The role of pyruvic acid as starting material in some organic reactions in the presence of SBA-Pr-SO<Subscript>3</Subscript>H nanocatalyst

Pyruvic acid contains three different reactive positions: –COOH, ketone carbonyl and methyl groups. Correspondingly, pyruvic acid was applied as starting material in the modified Niementowski reaction and Aldol condensation using SBA-Pr-SO₃H as an efficient nanocatalyst. Aldol condensation of pyruvic acid and oxindole provided a new oxindol-based carboxylic acid which was subsequently used in the Ugi four-component reaction. Moreover, through the modified Niementowski reaction of pyruvic acid, new derivatives of quiazoline were produced in the presence of SBA-Pr-SO₃H. The obtained products are important due to their potentially biological active skeletons.     

A simple and clean method for multicomponent synthesis of spiro [indole-tetrahydropyrano(2,3-d)pyrimidine] derivatives using SBA-Pr-SO3H as catalyst under solvent-free conditions

Sulfonic acid functionalized SBA-15 (SBA-Pr-SO₃H) as a new nanoporous solid acid catalyst was applied in the green one-pot synthesis of spiro[indole-tetrahydropyrano(2,3-d)pyrimidine] derivatives via three-component reaction of isatins, malononitrile or cyanoacetic esters and barbituric acids under solvent-free conditions. SBA-Pr-SO₃H was proved to be an efficient heterogeneous nanoporous solid acid catalyst with a pore size of 6 nm, which could be easily handled and removed from the reaction mixture by simple filtration and can be recovered and reused several times without any loss of activity. The advantages of this methodology are high product yields, being environmentally benign, short reaction times, and easy handling.     

Application of SBA-Pr-SO<Subscript>3</Subscript>H in the synthesis of 2,3-dihydroquinazoline-4(1<Emphasis Type="Italic">H</Emphasis>)-ones: characterization,UV–Vis investigations and DFT studies

An efficient one-pot synthesis of 2,3-dihydroquinazoline-4(1H)-one derivatives 4a–l is described using SBA-Pr-SO₃H as a heterogeneous acid catalyst. The present methodology resulted in various derivatives of 2,3-dihydroquinazoline-4(1H)-one in good yield via a three-component reaction of isatoic anhydride, aldehydes and ammonium acetate. SBA-Pr-SO₃H played a significant role as an efficient mesoporous catalyst due to its pore size of 6 nm. Additionally, UV–Vis spectrum of the products was studied in order to investigate their application as UV absorbers.     

Synthesis of benzimidazoles/benzothiazoles by using recyclable,magnetically separable nano-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> in aqueous medium

An efficient, simple, ecofriendly and cost-effective method has been developed for the synthesis of benzimidazole/benzothiazole derivatives by a two-component reaction, involving 1,2-diamino benzene/2-amino thiophenol and substituted aromatic aldehydes using recyclable nano-Fe₂O₃ catalyst (10 mol%) in water afforded with excellent yields (75–85%). The most important feature of this protocol is short reaction times, high yields, aqueous reaction medium, efficient recycling and high stability of the catalyst.     

MCM‐41‐SO3H as a nanoreactor for the one‐pot,solvent‐free synthesis of 1,8‐dioxo‐9‐aryl decahydroacridines

One‐pot four‐component synthesis of 1,8‐dioxo‐9‐aryl decahydroacridines in solvent‐free condition was efficiently performed in the presence of MCM‐41‐SO₃H as a nanocatalyst and nanoreactor in good yields. The method provides several advantages such as low cost, operational and experimental simplicity, high yields, and short reaction times. J. Heterocyclic Chem., (2012).     

A concise synthesis of furo[3,2-c]coumarins catalyzed by nanocrystalline ZnZr<Subscript>4</Subscript>(PO<Subscript>4</Subscript>)<Subscript>6</Subscript> ceramics under microwave irradiation

A simple and concise method catalyzed by nanocrystalline ZnZr₄(PO₄)₆ ceramics has been reported for the synthesis of a series of trans-2-benzoyl-3-(aryl)-2H-furo[3,2-c]chromen-4(3H)-ones using a multicomponent reaction of 2,4′-dibromoacetophenone, benzaldehydes and 4-hydroxycoumarin under microwave irradiation. This method provides several advantages including easy workup, excellent yields, short reaction times, using of microwave as clean method, recoverability of the catalyst and little catalyst loading.     

Assembly of a Nanoreactor System with Confined Magnetite Core and Shell for Enhanced Fenton‐Like Catalysis

Conventional solid catalysts for heterogeneous Fenton‐like reactions in bulk solution usually suffer from aggregation and vulnerability, which greatly lower the catalytic efficiency and hamper their practical application. Herein, we demonstrate a promising yolk–shell nanostructure with both the core and the shell composed of magnetite (designated as yolk‐like Fe₃O₄@Fe₃O₄/C) as a nanoreactor capable of accommodating the Fenton‐like reaction into its void space. Benefiting from the mesoporous shell and perfect interior cavity of this composite, reactants can access and be abundantly confined within the microenvironment where Fe₃O₄ sites are dispersed on the entire cavity surfaces, thus leading to a higher catalytic efficiency compared with the conventional solid catalysts in bulk solution. The chosen model reaction of chlorophenols degradation in the presence of the as‐prepared materials as well as hydrogen peroxide (H₂O₂) confirms this assumption. Under the optimal reaction conditions, more than 97 % 4‐chlorophenol (4‐CP) can be degraded in the Fe₃O₄@Fe₃O₄/C nanoreactor, whereas only 28 % can be achieved by using bare Fe₃O₄ particles within 60 min. Furthermore, owing to the existence of the outermost carbon layer and high‐magnetization properties, the nanoreactor can be re‐used for several runs. The synthesized nanoreactor displays superior catalytic activity toward the Fenton‐like reaction compared with the bare solid catalysts, and thereby holds significant potential for practical application in environmental remediation.     

One-pot three-component process for the synthesis of substituted pyrano[2,3-<Emphasis Type="Italic">c</Emphasis>]pyrazoles catalyzed by nanostructured FSM-16-SO<Subscript>3</Subscript>H

A three-component process for the one-pot synthesis of 6-amino-4-aryl-5-cyano-3-methyl-1-phenyl-1,4-dihydropyrano[2,3-c]pyrazoles by the reaction of aldehydes, 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one, and malononitrile in the presence of FSM-16-SO₃H as an efficient mesoporous catalyst. The FSM-16-SO₃H was prepared and characterized by SEM, XRD, BET, and FT-IR techniques. The advantages of the presented method are high yields, short reaction times, easy purification of products, easy work-up, and reusability of the catalyst.     

The catalytic effect of Al-KIT-5 and KIT-5-SO<Subscript>3</Subscript>H on the conversion of fructose to 5-hydroxymethylfurfural

The aim of this work is to study the production of hydroxymethylfurfural (HMF) from fructose using heterogenous catalysts based on KIT-5. For this propose, Al-KIT-5 and KIT-5-SO₃H as the Lewis and Bronsted catalysts were prepared and were characterized using different techniques such as FT-IR, SEM, EDS, TEM, BET, TGA and elemental analysis. With the use of Al-KIT-5 as the catalyst, the appropriate reaction temperature and time were 135 °C and 60 min, respectively. Moreover, with the use of KIT-5-SO₃H as the catalyst, the proper reaction conditions were found to be 125 °C and 45 min, respectively. In addition, the corresponding amounts of catalyst weight were 40 and 50 mg for KIT-5-SO₃H and Al-KIT-5, respectively. Under these conditions, the conversion of fructose was 93.9 and 88.3%, respectively. These results indicated that, due to its Bronsted acid nature, the KIT-5-SO₃H catalyst showed better results when 40 mg catalyst was used at 125 °C for 45 min in DMSO as the solvent. Both catalysts could be recycled and reused several times.     

Synthesis and characterization of <Emphasis Type="Italic">N</Emphasis>-hydroxyphthalimide immobilized on SiO<Subscript>2</Subscript>-coated Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles as magnetic catalyst for oxidation of benzyl alcohols and hydrocarbons

In this study, N-hydroxyphthalimide (NHPI) was successfully attached on functionalized SiO₂-coated Fe₃O₄ nanoparticles through amid bond. The sustained nanomagnetite-immobilized NHPI as a new magnetically recoverable catalyst was characterized by FT-IR, XRD, TGA, VSM, TEM and SEM techniques. The prepared catalyst exhibited high selectivity for oxidation of various benzyl alcohols and hydrocarbons in the presence of hydrogen peroxide as oxidant. The catalyst can be readily separated from the reaction mixture using an external magnet and reused several times without significant loss of its catalytic activity.     

Sulfonic Acid–Functionalized Silica (SiO2-Pr-SO3H) as a Solid and a Heterogeneous Catalyst in Green Organic Synthesis: Recent Advances

The application of sulfonic acid–functionalized silica (SBA-Pr-SO₃H) as a catalyst in organic synthesis has become an efficient and green strategy for the selective construction of organic motifs. Therefore, the great efforts have been made by scientists to replace the conventional acid catalysts by sulfonic acid–functionalized silica used as solid, heterogeneous catalyst in various organic transformations. The sustainable advantage of sulfonic acid–functionalized silica is that it can be recovered and reused several times without loss of its efficiency. In this tutorial review, we attempt to give an overview about the use of sulfonic acid–functionalized silica as a catalyst in the synthesis of various organic compounds having industrial as well as pharmaceutical applications.     

Study on the oxygen exchange capacities of Ce<Subscript>2</Subscript>Sn<Subscript>2</Subscript>O<Subscript>7</Subscript> pyrochlore

Ce₂Sn₂O₇ pyrochlore was synthesized by a hydrothermal method. X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the composition and valence state of the sample. The oxygen exchange property of the Ce₂Sn₂O₇ phase was measured by an oxidation reaction in sealed air atmosphere and a followed reduction reaction in 5% H₂-95% N₂ atmosphere. Gas chromatography (GC) was used to analyze the oxygen change in the reaction. The results show that Ce₂Sn₂O₇ sample has excellent oxygen absorption capacity at 250°C as Ce³⁺ ions are oxidized to Ce⁴⁺ ions. The oxidized sample can be reduced by 5% H₂-95% N₂. The refreshed sample remains the capacity of oxygen absorption, while the oxygen exchange capacity degrades with the reduction times.     

Nano-cellulose-OSO<Subscript>3</Subscript>H as a new,green, and effective nano-catalyst for one-pot synthesis of pyrano [4,3-<Emphasis Type="Italic">b</Emphasis>] pyrans

A facile, green, and efficient method has been developed for the synthesis of biologically important pyrano [4,3-b] pyrans in the presence of nano-cellulose-OSO₃H as a new solid acid catalyst. The reaction involves the use of 4-hydroxy-6-methyl-2H-pyran-2-one, malononitrile, and aldehydes. A wide range of aldehydes is compatible in this reaction, producing excellent yields in short time. The morphology of nano-catalyst (nano-cellulose-OSO₃H) was observed using a scanning electron microscopy (SEM). The cellulose-OSO₃H surface was studied by the energy dispersive X-ray spectroscopy (EDX) method to find out the chemical composition. The decomposition steps and thermal stability of the catalyst were investigated by thermal analysis techniques (TGA/DTG). In addition, the vibrational spectrum analysis (FT-IR) and X-ray diffractogram (XRD) of the catalyst have been performed.     

Application of Sulfonic Acid Functionalized SBA‐15 as a New Nanoporous Acid Catalyst in the Green One‐Pot Synthesis of Spirooxindole‐4H‐pyrans

Sulfonic acid functionalized SBA‐15 (SBA‐Pr‐SO₃H) as a new nanoporous solid acid catalyst was applied in the green one‐pot synthesis of spirooxindole‐4H‐pyrans via condensation of isatins, malononitrile or methyl cyanoacetate or ethyl cyanoacetate, and 4‐hydroxycoumarin in water solvent. SBA‐Pr‐SO₃H was proved to be an efficient heterogeneous nanoporous solid acid catalyst with a pore size of 6 nm that could be easily handled and removed from the reaction mixture by simple filtration and can be recovered and reused for several times without any loss of activity. The significant merits of present methodology are its simplicity, short reaction time, good yields, and environmentally benign mild reaction condition as water was used as a green solvent.     

Charge separation by tetrahexahedron-SrTiO<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> heterojunction as an efficient photocatalyst

Charge separation plays a key role in the conversion of solar energy into chemical energy for use in the redox reaction and as well as in the photocatalytic activity. In this study, SrTiO₃ particles with different morphologies including irregular, tetrahexahedron, and cube were synthesized by an in situ solvothermal method. The photocatalytic activity of the synthesized nanoparticles was investigated in the photocatalytic decomposition of methylene blue under UV light irradiation. Tetrahexahedron SrTiO₃ particles exhibited high decomposition activity (70 %), which is about two times higher than those of the irregular and cubic SrTiO₃ particles. The high decomposition activity of tetrahexahedron SrTiO₃ particles could be attributed to the improvement of charge separation achieved on different crystal facets. To reach a good charge separation, tetrahexahedron SrTiO₃/TiO₂ coupled nanoparticles were fabricated by impregnation method. Results showed that coupling tetrahexahedron SrTiO₃ with TiO₂ could produce efficient charge separation between tetrahexahedron SrTiO₃ and TiO₂ due to their matched band edges. In order to achieve better charge separation, the tetrahexahedron SrTiO₃/90 %TiO₂ sample was calcined at different temperatures in the 450–750 °C range. Tetrahexahedron SrTiO₃/90 %TiO₂ coupled nanoparticles calcined at 650 °C show high photocatalytic activity compared with other samples. The prepared samples were characterized by using various techniques such as X-ray diffraction, scanning electron microscopy, photoluminescence emission spectra, and UV–Vis diffuse reflectance spectroscopy.     

Selective Acetylation of Alcohols and Amines with Ethyl Acetate in the Presence of H<Subscript>6</Subscript>[PMo<Subscript>9</Subscript>V<Subscript>3</Subscript>O<Subscript>40</Subscript>] as the Catalyst

Summary. Acetylation of various alcohols and benzyl amine was tested in the presence of H₆[PMo₉V₃O₄₀], a mixed addenda heteropolyacid, in ethyl acetate under reflux condition. Phenols and anilines are not affected under the reaction conditions. Selective transestrification of alcohols can be achieved in the presence of phenol and aniline derivatives using this method.     

H<Subscript>3</Subscript>PMo<Subscript>12</Subscript>O<Subscript>40</Subscript> immobilized chitosan/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> as a novel efficient,green and recyclable nanocatalyst in the synthesis of pyrano-pyrazole derivatives

A novel nanomagnetic composite heteropolyacid immobilized chitosan/Fe₃O₄ was prepared via a facile one-pot synthetic approach. This magnetically recoverable nanocatalyst, H₃PMo₁₂O₄₀/chitosan/Fe₃O₄ (PMo/chit/Fe₃O₄), was fully characterized by XRD, FTIR, SEM and EDX analysis methods. A rapid, efficient and the chemoselective synthesis of different pyrano-pyrazole derivatives was achieved in excellent yields via a one-pot four-component reaction in the presence of catalytic amount of PMo/Chit/Fe₃O₄.     

No-Glycerol rapid heterogeneous biodiesel production on K<Subscript>2</Subscript>CO<Subscript>3</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst by coupling process

Biodiesel containing almost no glycerol has been produced by coupling reaction carried out over K₂CO₃ supported by calcium oxide as solid base catalysts. The solid base catalysts synthesized by wet impregnation exhibit an exceedingly high activity in biodiesel production. It was found that the reaction time required for the highest yield of biodiesel, 99.2%, can be shortened to 30 min over K₂CO₃/Al₂O₃ under the optimum reaction conditions: 8: 1: 1 molar ratio of methanol/DMC/oil, 30 wt % K₂CO₃/Al₂O₃ catalyst, and 65°C reaction temperature. Solid basic catalysts examined in the study were characterized by BET surface area, XRD, CO₂-TPD, and SEM techniques. The strong interaction between K₂CO₃ and the support yields a new basic active site, which can be probably responsible for the high activity of K₂CO₃/Al₂O₃.     

Hydrolysis of cellulose by the heteropoly acid H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>

The potential of heteropoly acid H₃PW₁₂O₄₀ to catalyze the hydrolysis of cellulose to glucose under hydrothermal conditions was explored. This technology could contribute to sustainable societies in the future by using cellulose biomass. A study to optimize the reaction conditions, such as the amount of catalyst, reaction time, temperature, and the amount of cellulose used, was performed. A remarkably high yield of glucose (50.5%) and selectivity higher than 90% at 453 K for 2 h with a mass ratio of cellulose to H₃PW₁₂O₄₀ of 0.42 were achieved. This was attributed to the high hydrothermal stability and the excellent catalytic properties, such as the strong Brønsted acid sites. This homogeneous catalyst can be recycled for reuse by extraction with diethyl ether. The results illustrate that H₃PW₁₂O₄₀ is an environmentally benign acid catalyst for the hydrolysis of cellulose.     

MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/cellulose/SO<Subscript>3</Subscript>H nanocomposite: a new biopolymer-based nanocatalyst for one-pot multicomponent syntheses of polysubstituted tetrahydropyridines and dihydropyrimidinones

A new biopolymer cellulose-based magnetic heterogeneous catalyst, MgFe₂O₄/cellulose/SO₃H nanocomposite, was prepared. Fourier-transform infrared spectra, X-ray diffraction, energy-dispersive X-ray, field-emission scanning electron microscopy, thermal analysis (TG, DTG and DSC), dynamic light scattering and vibrating sample magnetometer measurements have been used to characterize the catalyst. Then, it was applied efficiently as an inexpensive and green catalyst in two multicomponent syntheses of polysubstituted tetrahydropyridines and dihydropyrimidinones under solvent-free conditions. The nanocatalyst can be recovered and reused several times without significant loss of catalytic activity.