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  • Open access
  • 95 Reads
g-C3N4/Ni nanocomposite: an efficient and eco-friendly recyclable catalyst for the synthesis of quinoxalines

Nowadays, with increasing environmental concerns, the development of sustainable and friendly heterogeneous catalysts has attracted more and more attention in both the scientific and industrial communities. Hence, the use of nanocatalysts with well-defined structures, environmentally benign, high catalytic activity, and high chemical stability are desirable instead of corrosive and hazardous chemicals. In recent years, polymeric mesoporous graphitic carbon nitride (g-C3N4) has turned out to be a fascinating choice for catalyst or catalyst support due to the special physical and chemical properties, thermal stability, non-toxicity, unique electronic properties, and large surface area. The incorporation of nitrogen atoms in the carbon architecture of the g-C3N4 gives rise to the active chemical sites exposed on the surface. On the other hand, depositing metal nanoparticles onto g-C3N4 is an effective strategy to enhance the catalytic activity of g-C3N4. In the present study, g-C3N­/Ni as a recyclable, highly efficient heterogeneous catalyst with a good porous structure have been prepared and its catalytic activity was investigated for the synthesis of quinoxaline derivatives.

  • Open access
  • 121 Reads
ZrO2/g-C3N4 hybrid nanocomposite: an efficient and eco-friendly recyclable catalyst for the trimethylsilyl protection of hydroxyl groups and synthesis of a-aminophosphonates

Recently considerable attention has been devoted to heterogeneous catalysts. Generally, heterogeneous catalysts offer several advantages such as mild reaction conditions, high throughput and ease of work-up procedures. Among the heterogeneous catalysts investigated, polymeric mesoporous graphitic carbon nitrides (g-C3N4) has attracted much attention recently due to strong van der Waals interactions between the layers, g-C3N4 is chemically stable against acid, base and organic solvents and also thermogravimetric analysis (TGA) reveals that g-C3N4 is thermally stable even in air up to 600 oC, which can be attributed to its aromatic C-N heterocycles. More importantly, g-C3N4 is only composed of two earth-abundant elements: carbon and nitrogen. This not only suggests that it can be easily prepared at low cost, but also its properties can be tuned by simple strategies without significant alteration of the overall composition. The last approach is considered as the most efficient way to design of high-performance heterogeneous catalysts utilizing the g-C3N4 as catalyst support. An interesting phenomenon is that the modification is mainly focused on metal oxides. Zirconia (ZrO2) is a physically rigid material with chemical inertness. It has high resistance against attacks by acids, alkalis, oxidants and reductants. In this study, ZrO2/g-C3N4 hybrid nanocomposite has been shown to be an excellent catalyst for the conversion of alcohols and phenols into their corresponding trimethylsilyl ethers with hexamethyldisilazane (HMDS) under solvent-free condition and for the synthesis of a-aminophosphonates. In addition, the ZrO2/g-C3N4 can be easily recycled after separation from the reaction mixture without considerable loss in catalytic activity.

  • Open access
  • 98 Reads
Synthesis of small organic molecule based on malononitrile group toward green energy performance in organic photovoltaic solar cells

In the last centuries, human beings have sought to supply their energy. Energy from fossil fuels is recognized as a sources unrenewable energy. Recently, due to the reduction of unrenewable resources, increased greenhouse gas emissions and environmental pollution, and endangering human health, people beings are forced to replace non-renewable energy sources with renewable energy sources. The most important devices to convert solar energy into electrical energy are solar cells. Organic solar cells are a green class of solar cells. Although organic photovoltaic solar cells (OPVSCs) have lower returns than the first generation solar cells; but, due to low cost of fabrication, lightweight and good flexibility, have attracted a lot of attentions. In green OPVSCs construction, from small and large organic molecules based on donorـlinkersـacceptor have been used.

  • Open access
  • 114 Reads
Acid treatment of halloysite nanoclay: Eco-friendly heterogeneous catalyst for the synthesis of pyrrole derivatives

Halloysite is a two-layered aluminosilicate with a tube structure. The external surface and the internal of halloysite nanotubes (HNTs) are composed of silicon-oxygen tetrahedron and alumina oxygen octahedrons, respectively. The reaction of the acid with both the outer and inner surfaces of the nanotubes causes the AlO6 octahedral layers to dissolve and dealumination occurred. The acid treatment of halloysite has been used as a traditional chemical activation method for improving the performance of its catalytic activity. In continues to our research and due to the importance of pyrrole scaffold, herein, an efficient synthesis of pyrrole derivatives was carried out in the presence of a catalytic amount of acid treatment HNTs as a nanocatalyst in ethanol at room temperature in high yields. The solid nanocatalyst can be recovered easily and reused without any significant loss of the catalytic activity.

  • Open access
  • 95 Reads
Ionic liquids vs. microporous solids as reusable reaction media for the catalytic C–H functionalization of indoles with alcohols

High performance reusable catalysts and reaction media are evaluated for the green alkylation of indoles with alcohols under mild and solvent-free conditions. For a range of Brønsted and Lewis acid catalytic sites in different environments, such as inexpensive ionic liquids or microporous solids, we show a correlation between the acid strength and catalytic activity, achieving the highest turnovers reported for strong acid sites upon five reuses under mild conditions.

  • Open access
  • 70 Reads
Unexpected migration of benzoyl group in the synthesis of 3-benzoyl-2-phenylbenzofurans under Wittig conditions

3-Aroyl[b]benzofurans represent the structural cores of a large number of bioactive molecules in current pharmaceutical use or development. As a result, numerous approaches towards the synthesis of 3-acylbenzofurans have been disclosed in the literatura.

The Wittig reaction, is an easy procedure to the benzofuran ring system. In a previous paper Hercouet and Le Corre reported that the intramolecular condensation of o-acyloxybenzylidenetriphenylphosphoranes leads to the benzofuran in aprotic medium (toluene) or to acylated product in protic medium (t-BuOH).

We recently found that the reaction of the triphenylphosphonium salt and aroyl chlorides leads together with the expected benzofurans, also to 3-benzoyl-2-phenylbenzo[b]furans via ylide acylation under Wittig conditions. We hypothesised that the key intermediate that leads to the 3-benzoyl derivatives was the o-[(benzoyloxy)benzyl]-triphenyl-phosphoranes. It was therefore prepared starting from o-cresol, and reacted with benzoyl chloride using Et3N in aprotic solvent i.e. toluene. In contrast with Hercouet and Le Corre findings, we obtained the 3-benzoyl derivatives, thus confirming our hypothesis. However, when the o-(benzoyloxy)benzyl)-triphenyl-phosphonium salt was reacted with 4-nitrobenzoyl chloride, we unexpectedly observed the formation of two 3-acyl isomers, thus suggesting that the regioselective benzoyl group migration occurred in some extent.

Our results are of considerable interest not only because they get insights into the reactivity of o-acyloxybenzylidenetriphenylphosphoranes, but also because they allowed to discover a versatile and general approach to functionalized 3-benzoyl-2-phenylbenzo[b]furans.

  • Open access
  • 82 Reads
Lewis acid-mediated mono- and bis-addition of C-nucleophiles to 1,3-dioxolan-4-ones

The reactions of oxocarbenium cations with different types of C-nucleophiles is a convenient tool for building carbon-carbon bonds. Many examples of the generation of oxocarbenium cations from different types of five-, six-, and seven-membered ring acetals and related compounds have been reported. 1,3-Dioxolan-4-ones are readily available building blocks obtained by the condensation of carbonyl compounds with α-hydroxy carboxylic acids, including natural ones, such as malic, lactic, and mandelic acids. 1,3-Dioxolan-4-ones (the so-called Seebach chiral templates) have found widespread application in the preparation of chiral compounds. However, few examples of C-nucleophilic addition to the oxocarbenium cation generated from 1,3-dioxolan-4-ones under the action of Lewis acids are known. One of the most eco-friendly, lowest-cost, and most stable catalysts is FeCl3, which exhibits a high activity in the reactions of acetals with allylsilanes and silyl ketene acetals. Therefore, we focused our attention on FeCl3 when studying the reaction of 1,3-dioxolan-4-ones with different silicon-containing nucleophiles and 1-alkynes. We report examples of the Lewis acid-mediated reaction between 1,3-dioxolan-4-ones and C-nucleophilic reagents, which can result in either mono- and bis-addition depending on the nature of the nucleophile. For example, in the case of nucleophiles after addition of which a CH2 unit or carbon-carbon triple bond forms near the cationic site, the reaction terminates at the step of mono-addition. In the case where an aromatic ring is adjacent to the cationic site, the addition of the second nucleophile molecule then occurs.

  • Open access
  • 60 Reads
Kinetic Study of the epoxy system BADGE n=0/IPD/ABS

The main objective of this work is the study of the curing kinetics of the epoxy system formed by the epoxy resin Diglicil ether of bisphenol A, Isophorone Diamine Hardener , and the thermoplastic modification agent, Acrylonitrile butadiene styrene or ABS . The introduction of a third component, in this case ABS, has been carried out to improve the application of this system in waterproofing and in the use of paints, as well as for the improvement of the resistance to the impact of this type of systems. In addition the obtaining of a kinetic and of the respective parameters will allow to know the properties and the knowledge of possible applications in the industry.

In particular, it is intended to reach a kinetic equation that is capable of describing the variation of the reaction rate according to the degree of curing for the all range of conversions, starting from the model proposed by Kamal et al.

  • Open access
  • 64 Reads
Methanolysis of 2-cyanopyridine in the coordination sphere of manganese(II). The structure of Mn4L6Cl2 cluster (L = methyl picolinimidate)

Increased reactivities of molecules coordinated in metal complexes have wide applications in chemistry. The activation of ligands containing the nitrile group upon their coordination to a manganese ion has been exploited in addition reactions of nucleophiles such as amines, alcohols and water. The 2-cyanopyridine as a chelating bidentate ligand can be coordinated to manganese ion from two nitrogen atoms of pyridine ring and carbonitrile group in the presence of non-protonic solvents. The reaction of 2-cyanopyridine and Mn(II) in methanol solution led to the formation of a Mn4L6Cl2 cluster 1 containing O-methyl picolimidate as a ligand (L). The coordination of 2-cyanopyridine to the Mn(II) ion as a chelating bidentate ligand activated the CN triple bond which subsequently suffered a nucleophilic attack by CH3OH. Complex 1 was characterized by standard techniques including microanalysis, IR spectroscopy, ESI spectrometry, and magnetic susceptibility measurements. The crystal structure of 1 was determined by X-ray diffraction techniques, and the crystallographic studies revealed a planar-diamond array for 1 where the six monoanionic picolinimidates act as chelating ligands through the two nitrogen atoms.

  • Open access
  • 164 Reads
Preparation and Hydro-lipophilic Properties of Methoxylated and Methylated 1-Hydroxynaphthalene-2-Carboxanilides

A series of variously methoxylated and methylated N-aryl-1-hydroxynaphthalene-2-carboxanilides was prepared and characterized as potential anti-invasive agents. As it is known that lipophilicity significantly influences the biological activity of compounds, the hydro-lipophilic properties of these mono-, di- and tri-substituted 1-hydroxynaphthalene-2-carboxanilides are investigated in the study. All the discussed hydroxynaphthalene derivatives were analysed using the reversed-phase high performance liquid chromatography method to measure lipophilicity. The procedure was performed under isocratic conditions with methanol as an organic modifier in the mobile phase using an end-capped non-polar C18 stationary reversed-phase column. In the present study, the correlations between the logarithm of the capacity factor k and log P/Clog P values calculated in various ways as well as the relationships between the lipophilicity and the chemical structure of the studied compounds are discussed.