Catalyst For Aldol Reaction Research Articles

Microwave assisted Schiff base metal complexes as potential anticancer and antimicrobial agents: A critical review

Schiff bases are organic compounds which contain azomethine group (-C=N-) by reacting primary amines and carbonyl compounds. The presence of an azomethine group in the Schiff base facilitates coordination with transition metal ions. The term Schiff base is normally applied to these compounds when they are being used as ligands to form coordination complexes with metal ions. Such complexes occur naturally, but the majority of Schiff bases are artificial and are used to form many important catalysts. Schiff base metal complexes prepared using microwave irradiation have gained more attention because of their excellent strategy in generating quick and stable products in higher yields by improving the speed of reaction with lesser energy and exhibits various biological activities including antifungal, antibacterial, anti-tubercular, antiviral, antimalarial, anti-diabetic, anticancer, antioxidant, antidiuretic, anti-inflammatory, antipyretic and anti-HIV agents. Apart from biological applications, they are also used as a catalyst in Aldol reactions, polymerization reactions, oxidation reactions and other chemical reactions. Imine-ligand containing transition metal complexes including copper, zinc and cadmium, have proven to be effective starting points for the synthesis of metal or metal chalcogenide nanoparticles. In this review, various metal complexes derived from Schiff bases synthesised using microwave approaches are discussed along with their antibacterial, antifungal and anticancer activities.

Caesium carbonate functionalized magnetic nanoparticles: An efficient heterogeneous and reusable inorganic catalyst for aldol reaction in water

Caesium carbonate functionalized magnetic nanoparticles: An efficient heterogeneous and reusable inorganic catalyst for aldol reaction in water

Biomass waste-derived recyclable heterogeneous catalyst for aqueous aldol reaction and depolymerization of PET waste

Eco-friendly biomass waste-derived recyclable heterogeneous catalyst for aldol reaction in water and for methanolysis of PET waste.

Amyloid Peptide Mixtures: Self-Assembly, Hydrogelation, Nematic Ordering, and Catalysts in Aldol Reactions.

Morphological, spectroscopic, and scattering studies of the self-assembly and aggregation of mixtures of [RF]4 and P[RF]4 peptides (where R = arginine; F = phenylalanine; P = proline), in solution and as hydrogels, were performed to obtain information about polymorphism. CD data confirmed a β-sheet secondary structure in aqueous solution, and TEM images revealed nanofibers with diameters of ∼10 nm and micrometer lengths. SAXS curves were fitted using a mass fractal-component and a long cylinder shell form factor for the liquid samples, and only a long cylinder shell form factor for the gels. Increasing the P[RF]4 content in the systems leads to a reduction in cylinder radius and core scattering density, suggesting an increase in packing of the peptide molecules; however, the opposite effect is observed for the gels, where the scattering density is higher in the shell for the systems containing higher P[RF]4 content. These compounds show potential as catalysts in the asymmetric aldol reactions, with cyclohexanone and p-nitrobenzaldehyde in aqueous media. A moderate conversion (36.9%) and a good stereoselectivity (69:31) were observed for the system containing only [RF]4. With increasing P[RF]4 content, a considerable decrease of the conversion was observed, suggesting differences in the self-assembly and packing factor. Rheological measurements were performed to determine the shear moduli for the soft gels.

Assessing the Recyclability of Supramolecularly Assembled Organocatalytic Species: A Theoretical Insight

AbstractAsymmetric organocatalytic synthesis is a powerful tool in organic chemistry to achieve desired stereoisomers in high purity via mild catalytic routes. The immobilization of homogeneous catalytic species onto heterogeneous phases embodies the evolution of asymmetric catalysis, since it allows the recycling of the catalyst for several runs until degradation. Previously reported non‐covalent immobilization of proline‐based catalysts for aldol reaction onto magnetic nanoparticles functionalized with β‐cyclodextrin (MNP‐β‐CB) demonstrated the viability of the methodology. This paper proposes two new catalyst recycling strategies based on Cucurbit[7]uril (CB[7]) for the aldol reaction and the Robinson annulation. These recycling methodologies are conceptually different. The former relies on the homogeneous encapsulation of the catalyst in cucurbituril, CB[7] ⋅ Cat, and its recycling in the aqueous phase by extraction of the aldol product with organic solvents. The latter relies on the heterogeneous encapsulation of the catalyst as MNP‐CB[7] ⋅ Cat2 system and its recycling by magnetic harvesting. Density functional theory (DFT) calculations have been employed to rationalize the thermodynamics of experimental results, and to suggest caveats and plausible improvements in view of a future catalytic design.

Asymmetric Direct Aldol Reaction in Confined Space: Molecular Conformations of Organocatalyst Affect Chiral Induction

AbstractWe have demonstrated that chiral induction in the aldol product is possible by generating an enzyme‐like cavity in molecular framework of the amphiphlic catalyst. The esters of trans‐4‐hydroxy‐L‐proline and long chain fatty acids have been synthesized by O‐acylation. Synthesized molecules were used as organocatalysts for asymmetric direct aldol reaction between 4‐nitrobenzaldehyde and cyclohexanone. The molecular framework of the catalyst not only induces the amphiphilicity but also acquires specific conformation leads to formation of catalytic cavity facilitating stereo‐induction in the aldol product. Systematic addition of olefinic bonds in the long hydrocarbon chain makes this cavity more robust stabilizing transition state of the aldol product. By proper tuning of the water content and % loading of the catalyst in aldol reaction, o/w or w/o type emulsion is formed due to aggregation of catalyst molecules. Performance based evaluation of catalytic activity suggests that aldol reaction proceeds with ∼ 99% yield, 84% dr and 97.94% ee in presence of 10% catalyst (having three π bonds), in an o/w emulsion (85 equiv. of water) within 12 h. The stereoselectivity of the catalyst is almost maintained up to 2.5% loading. The high stereoselectivity of the aldol reaction is maintained even on increasing the amount of water to 300 equiv. A plausible reason has been proposed for retaining the high stereoselectivity and corroborated by computational analysis.

Construction of Class I Aldolases-like Carboxyl-Controlled-Graphene Oxide Supported 3-Aminopropyl-triethoxysilane Heterogeneous Catalysts for Aldol Reaction

Designing catalysts that achieve the rates and selectivities of natural enzymes is a long-standing goal in synthetic chemistry. Herein, the carboxyl-controlled-graphene oxide supported 3-aminopropyl-triethoxysilane (GOn-APTS) heterogeneous catalyts like the class I aldolases with –NH2 and phenolic –OH groups were developed and applied in aldol reaction. The results demonstrate that the amount of –NH2 groups and phenolic –OH groups play important roles of activity and selectivity, respectively. The most efficiency catalyst GO8-APTS shows an excellent conversion of over 90% with a high aldol product selectivity of about 89%. Furthermore, the catalyst can be easily recovered and reused at least 5 times without significant loss of the reactivity.

L-Proline functionalized metal-organic framework PCN-261 as catalyst for aldol reaction

A homochiral MOF, PCN-261-NHPro, was prepared via solvothermal synthesis of Fe2CoO(CH3COO)6 with H3tcpb-NHPro. The aldol addition was selected as a model reaction for the estimation of the catalytic performance of the PCN-261-NHPro, which showed reversed diastereomeric selectivity in contrast to homogeneous catalysts.

Preparation of Ga₂O₃ Doped Sulfonated Tin Oxides as a Highly Active and Recyclable Heterogeneous Solid Acid Catalyst for Aldol Reactions.

Ga₂O₃ doped sulfonated tin oxide catalysts were prepared via co-condensation method in ethanol solvent, followed by sulfonation and calcination. The samples were characterized by isothermal nitrogen adsorption/desorption, powder X-ray diffraction (XRD), thermal gravimetric analysis (TG), Raman spectra and DRIFT spectra. The number of acid sites on the catalysts was measured with the potentiometric titration of butyl amine. The results showed that the addition of small amounts of Ga₂O₃ to sulfonated tin oxide resulted in an enhanced acid site density, which makes Ga₂O₃ doped sulfonated tin oxide catalysts highly active for aldol reactions. The catalyst containing 1.5% Ga₂O₃ exhibited much higher activity than those of SO₄²-/SnO₂, SO₄²-/ZrO₂ and H₃PO₄ in aldol condensation of prenal and prenol for citral precursor, which is a important in fragrance industry. Besides the high activity, the catalyst also exhibited good recyclability, making 1.5% GST an efficient and promising solid catalyst for aldol reactions.

Tetramethylguanidine-Functionalized Fe3O4/ Chloro-Silane Core-Shell Nanoparticles: an Efficient Heterogeneous and Reusable Organocatalyst for Aldol Reaction

Tetramethylguanidine supported onto magnetic Fe3O4 nanoparticles (MNPs-TMG) was prepared and identified by several techniques such as TEM, XRD, SEM, FT-IR and TGA analyses. The synthesized catalyst was utilized as an effective catalyst for aldol reaction between acetone and various aldehydes to achieve β-hydroxy carbonyl compounds in excellent yields. This procedure has several advantages, such as moderate reaction conditions, excellent yields, short reaction time and easy purification of the products. Additionally, supporting this organosuperbase catalyst on magnetic nanoparticles offers a simple method for easy reuse and recovery of the catalyst using an external magnetic field.

The role of water in the reusability of aminated silica catalysts for aldol reactions

The reusability of methylaminopropyl active sites grafted on mesoporous amorphous silica, either with cooperative silanol groups or trimethylsilated, was assessed in the aldol reaction of acetone with 4-nitrobenzaldehyde. Raman, 13C NMR, and UV–Vis spectroscopy demonstrated the presence of stable enamines on the spent catalysts. These enamines are produced as a side product from iminium intermediates in the catalytic cycle. Water co-feeding enhances the desorption of the iminium intermediates and, hence, suppresses the formation of these stable enamine species. The reusability of the cooperative catalyst increased to 70% with co-feeding 0.69 wt% water, while an almost complete reusability was achieved for the trimethylsilated catalyst. Continuous-flow experimentation showed that the cooperative effect of the silanol groups was lost during the first 7 h on-stream, yet activity losses continued, most likely due to silica hydrolysis. Activity losses persisted on the more hydrophobic trimethylsilated catalyst, but were significantly less pronounced.

Histidine-based copper tetrapeptides as enantioselective catalysts for aldol reactions.

Copper(ii)-peptides are widely used as industrial catalysts such as in the aerobic oxidation of organic molecules, formation of new C–H bonds and in the azide–alkyne cycloaddition reaction. The length of peptides and the effect of adding copper metal into peptides were questioned in their field of applications. Five novel histidine-based tetrapeptides with the sequences HAAD (P1), HAFD (P2), HAVD (P3), AGHD (P4) and PGHD (P5) were synthesized using the solid phase peptide scheme and analysed with high performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS) with percentage purities as high as 99.5%. All the peptides were positively charged (+1) and the molecular weight calculated from m/z values of MS results coincided with the theoretical molecular weight of the peptides. Copper(ii)-peptides derived from these peptides and copper(ii) acetate monohydrate (CuP1–CuP5) in a 1 : 2 ratio was synthesised, purified and characterised by ultraviolet-visible spectroscopy (UV-Vis), ultraviolet-fluorescence spectroscopy (fluorescence) and fourier transform infrared spectroscopy (FTIR), circular dichroism spectroscopy (CD) and optical rotation polarimetry. It provided the necessary information on the secondary structure and the successful binding of copper(ii) to the specific amino acids, hence leading to the putative geometry of copper(ii)-peptides and the difference in the chirality of amino acids, peptides and copper(ii)-peptides. The catalytic activities of the synthesised complexes were evaluated. CuP1 & CuP3 catalysed both the asymmetric aldol reactions with high enantioselectivity of p-nitrobenzaldehyde with cyclohexanone (% ee = 87.3 & 80.3, respectively) and of p-anisaldehyde with cyclohexanone (% ee = 95.5 & 90.9, respectively).

Design of thermoresponsive poly(ionic liquid) gels containing proline units to catalyse aldol reaction in water

Ionic liquid monomers and a proline-containing monomer were copolymerised in the presence of cross-linker to form ionic liquid polymer gels that show lower critical solution temperature-type phase change in water. The obtained gels were utilised as catalysts for aldol reaction in water. Since proline-catalysed aldol reaction is composed of three equilibrium steps including dehydration condensation reaction and hydrolysis reaction, yield of product was affected by the water content around the proline unit in the gel. Since thus prepared ionic liquid polymer gels showed the thermo-responsive change in water content, the product yield was found to be affected by the temperature around the phase transition temperature.

Aldol Reactions by Lipase From Rhizopus niveus, an Example of Unspecific Protein Catalysis

The lipase from Rhizopus niveus (RNL) catalyzed by unspecific protein catalysis the aldol reactions between cyclohexanone and aromatic aldehydes in organic solvents with water or aqueous buffer solution. The reactional conditions strongly influenced the yield (0–99%) and enantioselectivities in the anti-products (6–55% ee anti ). The aldol products with enantioselectivities in the anti-product were observed for inactive enzyme and in denaturing conditions. Therefore, the reactions in the evaluated conditions proceeded by unspecific protein catalysis with moderate enantioselectivities and not by promiscuous activity. These enzymatic studies identify a new green catalyst for aldol reactions and new possibilities for lipases, especially for the use of the lipase RNL, which has been scarcely reported in the literature and catalyzed the aldol reaction between different aromatic aldehydes and cyclohexanone.

1,1,3,3-Tetramethylguanidine immobilized on graphene oxide: A highly active and selective heterogeneous catalyst for Aldol reaction

Developing efficient catalysts with high yields of aldol products in the aldol reaction is of great importance and remains a challenge. By a facile route utilizing hydrogen bonding, 1,1,3,3-tetramethylguanidine was successfully loaded on graphene oxide to afford a immobilized catalyst. This immobilized catalyst shows an excellent conversion of 97.3% with a high aldol product selectivity of 92.5% in the aldol reaction of p-nitrobenzaldehyde with acetone, which is superior to the corresponding homogeneous catalyst with a conversion of 97.1% and selectivity of only 59.5% under similar conditions. Furthermore, the immobilized catalyst can be easily recovered and reused without significant loss of the reactivity.

Nanoparticle Based on Poly(Ionic Liquid) as an Efficient Solid Immobilization Catalyst for Aldol Reaction and Multicomponent Reaction in Water.

An environmentally friendly nanoparticle-supported catalyst was successfully prepared via in situ ionic complexation between imidazolium-based polymer ionic liquid (PIL) and poly(l-prolinamide-co-MAA). The physical and chemical properties of the obtained nanoparticles were characterized by TEM, FTIR, XPS, and static water contact angle experiments. The surface properties of the nanoparticle were found to significantly affect the catalytic performance. The nanoparticle with PIL outer facilitated the adsorption of reaction substrate in it. As a result, the catalytic system catalyzed the asymmetric Aldol reaction and multicomponent reaction in pure water efficiently. The catalytic system was able to be reused and recycled five times, and with no discernible loss in catalytic activity and enantioselectivity. These findings suggest that nanoparticles based on PIL may provide a new approach for preparing high performance supported catalysts for organic reactions in water. This technology also addresses issues associated with mass transfer in pure water reactions.

ChemInform Abstract: Review of the Aldol Reaction

AbstractReview: 126 refs.

Multifunctional heterocyclic scaffolds for hybrid Lewis acid/Lewis base catalysis of carbon–carbon bond formation

Several new classes of hybrid catalysts have been synthesized by tethering heterocyclic metal (Lewis acid) chelating scaffolds to several different amines capable of facilitating enamine catalysis. Oxazole, thiazole, and imidazole-based chiral precatalysts were prepared in several steps from amino acid starting materials, and these were combined with a variety of metal Lewis acids for potential use as catalysts for various carbon–carbon bond formations. Air- and moisture-tolerant catalysts for enantioselective direct aldol reactions with activated benzaldehyde acceptors were identified, with optimal results obtained with proline-derived oxazole–carboxamide precatalysts combined with Zn(OTf)2 or lanthanide (III) salts. Control studies support the hypothesis that these act as unimolecular hybrid catalysts for the aldol reaction of propionaldehyde and 4-nitrobenzaldehyde.

Zinc complexes formed by 2,2′-bipyridine and 1,10-phenanthroline moieties combined with 2-azanorbornane: modular chiral catalysts for aldol reactions

Zinc complexes of new hybrid chiral imine ligands based on a bicyclic skeleton appear to be effective modular catalysts in asymmetric aldol reactions.

The Persian Gulf Calcined Coral, Acropora Species: An Efficient Catalyst for Aldol Condensation

Background: Coral, a marine organism, is known for its unique solid, natural, and efficient catalyst in organic reactions. Calcium carbonate (CaCO 3 ), the main component of marine coral, is an efficient, basic, and natural solid for catalytic aldol condensation reaction of aldehydes and ketones having α-hydrogens to produce β-hydroxy carbonyl compounds with good yields at room temperature. Objectives: The purpose of this research was to study using calcined coral as an efficient catalyst for aldol reaction at room temperature. Materials and Methods: Marine coral (Acropora sp.) was washed several times using methanol-ethyl acetate and deionized water and then dried in an oven at 80°C for 48 hours. The dried coral was ground to get fine powder. For preparation of calcined coral, its powder was put in an oven at 800°C for 2 hours. Calcined coral and sodium nitrate (1:1) were well stirred in sufficient water for about 5 hours. Then, the mixture was calcined in an oven at 800°C for 2 hours. In general experiment, the reaction was carried out by mixing aldehyde (150 mmol), ketone (50 mmol), 0.1 g of calcined coral/sodium nitrate, 5 mL water-ethanol (1:1) as a solvent. Finally, the mixture was stirred at room temperature for the appropriate time. Results: The best conditions for condensation reaction are using the calcined coral/sodium nitrate, as a catalyst in the presence of ethanol/water at room temperature. Aldol condensation reaction of nitro-substituted benzaldehydes with ketones has greater yields than benzaldehydes. Electron-withdrawing groups such as NO 2 on benzaldehyde ring activate aldol condensation reaction. In comparison, 4-methoxybenzaldehyde reacts more slowly with ketones and decreases the yield of products. Conclusions: Calcined coral/sodium nitrate as a new, efficient, and natural heterogeneous catalyst used in aldol condensation reaction of ketones and aldehydes led to β-hydroxyketones in good to high yields in appropriate condition.