Showing papers on "Knoevenagel condensation published in 2014"
TL;DR: Porous functionalized 3D COFs could be a promising new class of shape-selective catalysts in base-catalyzed Knoevenagel condensation reactions, according to their remarkable conversion and high size selectivity.
Abstract: The design and synthesis of 3D covalent organic frameworks (COFs) have been considered a challenge, and the demonstrated applications of 3D COFs have so far been limited to gas adsorption. Herein we describe the design and synthesis of two new 3D microporous base-functionalized COFs, termed BF-COF-1 and BF-COF-2, by the use of a tetrahedral alkyl amine, 1,3,5,7-tetraaminoadamantane (TAA), combined with 1,3,5-triformylbenzene (TFB) or triformylphloroglucinol (TFP). As catalysts, both BF-COFs showed remarkable conversion (96% for BF-COF-1 and 98% for BF-COF-2), high size selectivity, and good recyclability in base-catalyzed Knoevenagel condensation reactions. This study suggests that porous functionalized 3D COFs could be a promising new class of shape-selective catalysts.
529 citations
TL;DR: In this paper, the authors summarized various methods for the synthesis of coumarins via Knoevenagel condensation, including mild, efficient, and environmentally friendly protocols with good yield and purity.
172 citations
TL;DR: The amine-functionalized graphene oxide (OFGO) was used as an acid-base bifunctional catalyst in one-pot cascade reactions containing successive acetal hydrolysis and Knoevenagel condensation.
Abstract: The amine-functionalized graphene oxide was prepared by a facile one-step silylation approach and used as an acid–base bifunctional catalyst in one-pot cascade reactions containing successive acetal hydrolysis and Knoevenagel condensation owing to the separate coexistence of original carboxylic acid on the edge of the GO sheet and the postgrafted amine groups on the GO basal surface. This catalyst exhibited much higher activity than either amine-functionalized active carbon, amine-functionalized SBA-15, or amine-functionalized Al2O3 due to the enriched surface acid sites and the diminished diffusion limitation as well as high catalyst dispersion in liquid solution due to the unique two-dimensional structure. More importantly, this catalyst could be easily recycled and used repetitively, showing potential application in industry.
152 citations
TL;DR: A metal-free three-component reaction to synthesize 1,4,5-trisubstituted 1,2,3-triazoles from readily available building blocks, such as aldehydes, nitroalkanes, and organic azides, is described, and the products are obtained with high yield and regioselectivity.
Abstract: A metal-free three-component reaction to synthesize 1,4,5-trisubstituted 1,2,3-triazoles from readily available building blocks, such as aldehydes, nitroalkanes, and organic azides, is described. The process is enabled by an organocatalyzed Knoevenagel condensation of the formyl group with the nitro compound, which is followed by the 1,3-dipolar cycloaddition of the azide to the activated alkene. The reaction features an excellent substrate scope, and the products are obtained with high yield and regioselectivity. This method can be utilized for the synthesis of fused triazole heterocycles and materials with several triazole moieties.
150 citations
TL;DR: In this paper, the amino functionalized metal-organic framework of Zr(IV) with 2-aminoterephthalate, UiO-66-NH2, was studied as a solid catalyst for Knoevenagel condensation.
Abstract: The amino-functionalized metal–organic framework of Zr(IV) with 2-aminoterephthalate, UiO-66-NH2, was studied as a solid catalyst for Knoevenagel condensation. The material can efficiently catalyze the condensation reaction of benzaldehyde with ethyl cyanoacetate or malononitrile in highly polar solvents such as DMF, DMSO and ethanol. The catalytic system has also been tested for various aromatic aldehydes, the conversion easily reaching more than 90% under mild conditions. It was demonstrated that the catalytic process is heterogeneous and shows size effects, characteristic of a porous catalyst. The catalyst can be recycled without losing its framework integrity and catalytic activity. The catalytic activity has been compared with dimethyl 2-aminoterephthalate and the isostructural amino-free MOF (UiO-66). The superior performance of UiO-66-NH2 has been attributed to the site-isolated acid–base bifunctional character. It has been proposed that the Zr site in close proximity to the amino group activates aldehydes to promote the formation of aldimine intermediates from the aldehydes and the amino group.
146 citations
TL;DR: In this paper, a multifunctional carbazole-based conjugated microporous polymer MFCMP-1 is successfully prepared by oxidative coupling polymerization using a single monomer and structurally characterized.
Abstract: A multifunctional carbazole-based conjugated microporous polymer MFCMP-1 is successfully prepared by oxidative coupling polymerization using a single monomer and structurally characterized. A new three-dimensional π-conjugated polymer framework can be combined with permanent microporous, highly luminescent properties and abundant nitrogen activated sites in the skeleton. It possesses a large BET surface area of over 840 m2 g−1 with a pore volume of 0.52 cm3 g−1, and displays a high carbon dioxide uptake capacity (up to 3.69 mmol g−1) at 273 K and 1 bar, with good selectivity towards CO2 over N2 and CH4. MFCMP-1 exhibits also strong fluorescent emission at 529 nm after excitation at 380 nm in THF solution and works as a luminescent chemosensor towards hazardous and explosive molecules, such as nitrobenzene, 2-nitrotoluene, and 2,4-dinitrotoluene. In addition, MFCMP-1 features a high concentration of Lewis base nitrogen sites on its internal surfaces; it thus acts as a highly efficient recyclable heterogeneous organocatalyst towards Knoevenagel reaction of malononitrile with aromatics, heterocyclic aldehydes, and cyclic ketones. Furthermore, we further highlight that the ease of synthesis and low cost, coupled with multifunctional properties, make MFCMP-1 an attractive functional material in practical applications.
132 citations
TL;DR: For the first time Am-MOP with basic functional groups has been exploited for the Knoevenagel condensation reaction between aldehydes and active methylene compounds and enhanced catalytic efficiency and high selectivity for small substrate molecules.
Abstract: We report the design and synthesis of an amide functionalized microporous organic polymer (Am-MOP) prepared from trimesic acid and p-phenylenediamine using thionyl chloride as a reagent. Polar amide (CONH) functional groups act as a linking unit between the node and spacer and constitute the pore wall of the continuous polymeric network. The strong covalent bonds between the building blocks (trimesic acid and p-phenylenediamine) through amide bond linkages provide high thermal and chemical stability to Am-MOP. The presence of a highly polar pore surface allows selective CO2 uptake at 195 K over other gases such as N-2, Ar, and O-2. The CO2 molecule interacts with amide functional groups via Lewis acid base type interactions as demonstrated through DFT calculations. Furthermore, for the first time Am-MOP with basic functional groups has been exploited for the Knoevenagel condensation reaction between aldehydes and active methylene compounds. Availability of a large number of catalytic sites per volume and confined microporosity gives enhanced catalytic efficiency and high selectivity for small substrate molecules.
120 citations
TL;DR: A series of BF2 complexes of hydrazine-Schiff base linked bispyrrole have been prepared from a simple two-step reaction from commercially available substances and are highly fluorescent in solution, film, and solid states with larger Stokes shift and excellent photostabilities comparable or even super to those of their BODIPY analogues.
113 citations
TL;DR: In this article, the effect of basicity of porous metal-carboxylates, such as MIL-100(Al), Cu3(BTC)2·(H2O)3, UiO-66 and amino-modified Ui-66-NH2 on their catalytic performance, was studied in the Knoevenagel condensation of benzaldehyde with malonitrile to 2-benzylidenemaloninitrile.
109 citations
TL;DR: Simple cinnamic acids synthesized by Knoevenagel condensation reactions were evaluated and proved to be the most potent LOX inhibitor, and Phenyl- substituted acids showed better inhibitory activity against soybean LOX.
Abstract: Cinnamic acids have been identified as interesting compounds with antioxidant, anti-inflammatory and cytotoxic properties. In the present study, simple cinnamic acids were synthesized by Knoevenagel condensation reactions and evaluated for the above biological activities. Compound 4ii proved to be the most potent LOX inhibitor. Phenyl- substituted acids showed better inhibitory activity against soybean LOX, and it must be noted that compounds 4i and 3i with higher lipophilicity values resulted less active than compounds 2i and 1i. The compounds have shown very good activity in different antioxidant assays. The antitumor properties of these derivatives have been assessed by their 1/IC50 inhibitory values in the proliferation of HT-29, A-549, OAW-42, MDA-MB-231, HeLa and MRC-5 normal cell lines. The compounds presented low antitumor activity considering the IC50 values attained for the cell lines, with the exception of compound 4ii. Molecular docking studies were carried out on cinnamic acid derivative 4ii and were found to be in accordance with our experimental biological results.
108 citations
TL;DR: In this article, the effect of N-donor ligands with diverse basicity in the Knoevenagel condensation reaction was investigated and it was shown that increasing the basicity of ligands leads to an improvement in catalytic activity.
Abstract: Three 3D, porous Zn(II)-based metal–organic frameworks, TMU-4, TMU-5 and TMU-6, containing azine-functionalized pores, were readily and quickly prepared via mechanosynthesis. Catalytic performance of these MOFs and the effect of N-donor ligands with diverse basicity in the Knoevenagel condensation reaction are investigated. Increasing the basicity of N-donor ligands leads to improvement in catalytic activity. Results show that among the three compounds, TMU-5 has the highest catalytic activity upon increasing its basicity of azine function in the N-donor ligand. These catalysts maintain their crystalline framework after the reaction and are easily recycled.
TL;DR: In this paper, a novel molecular size and shape-selective catalyst, microporous metal-organic framework HKUST-1 immobilized amino-functionalized basic ionic liquid (ABIL-OH), was synthesized by facile impregnation and activation.
Abstract: A novel molecular size- and shape-selective catalyst, microporous metal-organic framework HKUST-1 immobilized amino-functionalized basic ionic liquid (ABIL-OH), was synthesized by facile impregnation and activation. Characterizations and catalytic results revealed that the catalytically active species ABIL-OH could be confined in well-defined HKUST-1 nanocavities via Cu NH2 coordination bond. The resulting ABIL-OH/HKUST-1 heterogeneous catalyst showed comparable catalytic activity and enhanced selectivity in liquid phase Knoevenagel condensation, and it could be recovered conveniently and reused at least 5 times without significant loss of its catalytic efficiency. Moreover, ABIL-OH/HKUST-1 catalyst demonstrated distinct size- and shape-selective properties for discrimination of reactants in Knoevenagel condensation. It was supposed that diffusion kinetics of reactants might be controlling step and play a more important role than the nature of the substituents in the confined microenvironment.
TL;DR: In this paper, the Bronsted acidic imidazolium-based metal-free and halogen-free ionic liquid hydrogen sulfate was immobilized on nanoporous silica SBA-15.
Abstract: The Bronsted acidic imidazolium-based metal-free and halogen-free ionic liquid hydrogen sulfate was immobilized on nanoporous silica SBA-15. The structures of synthesized catalysts were investigated using different characterization techniques, including FT-IR, small angle XRD, SEM, TEM and TGA. The [MPIm][HSO4]@SBA-15 is used as an alternative to conventional catalysts in the Knoevenagel-Michael-cyclization processes for the synthesis of tetrahydrochromenes and hexahydroquinoline carboxylates via a multicomponent procedure. The reaction time is reduced drastically and the reaction is progressed in an environmentally friendly way. The immobilized catalyst can be recycled without substantial loss of activity after seven runs. (C) 2014 Elsevier B.V. All rights reserved.
TL;DR: Graphene oxide (GO) acts as a highly active heterogeneous base catalyst for a wide variety of reactions as discussed by the authors, and the catalytic activities of GO in the condensation reaction of various substituted benzaldehydes with acetophenone and with active methylene compound malononitrile (Knoevenagel reaction) at room temperature under solvent free condition.
Abstract: Graphene oxide (GO) acts as a highly active heterogeneous base catalyst for a wide variety of reactions. Here we have described the catalytic activities of GO in the condensation reaction of various substituted benzaldehydes with acetophenone (aldol condensation) and with active methylene compound malononitrile (Knoevenagel reaction) at room temperature under solvent free condition. GO is characterized by powder X-ray diffraction (XRD), UV–visible spectra, Fourier transform infrared spectroscopy (FT-IR) and AFM. The experimental results showed that the GO had higher catalytic activity and it can be recycled without significant loss of its activity.
TL;DR: An efficient solvent-free protocol for the synthesis of tetrahydrobenzo[b]pyrans by the condensation of malonitrile, dimedone and various aldehydes in the presence of acetic acid functionalized imidazolium salts was reported in this article.
Abstract: An efficient solvent-free protocol for the synthesis of tetrahydrobenzo[b]pyrans by the condensation of malononitrile, dimedone and various aldehydes in the presence of acetic acid functionalized imidazolium salts (1-carboxymethyl-3-methylimidazolium bromide {[cmmim]Br} and 1-carboxymethy1-3-methylimidazolium tetrafluoroborate {[cmmim][BF4]}) as reusable catalysts has been reported. The turn over frequency (TOF) values of the catalysts are higher than some of the previously reported catalysts. Also, thermal gravimetric analysis (TGA), differential thermal gravimetry (DTG), X-ray diffraction analysis (XRD) and calculations of the size and inter-planer distance of the catalysts have been reported in this work.
TL;DR: A new non-interpenetrating 3D metal-organic framework built from nickel(ii) ions as connectors and methanetetrabenzoate ligands (MTB(4-)) as linkers has been synthesized and characterized and straightforward dependence of the substrate conversion on the size of used aldehyde was established.
Abstract: 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 (MTB4−) 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 A2, 9.4 × 8.0 A2, 12.6 × 11.7 A2 and 14.9 × 14.9 A2, 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 m2 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 MTB4− 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 MTB4− containing a metal–organic framework was proposed.
TL;DR: A series of benzofuran-2-carboxamides of biological and medicinal significance were synthesized by a microwave-assisted one-pot parallel approach via O-alkylation/Knoevenagel condensation as mentioned in this paper.
TL;DR: Reversible switching between two states of the triangular nanoswitch [Cu(1)](+) was accomplished by alternate addition of 2-ferrocenyl-1,10-phenanthroline (2) and copper(I) ions to allow alternating on/off switching of two orthogonal catalytic processes.
Abstract: Reversible switching between two states of the triangular nanoswitch [Cu(1)]+ was accomplished by alternate addition of 2-ferrocenyl-1,10-phenanthroline (2) and copper(I) ions. The two switching states regulate the binding and release of two distinct catalysts, piperidine and [Cu(2)]+, in a fully interference-free manner and allow alternating on/off switching of two orthogonal catalytic processes. In switching state I, piperidine is released from the nanoswitch and catalyzes a Knoevenagel addition between 4-nitrobenzaldehyde and diethyl malonate (ON-1 and OFF-2), while in state II the released [Cu(2)]+ catalyzes a click reaction between 4-nitrophenylacetylene and benzylazide (OFF-1 and ON-2). Upon addition of one equivalent of 2 to the (OFF-1 and ON-2)-state, both catalytically active processes are shut down (OFF-1 and OFF-2).
TL;DR: In this article, the authors reported the development of tri-lacunary polyoxometalates (POMs) of Na8H[A]-PW9O34]·7H2O and Na8 H[B-PW 9O 34]·19H 2O as highly selective and efficient heterogeneous base catalysts.
Abstract: We reported for the first time the development of tri-lacunary polyoxometalates (POMs) of Na8H[A-PW9O34]·7H2O and Na8H[B-PW9O34]·19H2O (Na-A-PW9 and Na-B-PW9) as highly selective and efficient heterogeneous Lewis base catalysts for Knoevenagel condensation, cyanosilylation of various aldehydes and ketones and the synthesis of benzoxazole derivatives at 25 °C under mild conditions. Since both Na-A-PW9 and Na-B-PW9 display no characteristic porosity, it is proposed that the catalytic reactions proceed not only on the surface and interface, but also in the bulk phase. The catalysts can be easily recovered and reused for at least six times without obvious decrease of catalytic activities and the structures of the catalysts remain unchanged after recycling. The easy preparation, high efficiency, reusability of the heterogeneous catalysts of Na-A-PW9 and Na-B-PW9 exhibit great potential for further application.
TL;DR: In this paper, an efficient solvent-free approach for the synthesis of 2-amino benzo[h]chromene derivatives from the condensation of malonitrile, 2-naphthol and various aldehydes using acetic acid functionalized imidazolium salt (1-carboxymethyl-3-methylimidazolate bromide {[cmmim]Br} as a reusable catalysts is reported.
TL;DR: In this paper, four basic ionic liquids (ILs), based on 1,4-diazobicyclo[2.2] octane (DABCO) and 3-chloro-1,2-propanediol, have been introduced as catalysts for Knoevenagel condensation.
Abstract: Four novel basic ionic liquids (ILs), based on 1,4-diazobicyclo[2.2.2]octane (DABCO) and 3-chloro-1,2-propanediol, have been introduced as catalysts for Knoevenagel condensation. These catalysts are applicable to a wide range of aromatic/heteroaromatic aldehydes with α-aromatic (heteroaromatic or polyaromatic)-substituted methylene compounds in water at room temperature, and they afford the products in excellent yields within short times. These reactions are operationally simple, and the desired products can be separated directly from the reaction mixture without further purification. A possible reaction mechanism was proposed, and the relevant evidence was given. In addition, the ionic liquids used can be regenerated and recycled several times without significant loss of activity. Furthermore, the novel ILs could be efficiently used in a step of atorvastatin synthesis.
TL;DR: In this article, a mesoporous silica with alternating hydrophobic and hydrophilic blocks was synthesized to promote heterogeneous asymmetric catalysis in the direct aldol reaction and the Knoevenagel-Michael cascade reaction.
Abstract: Promotion of heterogeneous asymmetric catalysis is of major interest in the asymmetric catalysis field. In this work, a novel strategy for the synthesis of l-proline-grafted mesoporous silica with alternating hydrophobic and hydrophilic blocks to promote the heterogeneous asymmetric catalysis was reported. The surface synergies in the neat environment and the interface acceleration in aqueous medium thereby fostered high catalytic activities and enantioselectivity in the direct aldol reaction and the Knoevenagel–Michael cascade reaction. The l-proline loading could be reduced to as low as 0.63 mol %, giving 95% ee for anti-isomers and 81% ee for syn-isomers in the catalytic asymmetric aldol reaction of nitrobenzaldehyde and cyclohexanone, which was hard to accomplish on the homogeneous counterpart. In the direct asymmetric aldol reaction of ethyl-2-oxoacetate and cyclohexanone, 82% yield in 24 h and 90% ee were achieved. More exciting, the catalysts were applied to more exigent reactions. As an example, i...
TL;DR: In this paper, a porphyrin-based conjugated microporous polymer with rich nitrogen sites in the skeleton has been synthesized by alkyne-alkyne homocoupling reaction.
Abstract: A new porphyrin-based conjugated microporous polymer with rich nitrogen sites in the skeleton has been synthesized by alkyne–alkyne homocoupling reaction. The Brunauer–Emmett–Teller specific surface area up to 662 m2 g−1 was obtained for the new polymer framework with a pore volume of 0.55 cm3 g−1. The polymer network displays high carbon dioxide uptake capacity (up to 3.58 mmol g−1) at 273 K and 1 bar, with good selectivity towards CO2 over N2 and CH4. Furthermore, this framework also acts as a solid organocatalyst towards Knoevenagel reaction of malononitrile with aromatic, heterocyclic aldehydes, and cyclic ketones. The reaction afforded the corresponding products in excellent yields (up to 99%) with short times. Moreover, the heterogeneous catalyst was also found to exhibit an excellent recyclability (up to 10 times) without loss of efficiency.
TL;DR: The results showed that the mesoporous CND materials had graphitic-like structures and consisted of CN heterocycles, as well as amino groups, and demonstrated high and stable catalytic activities, owing to an abundance of basic sites.
Abstract: Assisted by a new dissolution procedure, dicyandiamide (DCDA), an environmentally benign and cheap precursor, has been employed for the synthesis of mesoporous carbon nitride (CN) materials through a nanocasting approach. The synthesized mesoporous materials possessed high specific surface areas (269-715 m(2) g(-1)) with narrow pore-size distributions (about 5 nm) and faithfully replicated the mesostructures of the SBA-15 and FDU-12 templates. Several characterization techniques, including XRD, SAXS, TEM, Raman and FTIR spectroscopy, XPS, and CO2-TPD, were used to analyze the physicochemical properties of these materials and the results showed that the mesoporous CND materials had graphitic-like structures and consisted of CN heterocycles, as well as amino groups. In a series of Knoevenagel condensation reactions, as exemplified by the reaction of various aldehydes and nitriles, these mesoporous CND materials demonstrated high and stable catalytic activities, owing to an abundance of basic sites.
TL;DR: In this paper, a one-pot reaction system was developed by utilizing a bifunctional metal-organic framework photocatalyst (Zr-MOF-NH2), which promoted sequential photocatalytic oxidation and Knoevenagel condensation reaction to produce benzylidenemalononitrile from benzyl alcohol and malononitriles under UV-light irradiation.
TL;DR: In this paper, a new method has been developed for generating highly dispersed base sites on metal-organic framework (MOF) lattices, where the defect sites generated via this activation act as new strong basic sites within the catalyst structure.
Abstract: A new method has been developed for generating highly dispersed base sites on metal–organic framework (MOF) lattices. The base catalytic activity of two alkaline earth MOFs, M2(BTC)(NO3)(DMF) (M = Ba or Sr, H3BTC = 1,3,5-benzenetricarboxylic acid, DMF = N,N-dimethylformamide) was studied as a function of their activation procedures. The catalytic activity in Knoevenagel condensation and Michael addition reactions was found to increase strongly with activation temperature. Physicochemical characterization using FTIR, 13C CP MAS NMR, PXRD, XPS, TGA-MS, SEM, EPR, N2 physisorption and nitrate content analysis shows that during activation, up to 85% of the nitrate anions are selectively removed from the structure and replaced with other charge compensating anions such as O2−. The defect sites generated via this activation act as new strong basic sites within the catalyst structure. A fluorescence microscopic visualization of the activity convincingly proves that it is exclusively associated with the hexagonal crystals, and that reaction proceeds inside the crystal's interior. Theoretical analysis of the Ba-material shows that the basicity of the proposed Ba2+–O2−–Ba2+ motifs is close to that of the edge sites in BaO.
TL;DR: In this article, the combination of these functionalized PPAFs was successfully applied as compatible heterogeneous catalysts for cascade reaction of hydrolysis of dimethoxymethylbenzene, acid catalyzed, and Knoevenagel catalyzed by base.
Abstract: Porous aromatic frameworks (PPAFs) prepared by microwave assisted synthesis can be easily functionalized to obtain solid acid (sulfonic acid) and base (primary amine) catalysts. This porous material demonstrated to be an excellent support of different functional groups. The combination of these functionalized PPAFs was successfully applied as compatible heterogeneous catalysts for cascade reaction of hydrolysis of dimethoxymethylbenzene, acid catalyzed, and Knoevenagel catalyzed by base. The advantages of this catalytic system are its easy synthesis, good catalytic activity, coexistence of incompatible functional groups in homogeneous conditions, with different acid/base ratio, and is recycled up seven times without significant loss of activity. Our concept can be extended to other various one-pot incompatible homogeneous systems and make a contribution toward the creation of environmentally inspired chemical processes through the promotion of multiple reactions in a single reactor.
TL;DR: In this paper, the authors employed a periodic model and density functional theory to explain the high catalytic activity and selectivity of the metal-organic framework (MOF) copper benzene-1,3,5-tricarboxylate (CuBTC) catalyst.
Abstract: The high catalytic activity and selectivity of the metal–organic framework (MOF) copper benzene-1,3,5-tricarboxylate (CuBTC) that are observed experimentally in the Knoevenagel reaction are explained on the basis of computational investigations by employing a periodic model and density functional theory. Three factors are responsible for the unusually high activity of CuBTC: One, CuBTC can act as a base, and the active methylene reactant is deprotonated, whereas a temporary defect in the framework is formed; two, the thus-formed defect, a Bronsted acid site, simultaneously activates the aldehyde; three, the reaction takes place on two adjacent Cu2+ sites (Lewis acid sites) that are separated by 8.2 A. The results reported herein show the great versatility of the CuBTC MOF catalyst, including its amphiphilic character and the concerted effect of nearby framework metal cations.
TL;DR: In this paper, the basicity of La2O3 and La(OH)3 is utilized for Knoevenagel and Hantzsch reactions, and the results reveal the prevalence of Eley-Rideal type adsorption where only one of the reactants is adsorbed.
Abstract: Combustion synthesized La2O3 and subsequently produced La(OH)3 are characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and Brunauer–Emmitt–Teller (BET) methods. The basicity of La2O3 and La(OH)3 is utilized for Knoevenagel and Hantzsch reactions. Reaction of aldehydes with suitable substrates containing active methylene groups led to Knoevenagel and Hantzsch products in good to excellent yields in organic solvents, water and under dry or solvent free conditions. Catalytic activity remains unchanged even after multiple (nine) cycles. Detailed mechanistic investigation using the simple adsorption reveals the prevalence of Eley–Rideal type adsorption where only one of the reactants is adsorbed for the reaction.