SO3H-Functionalized Epoxy-Immobilized Fe3O4 Core-Shell Magnetic Nanoparticles as an Efficient, Reusable, and Eco-Friendly Catalyst for the Sustainable and Green Synthesis of Pyran and Pyrrolidinone Derivatives

A SO₃H-functionalized epoxy-immobilized Fe₃O₄ core-shell magnetic nanocatalyst was prepared through a simple three-step procedure, and it was identified by various analyses such as Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), differential thermal gravity (DTG), Brunauer-Emmett-Teller (BET) analysis, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA), vibration sample magnetometry (VSM), and powder X-ray diffraction (PXRD). BET analysis showed that the as-prepared nanocatalyst was synthesized with a mesoporous structure and high specific area (35.45 m² g^-1). The TEM image clearly showed that the particle size distribution was in the range of 47-65 nm. The designed magnetic nanocatalyst was used successfully in the synthesis of pyran derivatives via the reaction of dimedone, malononitrile, and various aromatic aldehydes and synthesis of pyrrolidinone derivatives via the reaction of various aromatic aldehydes, aniline, and diethyl acetylenedicarboxylate. The nanocatalyst was simply isolated from the reaction mixture utilizing an external magnet and reused several times according to the model reactions without significant loss in its efficiency.

Novel Magnetically-Recoverable Solid Acid Catalysts with a Hydrophobic Layer in Protecting the Active Sites from Water Poisoning

Three novel magnetically-recoverable solid acid catalysts (hydrophobic catalysts Fe3O4@SiO2-Me&PrSO3H, Fe3O4@SiO2-Oc&PrSO3H and hydrophilic catalyst Fe3O4@SiO2-PrSO3H) were synthesized by introducing organic propylsulfonic acid and alkyl groups to Fe3O4@SiO2 nanocomposites. We characterized these catalysts by FT-IR, EDS, XRD, VSM and SEM, and found that they had excellent core-shell structure and magnetic responsiveness. We also explored the impact of surface hydrophobicity on activity and stability of catalysts in ethyl acetate (EAC) synthesis reaction. The results indicated that: for reactivity and reusability, Fe3O4@SiO2-Oc&PrSO3H > Fe3O4@SiO2-Me&PrSO3H > Fe3O4@SiO2-PrSO3H. This was because octyl and methyl groups could build a hydrophobic layer on the surfaces of Fe3O4@SiO2-Oc&PrSO3H and Fe3O4@SiO2-Me&PrSO3H, and this could effectively prevent water molecules from poisoning active sites; the hydrophobicity of octyl was stronger than methyl. Fe3O4@SiO2-Oc&PrSO3H also showed higher catalytic activity in the external aqueous reaction system, which indicated that it had good water toleration. Moreover, we could easily separate Fe3O4@SiO2-Oc&PrSO3H from the reaction mixture with an external magnetic field, in the meanwhile, its reactivity could still remain above 80% after reusing 6 times.

Nanostructured silicate catalysts for environmentally benign Strecker-type reactions: status quo and quo vadis

Chemical processes are usually catalytic transformations. The use of catalytic reagents can reduce the reaction temperature, decrease reagent-based waste, and enhance the selectivity of a reaction potentially avoiding unwanted side reactions leading to green technology. Chemical processes are also frequently based on multicomponent reactions (MCRs) that possess evident improvements over multistep processes. Both MCRs and catalysis tools are the most valuable principles of green chemistry. Among diverse MCRs, the three-component Strecker reaction (S-3-CR) is a particular transformation conducive to the formation of valuable bifunctional building blocks (α-amino nitriles) in organic synthesis, medicinal chemistry, drug research, and organic materials science. To be a practical synthetic tool, the S-3-CR must be achieved using alternative energy input systems, safe reaction media, and effective catalysts. These latter reagents are now deeply associated with nanoscience and nanocatalysis. Continuously developed, nanostructured silicate catalysts symbolize green pathways in our quest to attain sustainability. Studying and developing nanocatalyzed S-3-CR condensations as an important model will be suitable for achieving the current green mission. This critical review aims to highlight the advances in the development of nanostructured catalysts for technologically important Strecker-type reactions and to analyze this progress from the viewpoint of green and sustainable chemistry.

Recent progress in the applications of silica-based nanoparticles

Functionalized silica nanoparticles (SiO2 NPs) have attracted great attention due to their promising distinctive, versatile, and privileged physiochemical characteristics. These enhanced properties make this type of functionalized nanoparticles particularly appropriate for different applications. A lack of reviews that summarizes the fabrications of such nanomaterials and their different applications in the same work has been observed in the literature. Therefore, in this work, we will discuss the recent signs of progress in the fabrication of functionalized silica nanoparticles and their attractive applications that have been extensively highlighted (advanced catalysis, drug-delivery, biomedical applications, environmental remediation applications, and wastewater treatment). These applications have been selected for demonstrating the role of the surface modification step on the various properties of the silica surface. In addition, the current challenges in the applications of functionalized silica nanoparticles and corresponding strategies to discuss these issues and future perspectives for additional improvement have been addressed.

Synthesis and Biological Properties of Coumarin Analogue: A Brief Review

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One of the most prominent aromatic organic chemical compound is Coumarin having formula C9H6O2 which is widely known for its benefits in drug industry. Colourless crystalline solid having sweet scent is coumarin’s physical identity. It serves various purposes such as in synthesis of medicines, laser dyes, perfumes and many more. Having enormous usages it becomes important to synthesize such compound so various reactions were performed in order to obtain coumarins. This review explicates the preparation of coumarin by Pechmann Condensation and its biological characteristics.

A review on convenient synthesis of substituted coumarins using reuseable solid acid catalysts

Due to growing concern about chemicals and their impact on the environment, cleaner reaction conditions are needed to be incorporated into chemical synthetic procedures. Recently, the use of heteropolyacid catalysts, mainly reuseable solid acid catalysts, has gained a leading role in organic synthesis due to their environmental and economic considerations and industrial utilization. The high catalytic activity, moisture sensitivity, reusability and inexpensive makes solid supported reagents attractive substituents to conventional Lewis acids. Nowadays synthesis of coumarins and their derivatives has attracted considerable attention from organic and medicinal chemists for many years as a large number of natural products contain this heterocyclic nucleus. In continuation with our investigations into the synthesis of substituted coumarins and due to several advantages of heterogeneous catalysts viz. cost-effective, no side products, high yield of desired products and no toxic waste material, here we report a new approach for the synthesis of substituted coumarins using solid acid catalysts.

Magnetic Nanoparticle Composites: Synergistic Effects and Applications

Composite materials are made from two or more constituent materials with distinct physical or chemical properties that, when combined, produce a material with characteristics which are at least to some degree different from its individual components. Nanocomposite materials are composed of different materials of which at least one has nanoscale dimensions. Common types of nanocomposites consist of a combination of two different elements, with a nanoparticle that is linked to, or surrounded by, another organic or inorganic material, for example in a core-shell or heterostructure configuration. A general family of nanoparticle composites concerns the coating of a nanoscale material by a polymer, SiO2 or carbon. Other materials, such as graphene or graphene oxide (GO), are used as supports forming composites when nanoscale materials are deposited onto them. In this Review we focus on magnetic nanocomposites, describing their synthetic methods, physical properties and applications. Several types of nanocomposites are presented, according to their composition, morphology or surface functionalization. Their applications are largely due to the synergistic effects that appear thanks to the co-existence of two different materials and to their interface, resulting in properties often better than those of their single-phase components. Applications discussed concern magnetically separable catalysts, water treatment, diagnostics-sensing and biomedicine.

Green Conversion of Saponins to Diosgenin in an Alcoholysis System Catalyzed by Solid Acid Derived from Phosphorus Tailings

This work proposed to prepare solid acid from phosphorus tailings and successfully convert Dioscorea zingiberensis C.H. Wright (DZW) into diosgenin from the perspective of solid waste resource reuse and clean production. The results showed that SiO₂-SO₃H solid acid could catalyze the production of diosgenin from total saponins under solvothermal reaction conditions. In addition, the parameters of a single factor, such as the amount of SiO₂-SO₃H, solvent volume, reaction temperature, and reaction time, were optimized to confirm the optimal range of reaction conditions, and the optimal process conditions were determined by the response surface method. The yield of diosgenin was 2.45 ± 0.17% under the optimum conditions, and the yield of diosgenin was increased by 12.90% compared with the traditional acid hydrolysis process. Except the relatively higher catalytic activity, the alcoholysis approach for the production of diosgenin has no waste liquid to discharge. The products were analyzed by high-performance liquid chromatography-mass spectrometry, and the pathway to convert total saponins into diosgenin under SiO₂-SO₃H has been proposed. Moreover, the adopted catalyst can be prepared with very low cost from phosphorus tailings. Considering the obvious superiorities, the alcoholysis approach in this work could be a promising strategy for green production of diosgenin as well as a possible utilization pathway of phosphorus tailings.

Fe3O4@C@OSO3H as an efficient, recyclable magnetic nanocatalyst in Pechmann condensation: green synthesis, characterization, and theoretical study

Novel sulfonated carbon-coated magnetic nanoparticles (SCCMNPs; Fe₃O₄@C@OSO₃H) were designed, synthesized, characterized, and applied as an efficient nanocatalyst for green synthesis of coumarin derivatives through Pechmann condensation. The Fe₃O₄@C@OSO₃H was manufactured through a simple and inexpensive two-step procedure and characterized by FTIR, EDX, XRD, SEM, TEM, DLS, VSM, and TGA techniques. It was identified as an efficient heterogeneous catalyst in the Pechmann condensation of phenol derivatives and β-ketoesters, leading to high-yield coumarin derivatives under solvent-free conditions. The Fe₃O₄@C@OSO₃H removed after reaction finishing point by an external magnet, and it was reused fifteen times at the same conditions. Besides, theoretical studies were carried out using B3LYP/6-311++G(d,p) to more consideration of the reaction mechanism. The study of the frontier molecular orbitals, NBO atomic charges, molecular electrostatic potential of reactants, as well as Pechmann condensation mechanism was known very useful in suitable reactant choice. The reaction was performed through the electrophilic attack, dehydration, and trans-esterification, respectively.

Magnetic iron oxide/phenylsulfonic acid: A novel, efficient and recoverable nanocatalyst for green synthesis of tetrahydrobenzo[b]pyrans under ultrasonic conditions

A novel magnetic iron oxide supported phenylsulfonic acid (Fe₃O₄@Ph-SO₃H) with core-shell structure is prepared, characterized and applied as efficient nanocatalyst for green synthesis of tetrahydrobenzo[b]pyrans. The Fe₃O₄@Ph-SO₃H was prepared via modification of magnetic iron oxide cores with 1,4-bis(triethoxysilyl)benzene (BTEB) followed by sulfonation of aromatic rings. The Fe₃O₄@Ph-SO₃H was characterized using FTIR, TGA, PXRD, SEM, TEM, VSM and EDX techniques. This was effectively applied for synthesis of tetrahydrobenzo[b]pyrans in water as green solvent at room temperature under ultrasonic conditions. The products were obtained in high to excellent yields at short times. The recoverability, reusability and durability of this nanocatalyst were studied under applied reaction conditions.

Cellulose sulfonic acid as a green, efficient, and reusable catalyst for Nazarov cyclization of unactivated dienones and pyrazoline synthesis

A high yielding and eco-friendly procedure for the preparation of cyclopentenoid and pyrazoline derivatives via cellulose sulfonic acid-mediated electrocyclization processes.