Heterogeneous Catalyst For Knoevenagel Condensation Research Articles

Magnetite nanoparticles immobilized on hydrophilic polyelectrolyte-grafted carbon nanotube as efficient organic–inorganic hybrid heterogeneous catalyst for Knoevenagel condensation in aqueous medium

In this work, a novel organic–inorganic hybrid heterogeneous catalyst was fabricated for Knoevenagel condensation. First, the surface of carbon nanotube (CNT) was covalently functionalized with poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) polyelectrolyte (i.e., organic polybase) through the surface-initiated atom transfer radical polymerization (SI-ATRP) method. Subsequently, magnetic iron oxide nanoparticles (Fe3O4 NPs) (i.e., inorganic Lewis acid) are densely and homogeneously grown on the CNT surface using the CNT-g-PDMAEMA template. The as-prepared acid–base bifunctional catalyst (i.e., CNT-g-PDMAEMA/Fe3O4NPs) was investigated in the model reaction, i.e., Knoevenagel condensation between naphthol, malononitrile and benzaldehyde. The CNT-g-PDMAEMA/Fe3O4NPs catalyst shows high catalytic activity in the Knoevenagel condensation between naphthol, malononitrile and benzaldehyde due to its unique structure and specific chemical constitution. In addition, this acid–base bifunctional catalyst can be readily recovered with an applied magnetic field and reused with negligible loss in the catalytic activity even after six cycles.

Metal–organic frameworks constructed using acid–base mixed ligands, carboxylic acids and N-containing chalcone, and their catalytic performance for Knoevenagel condensation

MOF materials constructed using acid–base mixed ligands serve as efficient and economical porous heterogeneous catalysts for Knoevenagel condensation.

COF-supported zirconium oxyhydroxide as a versatile heterogeneous catalyst for Knoevenagel condensation and nerve agent hydrolysis

A composite of catalytic Lewis acidic zirconium oxyhydroxides (8 wt%) and a covalent organic framework (COF) was synthesized. X-ray diffraction and infrared (IR) spectroscopy reveal that COF's structure is preserved after loading with zirconium oxyhydroxides. Electron microscopy confirms a homogeneous distribution of nano- to sub-micron-sized zirconium clusters in the COF. 3D X-ray tomography captures the micron-sized channels connecting the well-dispersed zirconium clusters on the COF. The crystalline ZrOx(OH)y@COF's nanostructure was model-optimized via simulated annealing methods. Using 0.8 mol% of the catalyst yielded a turnover number of 100-120 and a turnover frequency of 160-360 h-1 for Knoevenagel condensation in aqueous medium. Additionally, 2.2 mol% of catalyst catalyzes the hydrolysis of dimethyl nitrophenyl phosphate, a simulant of nerve agent Soman, with a conversion rate of 37% in 180min. The hydrolytic detoxification of the live agent Soman is also achieved. Our study unveils COF-stabilized ZrOx(OH)y as a new class of zirconium-based Lewis+ Bronsted-acid catalysts.

Ru-bentonite catalyzed green Knoevenagel condensation of substituted benzaldehydes with ethyl cyanoacetate

The full-text of the article will be published in the English version of the journal "Catalysis in Industry" No. 1, 2024.To develop Ru-incorporated bentonite clay as a heterogeneous base catalyst for use in Knoevenagel condensation as an alternative to hazardous base catalysts like pyridine, piperidine, etc., we purify the naturally occurring bentonite clay and Ru3+ cation incorporated into its interlayers of bentonite clay to improve its porosity and to increase the surface area of bentonite clay. Purified bentonite and Ru-bentonite were characterized by FTIR, PXRD, HRTEM, SEM & EDS, BET surface area analysis, and TGA. Base activation was done to these clays and a comparative study of these clays as recyclable heterogeneous catalysts for Knoevenagel Condensation was undertaken in water as a solvent for the chemical transformation of 2,4-dichlorobenzaldehyde and 4-hydroxybenzaldehyde with ethyl cyanoacetate into their corresponding α,β-unsaturated acids. The products were characterized by FTIR, 1H NMR, and 13C NMR analyses. The essential key points of this reaction are mild reaction conditions, absence of hazardous chemicals as used in classical Knoevenagel condensation, reusability of the catalyst, and high yield percentage of the products.

Amine-rich Nickel(II)-Xerogel as a Highly Active Bifunctional Metallo-organo Catalyst for Aqueous Knoevenagel Condensation and Solvent-free CO2 Cycloaddition.

Metallogels formed from supramolecular interactions of low-molecular-weight gelators (LMWGs) combine the qualities of heterogeneous catalysts and offer the advantages of multifunctionality owing to the facile installation of desired task-specific moieties on the surface and along the channels of the gels. We discuss the applications of a triazole-based Ni(II) gel-derived xerogel (NiXero) having a high density of Ni(II)-nodes and appended primary amines as a recyclable heterogeneous catalyst for Knoevenagel condensation of aldehyde and malononitrile in water and the solvent-free cycloaddition of CO2 to form a series of cyclic carbonates with near-quantitative conversion of the respective epoxides, with low catalyst loading (0.59 mol %), high catalyst stability, and recyclability. The structural advantages of NiXero, due to the concurrent presence of bifunctional Lewis acid-base sites on the channels, open Ni(II) nodes, Ntriazole, pendant -NH2 and its chemical stability, are conducive to the cooperative heterogeneous catalytic activity under mild conditions. This work emphasizes the effective amalgamation of metals with purpose-built ligand systems for the construction of metallogels and their utility as heterogeneous catalysts for desired organic transformations.

Nitrogen-Enriched Biguanidine-Functionalized Cobalt Ferrite Nanoparticles as a Heterogeneous Base Catalyst for Knoevenagel Condensation under Solvent-Free Conditions.

Designing efficient, economical heterogeneous catalysts for the Knoevenagel condensation reaction is highly significant owing to the importance of reaction products in industries as well as pharmaceutics. Herein, we have designed and synthesized biguanidine-functionalized basic magnetically retrievable cobalt ferrite nanoparticles (CFNPs) for the synthesis of Knoevenagel condensation products using benzaldehydes and active methylene compounds (malononitrile/ethyl cyanoacetate/cyanoacetamide). Several advanced techniques, such as Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and vibration sample magnetometry (VSM), were utilized to precisely characterize the catalyst. The robust features of the current approach involve outstanding catalytic performance, solvent-free reaction conditions, ease of catalyst retrievability, easy workup procedure, large substrate tolerance, high turnover frequency (TOF) values (up to 486.88 h-1), values of green chemistry metrics such as E-factor (0.15), reaction mass efficiency (RME) value (87.07%), carbon efficiency (93.4%), and atom economy (AE) value (88.10%) close to their ideal values, and recyclability up to eight runs without a considerable reduction in activity, boosting the appeal of this approach from a commercial and ecological point of view.

A layered metal‐organic framework with acidic sites as a multiphase catalyst for Knoevenagel condensation

AbstractA layered metal‐organic framework Zn‐TPN was designed and fabricated by solvothermal reaction. The crystal structure was a lamellar structure, and the unique coordination pattern provided Lewis acid sites that could be employed as efficient catalytic sites. Zn‐TPN displayed a satisfactory catalytic effect for Knoevenagel condensation of malononitrile and benzaldehyde. At 75 °C, the conversion rate reached 96.96 % basing on the acidic sites after 1 hour, and it showed ideal catalytic activities for Knoevenagel condensation containing various aldehydes. Zn‐TPN could be utilized as a promising heterogeneous catalyst for Knoevenagel condensation.

Metal–organic frameworks with open metal sites act as efficient heterogeneous catalysts for Knoevenagel condensation and the Chan–Lam coupling reaction

Two robust metal–organic Frameworks (MOFs) with distinct and diverse network topologies containing open metal sites are successfully employed as heterogeneous catalysts for the Knoevenagel condensation and the Chan–Lam cross coupling reaction.

Efficient and green one‐pot synthesis of Knoevenagel condensation catalyzed nano metal–organic frameworks in water

Metal–organic frameworks (MOFs), Mlam‐NH‐66‐UiO and EtA‐NH‐66‐UiO, were prepared via post‐synthesis of the H2N‐66‐UiO and used as an efficient heterogeneous catalyst for Knoevenagel condensation of various aldehydes with malononitrile in water. The modified MOFs exhibited excellent catalyst activities in heterogeneous phase because of their large pore sizes and surface area, porosity, and the number of catalytically active sites (–NH2) on structures. In addition, the catalysts can be recycled and reused without decomposition of MOF structure and losing catalytic activity.

A Stable Y(III)-Based Amide-Functionalized Metal-Organic Framework for Propane/Methane Separation and Knoevenagel Condensation.

Here, a Y(III)-based metal-organic framework, JLU-MOF112 {[Y3(μ3-O)2(μ3-OH)(H2O)2(BTCTBA)2]·2[(CH3)2NH2]·5DMF·C6H5Cl·4H2O}, has been successfully synthesized under solvothermal conditions. JLU-MOF112 was constructed with amide-functionalized tricarboxylate ligands and Y(III)-based infinite chains, where the Y3 repeating units are arranged in a trans order. The overall framework could be viewed as a novel (3,5)-connected net with two types of channels along the [100] and [010] directions. JLU-MOF112 possesses a large BET surface area (1553 m2 g-1), a permanent pore volume (0.67 cm3 g-1), and outstanding thermal and chemical stability, which give JLU-MOF112 potential for the purification of natural gas, especially the equimolar separation of C3H8/CH4 with a high selectivity of 176. In addition, benefiting from the amide functional groups as Brønsted basic sites and the exposure of open metal sites as Lewis acid sites after activation, JLU-MOF112 can serve as a high-efficiency heterogeneous catalyst for Knoevenagel condensation by the reactions of malononitrile with benzaldehyde (yield of 98%, turnover number of 392, and turnover frequency of 3.27 min-1) and diverse aldehyde compounds. A rational mechanism was put forward that the Knoevenagel condensation was catalyzed by the synergistic effect of the Lewis acid sites and Brønsted basic sites, engendering the polarization of the carbonyl groups and the deprotonation of the methylene groups for nucleophilic attack.

Pyrrole-Based Conjugated Microporous Polymers as Efficient Heterogeneous Catalysts for Knoevenagel Condensation.

Conjugated microporous polymers (CMPs) with robust architectures, facilely tunable pore sizes and large specific surface areas have emerged as an important class of porous materials due to their demonstrated prospects in various fields, e.g. gas storage/separation and heterogeneous catalysis. Herein, two new pyrrole-based CMPs with large specific surface areas and good stabilities were successfully prepared by one-step oxidative self-polycondensation of 1,2,4,5-tetra (pyrrol-2-ly)benzene or 1,3,5-tri (pyrrol-2-ly)benzene, respectively. Interestingly, both CMPs showed very high catalytic activity toward Knoevenagel condensation reaction, which was attributed to the inherent pore channels, high specific surface areas and abundant nitrogen sites within CMPs. Additionally, both CMPs displayed excellent recyclability with negligible degradation after 10 cycles. This work provides new possibilities into designing novel nitrogen-rich high-performance heterogeneous catalysts.

Bis [hydrazinium (1+)] hexafluoridosilicate:(N2H5)2SiF6 novel hybrid crystal as an efficient, reusable and environmentally friendly heterogeneous catalyst for Knoevenagel condensation and synthesis of biscoumarin derivatives

A simple, effective, green and nontoxic protocol was used for the Knoevenagel condensation and the biscoumarin derivatives synthesis. It have demonstrated that the use of a new hybrid crystal as a heterogeneous catalyst makes it possible to obtain several advantages such as: a short reaction time and exceptional catalytic activity. Furthermore, (N2H5)2SiF6 was examined for five successive cycles without significant loss of catalytic activity.

A review of the recent progress on heterogeneous catalysts for Knoevenagel condensation.

One of the most crucial attributes of synthetic organic chemistry is to design organic reactions under the facets of green chemistry for the sustainable production of chemicals. Thus, due to the intensified environmental and safety concern, the need for new technologies for conducting chemical transformation has grown. In this regard, there is enormous interest in the use of heterogeneous catalysts as they generally avoid the generation of waste, require fewer toxic reagents, as well as entail easier separation and recycling of the catalyst. α,β-Unsaturated acids have been widely used in various industrial applications and have been identified as one of the most promising chemicals obtained via the Knoevenagel condensation reaction. This review aims to discuss the most pertinent heterogeneous catalytic systems such as zeolites, mesoporous silica, ionic liquids, metal oxides, and graphitic carbon nitride-based catalysts in the Knoevenagel reaction. Ultimately, this review focuses not only on the catalyst but also provides an overall idea and guide for the preparation of new catalysts with outstanding properties by looking at the chemical and engineering aspects such as the reaction conditions and the mechanisms.

Synthesis, characterization of polystyrene-phosphate films and their application as heterogeneous catalyst for Knoevenagel condensation in solvent-free conditions

Novel film catalysts of the polystyrene (Ps) and trimethyl phosphate (P) nanoparticles were synthesized on glass substrates by soft chemistry using doctor blade method. Subsequently, the prepared Ps–P film catalysts were characterized by various techniques, including fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), density (d), polarizing microscope (PM), X-ray diffraction (XRD) and thermal analysis. According to the results, the structure and morphology of film catalysts were confirmed by all analyses. The Ps–P films, as heterogeneous solid catalysts, have demonstrated strong activity for Knoevenagel condensation, producing alkenes of high purity. The recovered yields are excellent, up to 96% in solvent-free conditions at room temperature. Further, the film catalysts have showed high stability, good reusability (up to five times) while maintaining their efficiency and productivity. In the present study, the polystyrene/phosphate film catalysts were characterized and synthesized by soft chemistry method. These film catalysts were show an excellent catalytic activity for Knoevenagel condensation reaction. Further, they have demonstrated high yields, in solvent-free at room temperature, with a good reusability and high stability.

A new 2D cadmium coordination polymer based on hydroxyl‐substituted benzenedicarboxylic acid as an effective heterogeneous catalyst for Knoevenagel condensation

A self‐assembled new 2D cadmium network, [Cd (BDC‐OH)(DMF)2·DMF]n (Cd‐BDC‐OH), was synthesized based on 2‐hydroxyterephthalic acid (BDC‐OH) ligand and utilized as a heterogeneous catalyst for Knoevenagel condensation. The structure was fully elucidated by single‐crystal X‐ray diffraction, Hirshfeld surface analysis, powder X‐ray diffraction, field emission‐scanning electron microscopy, Fourier transform‐infrared spectroscopy and thermogravimetric analysis. The fabricated coordination polymer exhibited high catalytic activity under ambient conditions, and was used without significant drop in product yield in further cycles.

Polyamine-functionalized carbon dots as active catalyst for Knoevenagel condensation reactions

In this study, carbon dots coated with diluted polyethylene imine was prepared from the carbonization of citric acid (CA) with branched polyethylene imine (BPEI) at temperature (200 °C), designated as BPEI-CDs. The solid catalyst was characterized by various techniques including X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR), atomic force microscopy (AFM), high resolution transmission electron microscopy (HRTEM). The obtained BPEI-CDs are spherical graphite nanocrystals (averaging 5–10 nm). It was found that it could be used as heterogeneous catalyst for Knoevenagel condensation of aromatic aldehydes with malononitrile at 60 °C in ethanol. The Knoevenagel aromatic products were obtained with a moderate to excellent conversion within 2 h. The BPEI-CDs as catalyst was easily isolated from the reaction mixtures by simple filtration and reused for three times without significant loss of catalytic activity. There was also no contribution from the leached active species and conversion was only being possible in the presence of the prepared modified carbon dots.

A facile microwave-assisted Knoevenagel condensation of various aldehydes and ketones using amine-functionalized metal organic frameworks

An amine-functionalized metal organic framework (MOF) was used as highly efficient and recyclable heterogeneous catalyst for Knoevenagel condensation of various aromatic aldehydes and ketones in ethanol. The catalytic efficiency was demonstrated by the high conversion of the reactants with 100% selectivity under microwave (µW) irradiation, while dramatically reduced the reaction time as compared to the conventional heating method. Importantly, the MOF maintained its structural integrity after catalytic reactions and it could be reused several times without remarkable loss of activity.

Chitosan as a biodegradable heterogeneous catalyst for Knoevenagel condensation between benzaldehydes and cyanoacetamide

A natural biopolymer chitosan is being employed as heterogeneous solid base catalyst for the Knoevenagel condensation reaction between benzaldehydes and cyanoacetamide under mild reaction conditions. This reaction offers the direct synthesis of condensation product with two functional groups that can readily be functionalized. The biopolymer is used for five cycles with no decrease in activity and hot filtration test proves heterogeneity of the reaction. Some of the salient features of this strategy include biodegradability of catalyst, high catalyst stability, mild reaction conditions and wide substrate scope. The structural integrity is retained even after repeated cycles as evidenced by powder X-ray diffraction (XRD).

An in situ approach to functionalize metal-organic frameworks with tertiary aliphatic amino groups.

Metal-catalyzed reductive amination of formyl-containing linkers with N,N-dialkylformamide solvents is concomitant with the solvothermal coordination assembly, leading to novel MOFs functionalized with tertiary aliphatic amino groups. This illustrates a novel one-pot strategy to functionalize MOFs through in situ organic transformation. The UiO-66 MOFs partially functionalized with the amino groups are highly active heterogeneous catalysts for Knoevenagel condensation.

A functionalized UiO-66 MOF for turn-on fluorescence sensing of superoxide in water and efficient catalysis for Knoevenagel condensation.

In the present work, a new MOF material of the UiO-family called Zr-UiO-66-NH-CH2-Py (1) has been obtained by the solvothermal technique and successfully characterized. The MOF structure was assembled with 2-((pyridin-4-ylmethyl) amino) terephthalic acid (H2BDC-NH-CH2-Py) as linker and Zr4+ ion. The activated form of 1 (called 1') exhibits considerable thermal and chemical stability. Compound 1' showed a very rapid and selective response for the fluorometric sensing of superoxide (O2·-) in aqueous medium even in the presence of the potentially competitive reactive oxygen species (ROS). The limit of detection value for O2·- sensing is 0.21 μM, which is comparable with those of the reported O2·- sensors. This is the first MOF based fluorescent sensor for the detection of O2·-. The response time of this MOF sensor for O2·- is very short (240 s). On the other hand, 1' was employed as a solid heterogeneous catalyst for Knoevenagel condensation between benzaldehyde and ethyl cyanoacetate at 80 °C in ethanol resulting in a very high yield of the desired product. The effects of the esterified linker ((CH3)2BDC-NH-CH2-Py) and the corresponding metal salt (ZrCl4) on this catalytic reaction were examined separately. We have also tested the substrate scope elaborately for the catalytic reaction promoted by catalyst 1'.