The direct three-component condensation of 6aminouracil, 6-amino-2-thiouracil or 6-amino-1,3dimethyluracil, with arylaldehydes and malononitrile to generate a series of pyrido[2,3-d]pyrimidine derivatives has been carried out over nanocrystalline MgO with high efficiency in water as a green solvent at 80°C. The morphology and structure of the nanocrystalline MgO were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The results confirmed the nanocrystalline MgO particle size is approximately 50 nm. This methodology offers significant improvements for the synthesis of pyrido[2,3-d]pyrimidine derivatives with regard to the yield of products, simplicity in operation, and green aspects by avoiding toxic catalysts and solvents.
2]. Furthermore, enhancing the percentages of exposed highly reactive facets, at nanoscale, does improve the efficiency of materials in various applications such as photocatalysis and dye-sensitized solar cells [3]. By presenting individual properties, nanoparticles can become a kind of structure unit, in other words, "artificial atoms" to conduct a new type of materials which have difficult in estimating collective properties [4]. Through green nanotechnology, we can get contrivable nanomaterial that contains unique characters which bulk materials never have [5]. This means that we are creating materials with good catalytic activity, stability and more selectivity via changing their forms, sizes and morphologies [6]. Applications of nanoparticles in catalytic reactions are because as size decreases, the surface area-to-volume ratio increases, which enhanced interaction between the reactant and the catalyst, which are needed for high catalytic efficiencies [7]. Unsupported nanoparticles are often less stable, and usually coagulation is inevitable during the catalytic reactions [8]. To generate stable nanoparticles with good activity, stabilizing the surface is required. Protection has been performed by the addition of polymers or longchain alkyl surfactants with polar functional groups that attached to the nanoparticle surface via covalent or electrostatic interactions [9, 10]. Alternatively, nanoparticles have been immobilized or grafted onto inorganic supports to improve their stabilization and recycling ability [12]. Progress in the discovery of new support materials for the heterogenization of homogeneous catalysts has been periodically reviewed [13]. In this article, the green catalytic processes and recent advances in organic transformations catalyzed by magnetically retrievable catalysts (MRCs) are highlighted. Prior to this, methods for the synthesis of catalysts immobilized on magnetic nanoparticles will be addressed briefly.Abstract Unsupported nanoparticles are often less stable, and usually coagulation is unavoidable during the catalytic reactions. To generate stable nanoparticles with good activity, stabilizing the surface is required. Protection has been performed by the addition of polymers or long-chain alkyl surfactants with polar functional groups that attached to the nanoparticle surface via covalent or electrostatic interactions. Alternatively, nanoparticles have been immobilized or grafted onto inorganic supports to improve their stabilization and recycling ability. In this article, the green catalytic processes and recent advances in organic transformations catalyzed by magnetically retrievable catalysts are reviewed. Prior to this, methods for the synthesis of catalysts immobilized on magnetic nanoparticles are addressed briefly.
In this study, a series of elastomeric nanocomposites based on specific amounts of polyamide6 (PA6)/chloroprene rubber (CR) blends which are compatibilized with ethylene propylene diene monomer-grafted-maleic anhydride (EPDM-g-MA) and different amounts of graphene oxide (GO) were prepared with melt mixing method. The effect of compatibilizer and reinforcement concentration in the PA6/CR blend matrix was investigated using theoretical and experimental analysis. Dispersion of nanoplatelets within rubber blend matrix was proven with transmission electron microscopy and field emission-scanning electron microscopy. The modified microstructure of samples showed the significant effect of EPDM-g-MA and GO on the size reduction of CR droplets in the PA6 continuous phase. The results from differential scanning calorimetry and dynamic mechanical thermal analysis revealed the effect of EPDM-g-MA and GO as an effective nucleating agent in PA6-enriched GO/CR (PA6EGO/CR). The findings obtained from thermogravimetric analysis displayed that the GO in the presence of an EPDM-g-MA as a compatibilizer can cause a higher thermal stability in PA6EGO/CR. From mechanical properties, by adding a compatibilizer to the PA6/CR blend, the tensile strength changed from 39.0 to 45.1, the Young's modulus altered from 522.2 to 716.0 and the elongation at break changed from 246.8 to 222.2. While incorporation of 5 phr of GO to the compatibilized blend, the tensile strength increased by 25.2%, the Young's modulus increased by 36.6% and the elongation at break decreased by 20%. The Christensen-Lo model used for analyzing the
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