The Efficient Knoevenagel Condensation Promoted by Bifunctional Heterogenized Catalyst Based Chitosan-EDTA at Room Temperature

Synthetic strategy for multimodal -NH2 functionalized chitosan-based materials towards sustainable evolution

Chitosan, a very significant carbohydrate backbone, possesses a distinct ability for functionalization. Due to its unique ability to assemble physically and chemically, chitosan has tunable structural features in the direction of versatile, sustainable applications. Here, a simple free amino group (-NH2) within the carbo backbone of chitosan has been considered to develop chitosan-modified materials or hydrogels. Aromatic moieties have their specific functions, which makes them valuable. However, their pungent smells, insolubility in water, toxicities, and price make them challenging to use as native in specific applications. Here, a detailed sketch for chitosan, functionalized with a few aromatic moieties, is described to show how simple synthetic approaches synergistically move towards eco-friendly applications.

CdS/CeO2/Ag2CO3 nanocomposite as an efficient heterogeneous catalyst for Knoevenagel condensation and acetylation reactions

Knoevenagel condensation and acetylation reactions play a critical role in organic synthesis by facilitating the formation of carbon-carbon bonds and the modification of functional groups; however, limitations like low efficiency and demanding reaction conditions and time underscore the necessity for developing better techniques to enhance their practical applications. In this study, a ternary nanocomposite of CdS/CeO2/Ag2CO3 was synthesized by varying the molar ratio of CdS to CeO2/Ag2CO3 using the precipitation method. This heterogeneous catalyst was developed for Knoevenagel condensation and acetylation reactions applications. The optical properties, functional groups, crystalline structure, morphology, and surface area of the synthesized catalysts were characterized using UV-Vis-DRS, FTIR, XRD, SEM, and N2 adsorption-desorption isotherms, respectively. For the Knoevenagel condensation reaction between benzaldehyde and malononitrile, the optimal conditions were found to be the use of water as a solvent, at 10% w/w catalyst loading based on the total reagent mass, and room temperature (20 °C). Under these conditions, CdS/CeO2/Ag2CO3 with a CdS: CeO2/Ag2CO3 weight ratio of 3:1 gave high yields, 92.19 ± 0.41 in 33 min for Knoevenagel condensation and 93.8 ± 1.19 in just 3 min for the acetylation reaction. The reaction conditions were tested for different aromatic aldehydes with malononitrile, yielding high isolated products. The reusability of the CdS/CeO2/Ag2CO3 (3:1) catalyst was assessed, with only a 6.4% decrease in yield after sixth consecutive runs under optimal reaction conditions. Furthermore, the optimized catalyst, CdS/CeO2/Ag2CO3 (3:1), was evaluated for its catalytic activity in the acetylation of an aniline derivative. The structures of the synthesized products, 2-benzalidinemalononitrile and acetanilide, were confirmed by spectrometric techniques such as1H-NMR,13C-NMR, and FTIR analysis.

Larvicidal potential of Knoevenagel adducts against Aedes aegypti: theoretical study and in vitro validation

AIM

This study investigated the larvicidal potential of Knoevenagel adducts against Aedes aegypti larvae to develop sustainable alternatives for controlling disease vectors like dengue.

METHODS

Larvicidal activity of Knoevenagel adducts (1a-l) was evaluated on fourth-stage Aedes aegypti larvae. Additional analyses included nitric oxide measurement, cell profiling, toxicity assessment, molecular docking, molecular dynamics simulation, and ADMET (Absorption, Distribution, Metabolism, and Toxicity) evaluation.

RESULTS

Compounds 1c and 1g showed high larvicidal efficacy, with LC50 values of 3.39 and 5.13 ppm. Hemolymph analysis revealed altered hemocyte composition, indicating an immune response, though nitric oxide levels remained unchanged. Molecular docking identified strong interactions between the Aedes aegypti FKBP12 enzyme (PDB: 3UQI) and Knoevenagel adducts. Compound 1g had the highest activity probability and binding affinity, while 1c showed strong interactions validated by biological assays. Molecular dynamics confirmed stable interactions of 1c and FKBP12, with both 1c and 1g displaying significant van der Waals contributions. ADMET analysis highlighted 1c as a less toxic compound, with minimal mutagenic risk, favorable pharmacokinetics, and high bioavailability.

CONCLUSIONS

Knoevenagel adducts 1c and 1g are promising candidates for effective, selective, and environmentally friendly larvicides.

Ultrasound-Promoted preparation and application of novel bifunctional core/shell Fe3O4@SiO2@PTS-APG as a robust catalyst in the expeditious synthesis of Hantzsch esters

In this work, D-(-)-α-phenylglycine (APG)-functionalized magnetic nanocatalyst (Fe₃O₄@SiO₂@PTS-APG) was designed and successfully prepared in order to implement the principles of green chemistry for the synthesis of polyhydroquinoline (PHQ) and 1,4-dihydropyridine (1,4-DHP) derivatives under ultrasonic irradiation in EtOH. After preparing of the nanocatalyst, its structure was confirmed by different spectroscopic methods or techniques including Fourier transform infrared (FTIR) spectroscopy, energy-dispersive X-ray spectroscopy (EDS), field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and thermal gravimetric analysis (TGA). The performance of Fe₃O₄@SiO₂@PTS-APG nanomaterial, as a heterogeneous catalyst for the Hantzsch condensation, was examined under ultrasonic irradiation and various conditions. The yield of products was controlled under various conditions to reach more than 84% in just 10 min, which indicates the high performance of the nanocatalyst along with the synergistic effect of ultrasonic irradiation. The structure of the products was identified by melting point as well as FTIR and ¹H NMR spectroscopic methods. The Fe₃O₄@SiO₂@PTS-APG nanocatalyst is easily prepared from commercially available, lower toxic and thermally stable precursors through a cost-effective, highly efficient and environmentally friendly procedure. The advantages of this method include simplicity of the operation, reaction under mild conditions, the use of an environmentally benign irradiation source, obtaining pure products with high efficiency in short reaction times without using a tedious path, which all of them address important green chemistry principles. Finally, a reasonable mechanism is proposed for the preparation of polyhydroquinoline (PHQ) and 1,4-dihydropyridine (1,4-DHP) derivatives in the presence of Fe₃O₄@SiO₂@PTS-APG bifunctional magnetic nanocatalyst.

Chitin and Silk Fibroin Biopolymers Modified by Oxone: Efficient Heterogeneous Catalysts for Knoevenagel Reaction

New materials from silk fibroin (FS-Ox) and chitin (CT-Ox) functionalized with Oxone® salt were developed for application in the synthesis of Knoevenagel adducts. The experiments were performed using benzaldehyde derivatives, malononitrile, and a mixture of water and ethanol as green solvents. The efficiency of conventional and microwave irradiation as heating sources for this reaction was also investigated. When the reactions were performed for 60 min under optimized conditions with conventional heating, twelve Knoevenagel adducts 2a–l were obtained, with good yields for both catalysts (CT-Ox 60–98% and FS-Ox 71–98%). When microwave irradiation was used, the reaction periods were reduced twelvefold, with the same Knoevenagel adducts with good CT-Ox (39–99%) and FS-Ox (35–99%) yields obtained in most cases. The reuse of these materials as catalysts in successive reactions was also evaluated, and CT-Ox FS-Ox were successfully used for 4 and 2 cycles, respectively. The results presented prove the efficiency of the CT-OxFS-Ox catalyst as a promising low-cost and reusable material with suitable catalytic properties to be applied in the aldol condensation reaction in a sustainable way.