Synthesis of 2-aryl-2,3-dihydroquinazolin-4(1<Emphasis Type="Italic">H</Emphasis>)-ones using boric acid-functionalized MCM-41 as a novel heterogeneous catalyst under solvent-free condition

Ordered mesoporous silica material MCM-41 with covalently anchored boric acid groups located inside the mesochannels has been utilized as an acid catalyst for the ‘green’ synthesis of 2-aryl-2,3-dihydroquinazolin-4(1H)-one derivatives under solvent-free condition. This novel synthetic method offers advantages, such as excellent yields, simple reaction procedure, short reaction times and mild reaction conditions.     

Convenient and Efficient One-Pot Method for the Synthesis of 2-Amino-tetrahydro-4H-chromenes and 2-Amino-4H-benzo[h]-chromenes Using Catalytic Amount of Amino-Functionalized MCM-41 in Aqueous Media

A convenient and efficient one-pot method for the synthesis of 2-amino-tetrahydro-4H-chromene and 2-amino-4H-benzo[h]-chromene derivatives has been developed using a catalytic amount of amino-functionalized MCM-41 in aqueous medium. This efficient technique has the advantages of giving 4H-tetrahydro-chromene and 4H-benzo[h]chromene building blocks using a reusable catalyst in good to excellent yields, to be completed in short reaction times with a simple product isolation procedure.     

Tethering of nickel(II) Schiff-base complex onto mesoporous silica: An efficient heterogeneous catalyst for epoxidation of olefins

A new hybrid catalyst has been prepared by tethering a nickel(II) Schiff-base complex via post-synthesis modification of mesoporous silica, MCM-41. The Schiff-base has been derived from salicylaldehyde and 3-aminopropyltriethoxysilane (3-APTES) which is chemically anchored on MCM-41 via silicon alkoxide route. The anchored Schiff-bases imposed a stable planar coordination geometry around the central nickel ions. The catalyst has been characterized by elemental analysis, FT-IR, UV-Vis, small angle X-ray diffraction (SAX) and transmission electron microscopy (TEM) studies. The SAX and TEM measurement showed the mesoporosity of the catalyst. The activity of the catalyst has been assessed in the epoxidation of olefins using tert-butyl-hydroperoxide (tert-BuOOH) as oxidant in heterogeneous condition. Immobilized nickel catalyst was found to be catalytically more active and selective compared to the similar type of nickel(II) complex as well as Ni(NO₃)₂·6H₂O in homogeneous media. The catalyst can be recycled and reused several times without significant loss of activity.     

Light olefins and light oil production from catalytic pyrolysis of waste tire

This paper investigates the catalytic activity of MCM-41 synthesized via silatrane route and Ru/MCM-41 in waste tire pyrolysis. The experimental results showed that the presence of catalysts strongly influenced the yield and nature of products. Namely, the gas yield increased at the expense of liquid yield. In addition, a considerable high yield of light olefins, 4 times higher than non-catalytic pyrolysis, can be achieved for Ru/MCM-41 catalyst. Furthermore, the uses of catalysts produced much lighter oil and there was a drastic increase in the concentration of single ring aromatics in accordance to a reduction in polycyclic aromatic compounds in the derived oils. Ru/MCM-41 produced the lightest oil and the oil has the highest concentration of mono-aromatics. The high activity of catalysts, particularly Ru/MCM-41 was discussed in relation with the catalyst characterization results obtained from various techniques including TPD-NH₃, H₂-chemisorption, XRD, N₂-adsorption/desorption analysis, and TPO.     

MCM-41固载胺钯配合物的制备及对Heck反应催化性能的研究

以MCM-41分子筛作为固载材料, 经氨基功能化后与各种钯化合物形成一系列MCM-41载钯配合物, 采用XRD, XPS等技术对其结构及表面性能进行了表征, 研究了催化剂的制备条件等因素对催化Heck芳基化反应性能的影响; 以共轭烯烃和各种芳基碘的Heck芳基化反应考察了MCM～NH₂•Pd(0, II)配合物的催化性能. 结果表明, MCM-41的结构没有被破坏, MCM～NH₂载钯配合物具有较高的催化活性和立体选择性, 在较低的温度(70～90 ℃)下, 可高产率地生成一系列取代的反式产物.     

Application of RuO<Subscript>2</Subscript> Nanoparticles as Catalyst in Preparation of Indolo[3,2-a]Carbazoles

RuO₂ nanoparticles were readily prepared from RuCl₃·3H₂O via the formation of Ru-hydroxide precursor, followed by calcination at 550 °C. Under similar conditions, uniform dispersion of spherical RuO₂ nanoparticles over the surface of MCM-41 was also obtained. The synthesized materials were characterized by transmission electron microscopy (TEM), infrared spectroscopy (FT-IR), X-ray diffraction (XRD), BET surface area measurements, and magnetic measurements (VSM). The obtained RuO₂ nanoparticles found application as catalyst in preparation of indolo[3,2-a]carbazoles from the reaction of indoles and benzils. Under mild reaction conditions, satisfactory yields of the desired products were obtained. Stabilization of RuO₂ nanoparticles over the surface of MCM-41 (RuO₂–MCM41), however, had the advantage of easy recycling, although a slight decrease in efficiency after five successive runs was observed.     

Influences of Mesoporous Structure on the NO+H2+O2 Low Temperature Reaction over Pt/Si-MCM-41 Catalyst

It was found that Si-MCM-41 mesoporous molecular sieves as a support of noble metal Pt could be used for the selective catalytic reduction of NO by hydrogen (H₂-SCR) under lean-burn conditions. Pt/Si-MCM-41, together with Pt/Si-ZSM-5 and Pt/SiO₂, was characterized by X-ray diffraction analysis (XRD), nitrogen adsorption/desorption, hydrogen adsorption, and transmission electron microscopy (TEM). The results indicated that Pt/Si-MCM-41 had the best H₂-SCR activity in comparison with Pt/Si-ZSM-5 and Pt/SiO₂ catalysts and that the maximum conversion of NO was up to 60.1% at 100 °C and a gas hourly space velocity (GHSV) of 80000 h_-1 under lean-burn conditions. Characterization showed that the large surface area and pore volume of MCM-41 favored the dispersion of Pt. The maximum NO conversion of Pt/Si-MCM-41 catalyst decreased obviously to 15% at 120 °C when the pore structure of Si-MCM-41 support was destroyed. The reaction mechanism over Pt/Si-MCM-41 was investigated using in situ diffuse reflectance infrared spectroscopy (DRIFTS), which revealed that the main reaction intermediates should be nitrate species during NO reduction.     

Heteropolyacid (H3PW12O40) supported MCM-41: An efficient solid acid catalyst for the green synthesis of xanthenedione derivatives

HPWA/MCM-41 mesoporous molecular sieves of appropriate ratios were prepared by loading HPWA on siliceous MCM-41 by the wet impregnation method. The prepared HPWA/MCM-41 materials were characterized by X-ray diffraction analysis (XRD) and BET surface area and FT-IR measurements. The morphology of mesoporous materials was studied by TEM observation. The catalytic activity of the above materials was tested for the condensation of dimedone (active methylene carbonyl compound) and various aromatic aldehyes under liquid phase conditions at 90 °C. The products were confirmed by FT-IR, ¹H NMR and ¹³C NMR studies. HPWA supported MCM-41 catalysts catalyses efficiently the condensation of dimedone and aromatic aldehydes in ethanol and other solvents under liquid phase conditions to afford the corresponding xanthenedione derivatives. Activities of the catalysts follow the order: HPWA/MCM-41(20 wt.%) > HPWA/MCM-41(30 wt.%) > H₃PW₁₂O₄₀·nH₂O > HPWA/MCM-41(10 wt.%) > HPWA/SiO₂ (20 wt.%) > HM (12) > Hβ (8) > Al-MCM-41 (50). Various advantages associated with these protocols include simple workup procedure, short reaction times, high product yields and easy recovery and reusability of the catalyst.     

MCM-41-supported bidentate phosphine palladium(0) complex as an efficient catalyst for the heterogeneous Stille reaction

A Stille coupling reaction of organostannanes with organic halides has been developed in the presence of a catalytic amount of MCM-41-supported bidentate phosphine palladium(0) complex (0.5 mol %) in DMF/H₂O (9:1) under air atmosphere in high yields. This polymeric palladium catalyst exhibits higher activity than Pd(PPh₃)₄ and can be reused at least 10 times without any decrease in activity.     

A general synthetic method for the formation of arylaminotetrazoles using natural natrolite zeolite as a new and reusable heterogeneous catalyst

An efficient method for preparation of arylaminotetrazoles is reported using natrolite zeolite as a natural catalyst. Generally, isomer of 5-arylamino-1H-tetrazole can be obtained from arylcyanamides carrying electron-withdrawing substituent on aryl ring and as the electropositivity of substituent is increased, the product is shifted toward the isomer of 1-aryl-5-amino-1H-tetrazole. This method has the advantages of high yields, simple methodology, short reaction times and easy work-up. The catalyst can be recovered by simple filtration and reused in good yields.     

Carbonyl allylation of aldehydes and ketones with allylic chlorides catalyzed by immobilization of palladium in MCM-41

The heterogeneous carbonyl allylation of aldehydes and ketones with allylic chlorides was achieved in DMF using SnCl₂ as reducing agent at 25-40 °C in the presence of a 3-(2-aminoethylamino)propyl-functionalized MCM-41-immobilized palladium(II) complex [MCM-41-2N-Pd(II)], yielding a variety of homoallylic alcohols in good to high yields. This heterogeneous palladium catalyst exhibited higher activity than (N-propylethylenediamine)PdCl₂ and can be recovered and recycled by a simple filtration of the reaction solution and used for at least 5 consecutive trials without any decreases in activity.     

Efficient and suitable preparation of N-sulfonyl-1,2,3,4-tetrahydroisoquinolines and ring analogues using recyclable H6P2W18O62·24H2O/SiO2 catalyst

Silica gel-supported H₆P₂W₁₈O₆₂·24H₂O is an efficient and recyclable catalyst for the synthesis of biologically important molecules. Several substituted N-sulfonyl-1,2,3,4-tetrahydroisoquinolines and ring analogues can be prepared in very good yields and purity by direct reaction of N-aralkylsulfonamides and sym-trioxane by a Pictet-Spengler reaction in the presence of a catalytic amount of silica gel-supported H₆P₂W₁₈O₆₂·24H₂O. Reactions were performed in a low volume of toluene, at 70 °C and for a short time, typically 15 to 30 min. The title heterocyclic compounds were prepared in very good yields (60%–95%) using the described procedure results in a clean and useful alternative, which has the advantages of a greener methodology with operative simplicity, use of a reusable and non-corrosive solid catalyst, soft reaction conditions, low reaction times, and good yields.     

Synthesis of 2,3-dihydroquinazolin-4(1<Emphasis Type="Italic">H</Emphasis>)-ones,disulfides and sulfoxides catalyzed by a zinc complex immobilized onto functionalized mesoporous MCM-41 as a mild and efficient catalyst

Zinc complex with 2-amino-3-hydroxy-pyridine ligand was immobilized onto chloropropyl-modified mesoporous silica MCM-41 (CP-MCM-41) via post-grafting method. The prepared catalyst has been characterized by low-angle X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive spectrum, atomic adsorption spectroscopy and thermogravimetric analysis. The immobilized nano-structured material showed very good catalytic activity and excellent recycling efficiencies for the oxidation reaction of sulfides to sulfoxides and oxidative coupling of thiols to their corresponding disulfides in the presence of aqueous hydrogen peroxide as oxidant at room temperature and the synthesis of 2,3-dihydroquinazolin-4(1H)-one derivatives in water.     

Ferricyanide immobilized within organically modified MCM-41; application for electrocatalytic reduction of hydrogen peroxide

Carbon paste electrode modified with aminated Mobil Catalytic Material Number 41 (MCM-41) was prepared and used for immobilization of K₃[Fe(CN)₆] in acidic medium, and then electrochemical behavior of modified electrode containing ferricyanide was studied in detail, including pH-dependence and scan rate effect. Cyclic voltammetry studies showed that the electrode reaction is a surface-controlled process at the scan rate range from 5 to 60 mV s⁻¹. Also, the electrocatalytic behavior of modified electrode toward the reduction of H₂O₂ is reported and the effect of pH on catalytic peak current was discussed. According to experimental results, with increasing solution pH, the catalytic effect of this modified electrode is decreased. Catalytic reduction current of H₂O₂ increases linearly with its concentration. It has been demonstrated that ferricyanide immobilized on the aminated MCM-41 is a stable catalyst for the electrocatalytic reduction of H₂O₂.     

Highly efficient and convenient Strecker reaction of carbonyl compounds and amines with TMSCN catalyzed by MCM-41 anchored sulfonic acid as a recoverable catalyst

MCM-41 anchored sulfonic acid (MCM-41–SO₃H) was found to be a highly efficient and recoverable heterogeneous catalyst for the three-component Strecker reaction of aldehydes or ketones and diverse amines using trimethylsilyl cyanide (TMSCN) to afford the corresponding α-amino nitriles under mild conditions in high to quantitative yields. The simple experimental procedure along with easy recovery and reusability of the catalyst has led to development of a clean and environmentally friendly approach for the synthesis of α-amino nitriles.     

Environmentally benign and highly regioselective ring opening of epoxides accelerated by ultrasound irradiation

Regioselective ring opening of aliphatic and aromatic epoxides with nitrogen heterocycles such as indoles and imidazoles was accelerated using an ultrasonic technique as a green approach. An optimized procedure with the catalyst of choice, MCM-41, represents a real alternative to the conventional reaction protocols owing to the catalyst recyclability, simplicity, green conditions and time-saving aspects.     

Heterogenization of [Ti(η-C5HMe4)Cl3] on to MCM-41 and organomodified MCM-41 to form epoxidation catalyst

This paper describes the heterogenization of a tetramethylmonocyclopentadienyl titanium (IV) trichloride complex, [Ti(η⁵-C₅HMe₄)Cl₃] onto mesoporous MCM-41. Its immobilization has been performed via a straightforward grafting process of the organometallic precursor in the pores of an MCM-41 host material and by reaction with previously organomodified MCM-41 material with a hydroxyl triazine based compound. Applying all-silica MCM-41 hosts, stable and heterogeneous liquid-phase epoxidation catalysts are obtained. Powder X-ray diffraction and nitrogen adsorption-desorption analysis indicated that the structural integrity of the support has been preserved during the titanium complex immobilization. These materials have been also extensively characterized using diffuse reflectance UV-vis, ¹³C and ²⁸Si MAS NMR and FT-IR spectroscopy. With these techniques the strong adsorption of the intact catalytic complex within an all-silica MCM-41 host is demonstrated. These materials have been tested as catalyst for the epoxidation of aliphatic and aromatic alkenes with TBHP as oxidant exhibiting a significant selectivity toward the epoxide with negligible leaching of titanium species. The conversion values are moderated, being the olefin trend reactivity 1-octene > cyclohexene > styrene.     

Practical one-pot synthesis of 5-alkynyl-1,2,3-triazoles via heterogeneous copper(I)-catalyzed tandem three-component click/alkynylation reaction

An efficient and practical route to 5-alkynyl-1,2,3-triazoles has been developed via heterogeneous tandem CuAAC/alkynylation reaction of organic azides, alkynes and 1-bromoalkynes by using an L-proline-functionalized MCM-41-anchored copper(I) complex [L-Proline-MCM-41-CuCl] as catalyst under mild conditions. The reaction produces a wide variety of 5-alkynyl-1,2,3-triazoles in mostly good to excellent yields. The new immobilized copper(I) complex can be readily prepared from commercially available and inexpensive reagents and displays the same catalytic activity as CuCl. The L-Proline-MCM-41-CuCl catalyst is also easy to recover via a simple filtration process and can be reused at least seven times without apparent loss of activity.     

Gold-vanadium-niobium catalysts in environmental protection—adsorption and interaction of NO, C3H6 and O2—FT-IR study

FT-IR study of NO and C₃H₆ adsorption, co-adsorption and interaction in the presence of oxygen were performed in order to estimate the catalytic behaviour of Au and V-containing MCM-41 materials in NO-SCR with propene. MCM-41 were modified with gold, vanadium and niobium by their introduction during the synthesis (co-precipitation) carried out with the use of HCl or H₂SO₄ as pH adjustment agent. The texture/structure properties of the prepared samples were investigated by N₂ adsorption, XRD, XPS and TEM techniques. It has been found that the nature of acid used for the pH adjustment during the synthesis determines the gold particles size and dispersion and influences the interaction of NO+O₂+C₃H₆ with the catalyst surfaces. In both types of AuVMCM-41 catalysts, the SCR reaction route occurs via NO₂ formation. In the case of AuVMCM-41(HCl) and AuVNbMCM-41(HCl) nitrites are formed and stored, and upon heating NO₂ is released. These kinds of nitrites are not formed on AuVMCM-41(H₂SO₄) and AuVNbMCM-41(H₂SO₄). Instead of that NO₂ is chemisorbed on metallic gold, niobium and vanadium species and reacts with propene and/or oxygenates.     

Syntheses of polycarbonate and polyurethane precursors utilizing CO2 over highly efficient, solid as-synthesized MCM-41 catalyst

As-synthesized MCM-41 was used as a reusable, heterogeneous catalyst for the eco-friendly synthesis of cyclic carbonate precursors of polycarbonates via a cycloaddition reaction of CO₂ with epoxides. This catalyst is also efficient for the synthesis of alkyl and aryl carbamate precursors of polyurethanes via the reaction of amines, CO₂ and alkyl halides. Both these reactions were carried out under mild conditions and without using any solvent or co-catalyst. CO₂ is utilized as a raw material replacement for toxic phosgene in the conventional synthesis of these chemicals.