Synthesis, characterization and catalytic application of a novel ethyl and boron sulfonic acid based bifunctional periodic mesoporous organosilica

Magnetic yolk-shell structured periodic mesoporous organosilica supported palladium as a powerful and highly recoverable nanocatalyst for the reduction of nitrobenzenes

A novel palladium-loaded yolk-shell structured nanomaterial with magnetite core and phenylene-based periodic mesoporous organosilica (PMO) shell (Fe3O4@YS-Ph-PMO/Pd) nanocatalyst was synthesized for the reduction of nitrobenzenes. The Fe3O4@YS-Ph-PMO/Pd was prepared through cetyltrimethylammonium bromide (CTAB) directed condensation of 1,4-bis(triethoxysilyl)benzene (BTEB) around Fe3O4@silica nanoparticles followed by treatment with palladium acetate. This nanocatalyst was characterized by using Fourier transform infrared (FT-IR) spectroscopy, thermal gravimetric analysis (TGA), low-angle and wide-angle powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) analyses. These analyses showed a magnetic nanomaterial with high chemical and thermal stability for the designed composite. The Fe3O4@YS-Ph-PMO/Pd nanocomposite was employed as a powerful and highly recoverable catalyst in the green reduction of nitroarenes in H2O at room temperature. A variety of nitroarene derivatives were applied as substrate in the presence of 0.9 mol% of Fe3O4@YS-Ph-PMO/Pd catalyst. All nitroarenes were selectively converted to their corresponding amines with high to excellent yields (92-96%) within short reaction times (10-18 min). This catalyst was recovered and reused at least 11 times without significant decrease in efficiency and stability.

A novel heterogeneous biocatalyst based on graphene oxide for synthesis of pyran derivatives

Graphene oxide modified with tryptophan (GO-Trp) has been introduced as a new heterogeneous acid-base biocatalyst for synthesis of some pyran derivatives. GO was prepared according to the Hummer's method and tryptophan as a low-cost green amino acid is covalently bonded to the surface of GO without any organic or toxic reagents in a green way. The new catalyst was characterized by different spectroscopic methods such as Fourier transform infrared, X-ray diffraction (XRD), etc. …. The results of XRD patterns showed an increase in the distance between the GO plates in the presence of the modifying agent which specifies the presence of amino acid between the GO layers. XPS analysis also confirmed successful modification through the presence of C-N bonds in the structure of the catalyst. In addition, improvements in thermal stability and changes in the morphology of the samples were observed using thermogravimetric analysis and Field emission scanning electron microscopy analysis respectively. Evaluation of the catalyst performance in the synthesis of some benzo[b]pyran and pyrano[3,2-c] chromene derivatives showed presentable results. Seven benzo[b]pyran (4a-4g) and five pyrano[3,2-c] chromene (4h-4l) derivatives were synthesized. GO-Trp as a safe, natural and efficient catalyst, could be reused up to 5 runs for synthesis of pyran derivatives without any significant decrease in its potency. High purity of the products and desirable yields are other points that make the present work more attractive.

Magnetic silica/graphene oxide nanocomposite supported ionic liquid-manganese complex as a powerful catalyst for the synthesis of tetrahydrobenzopyrans

A novel magnetic silica/graphene oxide nanocomposite supported ionic liquid/manganese complex (Fe3O4@SiO2-NH2/GO/IL-Mn) is prepared, characterized and its catalytic application is investigated. The Fe3O4@SiO2-NH2/GO/IL-Mn catalyst was synthesized via chemical immobilization of graphene oxide on Fe3O4@SiO2 nanoparticles followed by modification with ionic liquid/Mn complex. This nanocomposite was characterized by using SEM, TGA, FT-IR, PXRD, EDX, TEM, nitrogen adsorption-desorption, and VSM analyses. The catalytic application of Fe3O4@SiO2-NH2/GO/IL-Mn was studied in the synthesis of tetrahydrobenzo[b]pyrans (THBPs) in water solvent at RT. This nanocatalyst was successfully recovered and reused at least eight times without a significant decrease in its activity.

Magnetic ethylene-based periodic mesoporous organosilica supported palladium: An efficient and recoverable nanocatalyst for Suzuki reaction

In the present study, a novel magnetic ethylene-based periodic mesoporous organosilica supported Pd-Schiff base complex (Fe₃O₄@PMO/SB-Pd) was prepared, characterized and applied as a recoverable nanocatalyst for green synthesis of Suzuki products. Chemical composition, magnetic and thermal behavior, morphology and particle size of Fe₃O₄@PMO/SB-Pd were investigated by using FT-IR, TGA, EDX, VSM, PXRD, TEM and Scanning electron microscopy (SEM) analyses. The Fe₃O₄@PMO/SB-Pd nanocomposite was applied as an efficient nanocatalyst in the Suzuki reaction under ultrasonic conditions giving corresponding products in high yield. Some advantages of this study are simple purification of products, the use of water solvent, easy catalyst separation, short reaction time and high catalyst efficiency and recoverability.

Functionalized Silicas for Metal-Free and Metal-Based Catalytic Applications: A Review in Perspective of Green Chemistry

Heterogeneous catalysis plays a key role in promoting green chemistry through many routes. The functionalizable reactive silanols highlight silica as a beguiling support for the preparation of heterogeneous catalysts. Metal active sites anchored on functionalized silica (FS) usually demonstrate the better dispersion and stability due to their firm chemical interaction with FSs. Having certain functional groups in structure, FSs can act as the useful catalysts for few organic reactions even without the need of metal active sites which are termed as the covetous reusable organocatalysts. Magnetic FSs have laid the platform where the effortless recovery of catalysts is realized just using an external magnet, resulting in the simplified reaction procedure. Using FSs of multiple functional groups, we can envisage the shortened reaction pathway and, reduced chemical uses and chemical wastes. Unstable bio-molecules like enzymes have been stabilized when they get chemically anchored on FSs. The resultant solid bio-catalysts exhibited very good reusability in many catalytic reactions. Getting provoked from the green chemistry aspects and benefits of FS-based catalysts, we confer the recent literature and progress focusing on the significance of FSs in heterogeneous catalysis. This review covers the preparative methods, types and catalytic applications of FSs. A special emphasis is given to the metal-free FS catalysts, multiple FS-based catalysts and magnetic FSs. Through this review, we presume that the contribution of FSs to green chemistry can be well understood. The future perspective of FSs and the improvements still required for implementing FS-based catalysts in practical applications have been narrated at the end of this review.