclization of 2,5-hexanedione), states of modifier deposited on supports (XPS, FTIR, UV–VIS) and the strength of interaction between the modifier and the support (TG/DTG). It was evidenced that acidic-basic properties of metal oxides as well as the procedure of modification with TAEA determined the ways of amine anchoring and the strength of its interaction with the support. The obtained hybrid materials were tested in Knoevenagel condensation between furfural and malononitrile. The catalysts based on MgO showed superior activity in this reaction. It was correlated with the way of TAEA anchoring on basic MgO and the strength of modifier anchoring on the support. To the best of our knowledge tris(2-aminoethyl)amine has not been used as a modifier of solid supports for enhancement of the catalyst activity in Knoevenagel condensation.

Calcium and nitrogen species loaded into SBA-15 - a promising catalyst tested in Knoevenagel condensation.

Mesoporous silica of the SBA-15 type was used as a support for basic active centers generated by the incorporation of calcium species and (3-aminopropylo)trimethoxysilane (APTMS) or imidazole. The samples were characterized by low temperature N2 adsorption/desorption, XRD, XPS, FTIR spectroscopy, CO2-TPD, and elemental and thermal analyses. Calcium containing samples were analysed in 2,5-hexanedione dehydration and cyclization, while the activities of all the samples were examined in Knoevenagel condensation between benzaldehyde and malononitrile. It was demonstrated that the calcium species interacted with a silica support increasing the stabilization of organosilanes on the SBA-15 surface. A very high activity of the catalysts in Knoevenagel condensation indicated a synergistic interaction between calcium and the organic modifiers.

Impact of Brønsted acid sites in MWW zeolites modified with cesium and amine species on Knoevenagel condensation

Abstract Layered zeolites of MWW family, MCM-22 and pillared MCM-36, were used as supports for base modifiers: cesium species (introduced via cation exchange or impregnation) and 3-aminopropyl trimethoxysilane (AP). The obtained materials were characterized by different methods (ICP-OES, N2 adsorption, XRD, XPS, TG/DTA, FTIR combined with pyridine adsorption, 2-propanol decomposition) for evaluation of chemical, structural and surface properties. All materials obtained were subjected to the Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate and ethyl acetoacetate. The effect of the zeolite structure, the stability of the catalysts as well as acid-base properties of zeolites on the activity in Knoevenagel condensation were considered. Of particular interest was the role of Bronsted acid sites (BAS). The nature of basic sites and BAS played different roles depending on the methylene compound used in the Knoevenagel condensation. AP-modified zeolites were the most active in the condensation between benzaldehyde and ethyl cyanoacetate, in which, in the first step of the reaction AP abstracted hydrogen from methylene carbon in ethyl cyanoacetate. A different reaction pathway was postulated for the condensation with ethyl acetoacetate on the basis of the highest activity of unmodified zeolites and the relationship between benzaldehyde conversion and the number of BAS. For this reaction protonation of benzaldehyde was postulated as the initial step of the reaction.

Heterogeneous Organocatalysts Based on a Triazine‐Triazole Silane Ligand

Robust and non‐air‐sensitive metal‐free triazine‐triazole heterogeneous organocatalysts were prepared. The synthetic procedure involved the co‐condensation of a bridged tris silane precursor with tetraethyl orthosilicate (TEOS) in the presence of cetyltrimethylammonium bromide (CTAB). In addition, the silane precursor was anchored post‐synthesis onto mesoporous silica nanoparticles and used to stabilize magnetic nanoparticles. The organocatalysts were characterized by X‐ray diffraction (XRD), X‐ray fluorescence (XRF), N2 adsorption‐desorption, transmission electron microscopy (TEM), solid‐state nuclear magnetic resonance spectroscopy (CP‐MAS‐NMR), Fourier‐transform infrared spectroscopy (FT‐IR), and UV/Vis diffuse reflectance spectroscopy (DRUV/Vis). All materials, recoverable and recyclable, possess good catalytic activity in Knoevenagel condensation and in the one‐pot three‐component reaction for the synthesis of 2‐amino‐chromene derivatives under mild conditions.

Regulation of polar microenvironment on the surface of tertiary amines functionalized polyacrylonitrile fiber and its effect on catalytic activity in Knoevenagel condensation

Two fiber supported tertiary amine catalysts were prepared by immobilization of 3-dimethylamino-1-propylamine (PANDF) and 3-dimethylamino-N-methylpropylamine (PANTF) on polyacrylonitrile fiber. Both fiber catalysts contain polar microenvironments constructed by amide groups, tertiary amine groups and unreacted cyano groups. The difference between the two catalysts lies in that the PANDF contains hydrogen bond network while the PANTF does not. Employing Knoevenagel condensation as a model reaction, the cooperative action of immobilized tertiary amines with hydrogen bonds was evaluated in detail. At the same time, the aggregation of reactants in the polar microenvironment under different solvents was also investigated. The results showed that hydrogen bonds and the supporting basic groups can promote the reaction by the synergistic catalytic effect in most solvents. The catalysts displayed different catalytic behaviors in solvents with different polarities. The catalysts can achieve highly efficient catalytic activity in the more polar solvents which were well compatible with the catalysts. Moreover, the reaction can also occur in less polar solvents due to their incompatible property with the fiber catalysts, which can compel the polar reactants to accumulate on the fiber surface with strong polar microenvironment.

2-Methylimidazole-assisted synthesis of a two-dimensional MOF-5 catalyst with enhanced catalytic activity for the Knoevenagel condensation reaction

A novel and facile strategy was developed for the synthesis of a 2D MOF-5 catalyst with 2-methyimidazole as regulation reagent and a Lewis basic site, which showed excellent catalytic activity in Knoevenagel condensation.

Synthesis and characterization of sulfamic acid supported on Fe3O4 nanoparticles: A green, versatile and magnetically separable acidic catalyst for oxidation reactions and Knoevenagel condensation

Sulfamic acid immobilized on diethylenetriamine functionalized Fe3O4 nanoparticles (SA‐DETA‐Fe3O4) was successfully prepared and characterized by X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FT‐IR), vibrating sample magnetometer (VSM), thermo gravimetric analysis (TGA), X‐Ray diffraction (XRD) and scanning electron microscopy (SEM). The sulfamic acid was found as a magnetically separable and highly active catalyst for the oxidative coupling thiols, oxidation of sulfides. Furthermore, the SA‐DETA‐Fe3O4 showed the high catalytic activity in Knoevenagel condensation of aromatic aldehydes with active methylene compounds (malononitrile and ethyl cynoacetate). The nanosolid catalyst could be easily recovered by a simple magnetic separation and reused for many cycles without deterioration in catalytic activity.

Synthesis, characterization and heterogeneous base catalysis of amino functionalized lanthanide metal-organic frameworks

Lanthanide metal-organic frameworks (Ln-MOFs) are featured by their tolerance to water and dense structure. In this work, an amine-functionalized Ln-MOF was facilely synthesized by coordination of terbium with 2-aminoterephthalic acid under the condition of microwave irradiation. The crystal structure was characterized by single crystal X-ray diffraction, FT-IR, Raman, TG-DTA and XPS analysis. The basic catalytic activity of the NH2-Tb-MOF was evaluated for Knoevenagel condensation and Henry reactions. Apart from the high activity and 100% selectivity to the condensation product, the NH2-Tb-MOF catalyst could be easily recycled and reused owing to the high stability of the MOF framework formed by coordination of Tb3+ with carboxylic groups. Remarkably, the NH2-Tb-MOF exhibited size-selective catalysis to substrates. For the small-sized reactants, it displayed comparable activity to the homogeneous catalyst of aniline owing to the high dispersion of NH2− active sites and the low diffusion limits. However, in the same reaction system, extremely poor activity in Knoevenagel condensation and Henry reaction for the bulky substrate 4-(tert-butyl) benzaldehyde was observed due to the both effects of substitute and inhibition of diffusion into the micropores. Crystal structure analysis provided a mechanistic evidence that the heterogeneous base catalysis arose from the amino groups densely distributed inside the micropores.

Synthesis of KOH/SnO2 solid superbases for catalytic Knoevenagel condensation

KOH/SnO2 solid superbases of specific morphology and uniform pore structure were synthesized. The SnO2 support was prepared by reflux digestion using graphene oxide as template and employed for the loading of KOH by means of grinding and thermal treatment. With base strength of 26.5≤H−<33.0 and superbasic sites of 1.362mmolg−1, the 20wt.%KOH/SnO2 catalyst exhibits excellent activity in Knoevenagel condensation under mild conditions. The catalytic efficiency is closely related to the base strength and the amount of superbasic sites. The findings disclose a new route for the synthesis of versatile solid superbases using SnO2 as supports.

Ce(III) and Lu(III) metal–organic frameworks with Lewis acid metal sites: Preparation, sorption properties and catalytic activity in Knoevenagel condensation

Two novel coordination polymers with composition {[Ln(BTC)(H2O)]·DMF}n (where Ln=Ce(III) (1) and Lu(III) (2), BTC=benzene-1,3,5-tricarboxylate, DMF=N,N′-dimethylformamide) have been prepared under solvothermal conditions. Properties of the compounds were investigated by single crystal X-ray diffraction, high-energy powder X-ray diffraction during in-situ heating, thermogravimetry with simultaneous evolved gas analysis, infrared spectroscopy performed at different temperatures, elemental analysis and inductively coupled plasma mass spectrometry. Sorption properties of the synthesized complexes were investigated using nitrogen and carbon dioxide adsorption experiments. Catalytic activity of compound 2 was tested in Knoevenagel condensation reactions in a series of aromatic and non-aromatic aldehydes with different active methylene compounds (malononitrile, methyl cyanoacetate), in which the reactivity of aldehydes in condensation reactions increases in the order: 2-naphthaldehyde<4-tert-butyl benzaldehyde<benzaldehyde<cyclohexane carbaldehyde<n-heptanal.

Polyvinyl amine coated Fe3O4@SiO2 magnetic microspheres for Knoevenagel condensation

Polyvinyl amine coated Fe 3 O 4 @SiO 2 composite microspheres with a core-shell structure were prepared and employed as a magnetic catalyst for Knoevenagel condensation under mild conditions. The catalyst can be readily recovered using a magnet and reused several times without loss in activity or selectivity. The performance of the magnetic base catalyst was compared with that of polyvinyl amine functionalized mesoporous SBA-15, which showed that the magnetic nanoparticles gave improved reaction rate and yield. Polyvinyl amine coated Fe 3 O 4 @SiO 2 was prepared by a simple method. This new magnetic catalyst exhibited high catalytic activity in Knoevenagel condensation of various aromatic and aliphatic aldehydes under mild conditions along with excellent level of reusability.

A novel nickel metal–organic framework with fluorite-like structure: gas adsorption properties and catalytic activity in Knoevenagel condensation

A new non-interpenetrating 3D metal-organic framework {[Ni4(μ6-MTB)2(μ2-H2O)4(H2O)4]·10DMF·11H2O}n (DMF = N,N'-dimethylformamide) built from nickel(ii) ions as connectors and methanetetrabenzoate ligands (MTB(4-)) as linkers has been synthesized and characterized. The single crystal X-ray diffraction showed that complex exhibits CaF2-like fluorite structure topology and four types of 3D channels with sizes about 12.6 × 9.4 Å(2), 9.4 × 8.0 Å(2), 12.6 × 11.7 Å(2) and 14.9 × 14.9 Å(2), which are filled with guest molecules. Conditions of the activation of the compound have been studied and optimized by powder X-ray diffraction during in situ heating, thermogravimetric analysis and infrared spectroscopy. Nitrogen and carbon dioxide adsorption showed that the activated sample exhibits a BET specific surface area of 700 m(2) g(-1) and a carbon dioxide uptake of 12.36 wt% at 0 °C, which are the highest values reported for the compounds of the MTB(4-) series. The complex was tested in Knoevenagel condensation of aldehydes and active methylene compounds. Straightforward dependence of the substrate conversion on the size of used aldehyde was established. A possible mechanism of Knoevenagel condensation over a MTB(4-) containing a metal-organic framework was proposed.

Novel Basic Ionic Liquid Based on Alkylammonium as Efficient Catalyst for Knoevenagel Reaction

The typical Knoevenagel condensation was carried out smoothly in the presence of a basic ionic liquid of N,N,N′,N′-tetramethyl-N′-hexyl-ethylenediammonium tetrafluoroborate ([TMHEDA]BF4), and 99% of yield was obtained using ethyl cyanoacetate and benzaldehyde as substrates at 60 °C for 1 h. Four reuses of the ionic liquid without dramatic decrease in catalytic activity for Knoevenagel condensation demonstrated the good stability and operability of the ionic liquid. Moreover, the typical nucleophilic addition reactions were also accomplished by the same ionic liquid to check its feasibility. The dual function of the basic ionic liquid both as solvent and catalyst, combined with simple product separation and recycling, is expected to contribute to the development of a green and environmentally friendly strategy.

Influence of basic properties of Mg,Al-mixed oxides on their catalytic activity in knoevenagel condensation between benzaldehyde and phenylsulfonylacetonitrile

The catalytic performance of Mg,Al-mixed oxides (MO20, MO25 and MO33) derived from hydrotalcites was evaluated in the Knoevenagel reaction between benzaldehyde and phenylsulfonylacetonitrile at 373 and 383 K. The best results were obtained for the sample MO20 that presented the highest basic sites density and external area and the smallest crystallite sizes. The relative amount of basic sites with weak to intermediate strength also played an important role on catalytic performance. By increasing the catalyst content from 1 to 5 wt.% at 383 K, a complete conversion of the reactants is attained, producing α-phenylsulfonylcinnamonitrile with a selectivity of 100%.

Basic Ionic Liquid: A Reusable Catalyst for Knoevenagel Condensation in Aqueous Media

An efficient, environmentally friendly procedure was developed for the condensation of aldehydes/ketones and activated methylene compounds with basic ionic liquid as the catalyst in water. This basic ionic liquid catalyst has a very high activity for Knoevenagel condensation to give the corresponding products in 70%–97% isolated yields under mild conditions. The basic ionic liquid catalyst in aqueous system can be reused for six times without any significant loss of activity.

Nitrogen-Incorporated SAPO-11 Molecular Sieve: Synthesis, Characterization, and Properties

Nitrogen-incorporated SAPO-11 molecular sieves were synthesized by a secondary synthesis technique at low nitridation temperature (400 °C) with a starting material of SAPO-11 zeolite doped with 2 wt % Ru. The obtained powder samples showed high activity in Knoevenagel condensation, which acts as a probing reaction for base catalysis. The changes in structure of the nitrogen-incorporated samples were investigated by means of 27Al-MAS NMR and 31P-MAS NMR spectra, X-ray diffraction, and BET surface area measurements. It was found that nitrogen-containing species had incorporated into the framework of SAPO-11 zeolite, in which some N atoms directly bonded to Al and P atoms and formed AlN4, AlN2O2, and PN4 groups. These species with terminal −NH2 groups on the surface together were responsible for the basicity of nitrogen-incorporated SAPO-11 zeolite.

New basic mesoporous silica catalyst obtained by ammonia grafting.

NH3-treated mesoporous silica (FSM-16) contains SiNH2 sites which exhibit basic catalytic activity for Knoevenagel condensation; SiNH2 and SiOH pair sites formed at lower NH3-treatment temperatures exhibit higher turnover frequencies (TFs) in comparison with SiNH2 single sites.