Zinc oxide nanoparticles:A highly efficient and readily recyclable catalyst for the synthesis of xanthenes

A novel and efficient route for the synthesis of 1,8-dioxooctahydroxanthenes and 14-aryl-14H-dibenzo[a,j]xanthenes is described through one-pot multi-component reaction of dimedone and 2-naphthol with various aryl aldehydes using ZnO nanoparticles under solvent-free conditions.This method provides a novel and improved pathway for the synthesis of xanthenes in the terms of excellent yields,short reaction times,reusability and low catalyst loading.     

Design, synthesis and antiviral potential of 14-aryl/heteroaryl-14H-dibenzo[a,j]xanthenes using an efficient polymer-supported catalyst

Polyethyleneglycol bound sulfonic acid (PEG-OSO?H), a chlorosulphonic acid-modified polyethylene glycol was successfully used as an efficient and eco-friendly polymeric catalyst in the synthesis of 14-aryl/heteroaryl-14H-dibenzo[a,j]xanthenes obtained from the reaction of 2-naphthol and carbonyl compounds under solvent-free conditions with short reaction times and excellent yields. The biological properties of these synthesized title compounds revealed that compounds 3b, 3c, 3f and 3i showed highly significant anti-viral activity against tobacco mosaic virus.     

Zirconia prepared from UIO-66 as a support of Ru catalyst for ammonia synthesis

The development of effective Ru catalyst for ammonia synthesis is of important practical value and scientific significance because of the wide application of ammonia as a fertilizer and its promising applications in the renewable energy. Generally, ZrO₂ was regarded as an inferior support for Ru catalyst used in ammonia synthesis. Here we prepare ZrO₂ with monoclinic phase and carbon species from ZrCl₄ following the preparation route of UiO-66 as well as ammonia treatment. Owing to the presence of a larger amount of hydrogen adsorption as well as the easier desorption of hydrogen species, the ill effect of hydrogen species on the nitrogen adsorption-desorption and ammonia synthesis can be effectively alleviated. The resulting ZrO₂-supported Ru catalyst showed 4 times higher ammonia synthesis activity than the conventional Ru/ZrO₂ obtained from zirconium nitrate.     

Ammonia-treated activated carbon as support of Ru-Ba catalyst for ammonia synthesis

Ammonia-treated activated carbon has been studied as a support of Ru-Ba catalyst for ammonia synthesis. It is shown that the introduction of nitrogen leads to a decrease of ammonia synthesis activity for the catalysts with a low Ba/Ru molar ratio, while no significant changes are obtained for the catalysts with a high Ba/Ru molar ratio, confirming that electronegative impurities suppress the activity in ammonia synthesis and consume part of the promoters. This revised version was published online in June 2006 with corrections to the Cover Date.     

Oxalic acid as a catalyst for efficient synthesis of bis-（indolyl）methanes,and 14-aryl- 14H-dibenzo[a,j]xanthenes in water

A simple, efficient, and environment benign route was developed for the preparation of bis-（indolyl）methanes and 14-aryl-14H- dibenzo[aj]xanthenes from condensation of various aromatic aldehydes or ketones with indole, and 2-naphthol, respectively, using oxalic acid catalyst in aqueous medium. Use of cheap and easily available catalyst, better yields and simple reaction protocol are the advantages of the present method.     

Cyclodextrin host as a supramolecular catalyst in nonpolar solvents: stereoselective synthesis of (E)-3-alkylideneoxindoles

Heptakis(6-O-triisopropylsilyl)-β-cyclodextrin (TIPS-β-CD) effectively formed inclusion complexes with oxindole and its derivatives as guests in nonpolar solvents. Their inclusion complex formation was remarkably affected by the position and size of substituents on the oxindole ring of the guest. The Knoevenagel condensation reaction of these oxindoles with cinnamaldehyde to give 3-alkylideneoxindoles was accelerated with enhanced E/Z selectivities in the presence of catalytic amounts of TIPS-β-CD.     

Lewis acid-catalysed one pot synthesis of substituted xanthenes

A direct synthesis of substituted xanthenes from salicylaldehydes and cyclohexenones or tetralones has been developed. The reaction is catalysed by Lewis acids like scandium triflate and furnishes substituted xanthenes in good to excellent yields using either microwave or thermal heating. Microwave heating results in significantly shortened reaction times of 30 min and generally higher yields.     

Oxalic acld as a catalyst for efficient synthesis of bis-(indolyl)methanes,and 14-aryl-14H-dibenzo[a,j]xanthenes in water

A simple,efficient,and environment benign route was developed for the preparation of bis-(indolyl)methanes and 14-aryl-14H-dibenzo[a,j]xanthenes from condensation of various aromatic aldehydes or ketones with indole,and 2-naphthol,respectively,using oxalic acid catalyst in aqueous medium.Use of cheap and easily available catalyst,better yields and simple reaction protocol are the advantages of the present method.     

Chemoselective synthesis of xanthenes and tetraketones in a choline chloride-based deep eutectic solvent

A chemoselective synthesis of tetraketone and xanthene derivatives, by means of tandem Knoevenagel condensation and Michael addition in choline chloride-based deep eutectic solvents (DESs), is presented. The reaction of readily available aldehydes and active methylene compounds in malonic acid- and ZnCl₂-based DES gives various xanthenes derivatives with good to excellent yields under mild reaction conditions. On the other hand, tetraketones were synthesized in almost quantitative yields by simple condensation of an aldehyde and active methylene compounds in milder deep eutectic solvents of urea and SnCl₂. In addition, the reaction of other types of choline chloride-based DES leads to a mixture of tetraketone and xanthene.     

1,3-Dibromo 5,5-dimethylhydantoin (DBH):A novel and efficient catalyst for the synthesis of 14-aryl-14H-dibenzo[a,j] xanthenes under solvent-free conditions

An atom-efficient and environment-friendly approach for the synthesis of aryl-14H-dibenzo[a,j]xanthenes (3a–o) via the one-pot reaction of β-naphthol and aryl aldehydes (1) catalyzed by DBH has been developed. The present approach offers several advantages such as reduced reaction times, moderate temperature, higher yields, solvent free, eco-friendly reaction condition, easy purification and economic availability of the catalyst.     

Fe(HSO4)3: An efficient, heterogeneous and reusable catalyst for the synthesis of 14-aryl- or alkyi-14H-dibenzo[a.j]xanthenes

Fe(HSO4)3 has been used as an efficient and reeyclable catalyst for the one-pot synthesis of 14-aryl- or alkyl-14H-dibenzo[a,j]xanthene derivatives by the reaction of 2-naphtol and aldehydes. Different types of aromatic and aliphatic aldehydes are used in the reaction and in all cases the products were obtained in good to excellent yields.     

Design of a zeolite capsule catalyst by controlling the support size for the direct synthesis of isoparaffin

Three kinds of H-ZSM-5 zeolite capsule catalysts were prepared on Co/SiO₂ catalyst pellets of different sizes. Characterization of the catalysts indicated that a defect-free H-ZSM-5 membrane had been constructed successfully on the Co/SiO₂ surface. The smaller Co/SiO₂ pellets were favorable for zeolite capsule growth under the same synthesis conditions. Zeolite capsule catalysts, especially the catalysts with smaller pellet sizes, had a higher isoparaffin selectivity compared with conventional FTS Co/SiO₂ catalyst and mixed catalyst of Co/SiO₂ with H-ZSM-5 zeolite.     

Application of highly sulfonated single-walled carbon nanotubes: An efficient heterogeneous catalyst for the one-pot synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes under solvent-free conditions

Highly sulfonated single-walled carbon nanotube-catalyzed synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes in excellent yields and very short reaction times. Sulfonated single-walled carbon nanotubes are prepared using a chemical and simple process and it characterized by Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, Thermal gravimetric analysis (TGA) and acid-base titration. The sulfonated single-walled carbon nanotube was easily separated by simple filtration and was recycled eight consecutive times without any loss in its activity.     

A rapid synthesis of high surface area PdRu nanosponges:Composition-dependent electrocatalytic activity for formic acid oxidation

Here, Pd Ru nanoparticle networks(NPNs) with various compositions were synthesized through an inexpensive method in water as a green solvent, at different ratios of the H_2PdCl_4 and RuCl_3 precursors. This is a fast, room temperature and surfactant free strategy which is able to form high surface area metal nanosponges with a three-dimensional(3D) porous structure. The structure of as-prepared nanosponges was characterized using the techniques of field emission scanning electron microscopy(FESEM), energy dispersive spectroscopy(EDS) and cyclic voltammetry(CV). Then, the electrocatalytic activities of Pd Ru NPNs towards formic acid oxidation were examined by electrochemical measurements including CV,chronoamperometry, and electrochemical impedance spectroscopy(EIS). Based on studies, it was found that the current density of formic acid oxidation(FAO) is strongly dependent on the composition of Pd Ru NPNs. The best performance was realized for Pd_4Ru_1 NPNs compared to monometallic Pd counterpart and other bimetallic NPNs which might be ascribed to the role of Ru in the decrease of CO adsorption strength on the catalyst and consequently the priority of formic acid oxidation through the direct pathway. The Pd_4Ru_1 NPNs also showed the maximum current density and stability in chronoamperometric measurements. In addition, comparative studies were performed between as-prepared NPNs and CNTs-supported Pd nanoparticles(Pd NPs/CNTs). The present results demonstrated the unique structural advantages of NPNs compared to individual Pd NPs supported on the CNT which leads to the promising performance of NPNs as supportless catalysts for the oxidation of formic acid.     

Acrylamide-based magnetic nanosponges: a new smart nanocomposite material

Nanocomposite materials consisting of CoFe2O4 magnetic nanoparticles and a polyethylene glycol-acrylamide gel matrix have been synthesized. The structure of such materials was studied by means of small-angle scattering of X-rays and polarized neutrons, showing that the CoFe2O4 nanoparticles were successfully and homogeneously embedded in the gel structure. Magnetic, viscoelastic, and water retention properties of the nanocomposite gel confirm that the properties of both nanoparticles and gel are combined in the resulting nanomagnetic gel. Scanning electron microscopy highlights the nanocomposite nature of the material, showing the presence of a gel structure with different pore size distributions (pores with micron and nano-size distributions) that can be used as active sponge-like nanomagnetic container for water-based formulations as oil-in-water microemulsions.     

Sulfamic acid: a novel and efficient catalyst for the synthesis of aryl-14H-dibenzo[a.j]xanthenes under conventional heating and microwave irradiation

A simple and convenient procedure for the synthesis of aryl-14H-dibenzo[a.j]xanthenes is described through a one-pot condensation of β-naphthol with aryl aldehydes in the presence of sulfamic acid as the catalyst in a solvent-free media using both conventional heating and microwave irradiation.     

l-proline as an efficient asymmetric induction catalyst in the synthesis of chromeno[2,3-d]pyrimidine-triones,xanthenes in water

The multi-component reactions involving aromatic aldehydes, dimethylcyclohexane-1, 3-dione/cyclohexane-1, 3-dione and barbituric acids were carried out in presence of the organo catalyst l-proline in aqueous medium at ambient temperature. The reactions afforded chromeno[2,3-d]pyrimidinones in excellent yields and with high enantioselectivities. The above reactions exhibited the efficient asymmetric induction property of the organo catalyst l-proline as reported earlier. In the absence of barbituric acid the method proved equally efficient when aromatic aldehydes readily condensed with 2 mol of cyclohexane-1, 3-dione in presence of l-proline to give Xanthenes derivatives in good yields. The protocol reported here is benign to the environment as water is used as the solvent and purification does not involve any chromatographic procedures. Selected compounds were further studied using DFT calculations in order to establish a clear picture about the geometric parameters and the electronic absorption spectra of the compounds.     

Binolam-AlCl: a two-centre catalyst for the synthesis of enantioenriched cyanohydrin O-phosphates

The enantioselective synthesis of cyanohydrin O‐phosphates by using in situ generated bifunctional catalysts (R)‐ or (S)‐3,3′‐bis(diethylaminomethyl)‐1,1′‐binaphthol–aluminium chloride (binolam–AlCl) is reported. The reaction, which can be described as an overall cyano‐O‐phosphorylation of aldehydes, has a wide scope and applicability. Evidence is also provided, including ab initio and DFT calculations, in support of supported by the Lewis acid/Brønsted base (LABB) dual role of the catalyst in inducing first the key enantioselective hydrocyanation, which is then followed by O‐phosphorylation. A brief screening of the synthetic usefulness of the resulting cyanohydrin O‐phosphates unveiles some interesting applications. Among them, chemoselective hydrolysis, reduction and palladium‐catalysed nucleophilic allyl substitution, thereby leading to enantiomerically enriched α‐O‐phosphorylated α‐hydroxy esters, β‐amino alcohols and γ‐cyanoallyl alcohols, respectively. Naturally occurring (?)‐tembamide and (?)‐aegeline are synthesised accordingly.