CuI as reusable catalyst for the Biginelli reaction

An improved protocol for the Biginelli reaction using CuI as a reusable catalyst is described. The synthesis of 3,4-dihydropyrimidin-2(1H)-ones was achieved in acetonitrile, water and under solvent-free condition. After separation of product from the reaction mixture, the mother liquor (acetonitrile or water) containing the catalyst was reused two times without any loss of activity.     

Organometallic-like C-H bond activation and C-S bond formation on the disulfide bridge in the RuSSRu core complexes

C-S bond formations on the disulfide bridge in the dinuclear Ru(III) complexes have been found in the reaction with unsaturated organic molecules, such as alkenes and ketones. The reactions are initiated by the organometallic-like C-H bond activation. Through the mechanistic study of these novel reactions, the specific nature of the disulfide bridging ligand has been unveiled: (i) the double bond character of the sulfur-sulfur bond, which allows the Diels-Alder-type [4 + 2] cycloaddition reaction with butadiene to form a C(4)S(2) ring, (ii) the C-H bond activation on the S-S bond forming a C-S bond. All of the C-H activation reactions and the ensuing C-S bond formation reactions suggest that the disulfide ligand can act in a manner similar to the transition metal centers of the organometallic complexes.     

Raw halloysite as reusable heterogeneous catalyst for esterification of lauric acid

The methylic and ethylic esterifications of lauric acid were investigated using raw halloysite as a catalyst, in heterogeneous media. The reactions were conducted with different molar ratios (alcohol:lauric acid) and proportions of catalyst, at 160 °C for 2 h in a pressurized steel reactor. Halloysite produced lauric acid conversion of 95.02% and 87.11% for the methylic and ethylic esterifications, respectively. These results were better than those obtained from thermal conversion (75.61% and 59.86% for methanol and ethanol, respectively). After four consecutive reaction cycles, halloysite was recovered and could be reused after washing and drying. The results showed that halloysite is a promising inexpensive and reusable material for esterification reactions involving fatty acids.     

Polyaniline-supported acid as an efficient and reusable catalyst for a one-pot synthesis of β-acetamido ketones via a four-component condensation reaction

Polyaniline-supported acid salts such as polyaniline-hydrochloride, polyaniline-sulfate and polyaniline-nitrate were prepared by oxidation of aniline using ammonium persulfate as oxidizing agents. Polyaniline salts were used as catalyst for the preparation of β-acetamido ketones. Polyaniline-sulfate salt was found to be the best catalyst for the preparation of β-acetamido ketones. Present methodology offers several advantages, such as cheaper process, easy synthesis of stable catalyst, simple work-up procedure, and excellent activity with less amount of catalyst and in addition, the catalyst can be easily recovered after completion of the reaction and reusable without affecting its activity.     

Heterogeneous Fenton catalyst derived from hydroxide sludge as an efficient and reusable catalyst for anthraquinone dye degradation

Hydroxide sludge (HS) is the main by-product of drinking water production stations. In our work, we have promoted the valorization of these sludge, we convert it into activated carbon to serve as a support as a heterogeneous Fenton catalyst for reactive blue 19 (RB 19) degradation. The HS and Fe/HS-300 were characterized by means of SEM, EDX-ray, FTIR and XRD analysis. RB 19 and TOC removals were 92% and 41% respectively in optimal condition. More importantly, Fe/HS-300 exhibited an excellent stability and low Fe ion leaching (0.2–0.7mg/L), it was recycled 6 runs still maintaining the same efficiency.     

Palladium nanoparticles as reusable catalyst for the synthesis of N-aryl sulfonamides under mild reaction conditions

An efficient palladium nanoparticles-catalyzed N-arylation of sulfonamides and sulfonyl azides is described. This procedure serves as an active protocol for intermolecular C–N bond formation using Pd(OAc)₂ in PEG-400 under air. Aryl bromides and triflates react at 35°C, while aryl chlorides require heating to 50°C and give the desired products only in low yields. This reaction proceeds smoothly in acceptable yields using low catalyst loading.     

SO3H-functionalized ionic liquid as efficient,green and reusable acidic catalyst system for oligomerization of olefins

SO₃H-functionalized ionic liquids have been employed as an alternative reaction medium to conventional acid catalysts for oligomerization of various olefins, to produce branched olefin derivatives in high conversions and excellent selectivity. The ionic liquid plays a dual role as both catalyst and solvent, providing an efficient and reusable acidic catalyst system for the oligomerization of olefins.     

H6P2W18O62: An efficient and reusable catalyst for one-pot synthesis of β-acetamido ketone and esters

An efficient and improved procedure for the synthesis of β-acetamido carbonyl compounds is developed by a Wells–Dawson type Heteropolyacid catalyzed three-component coupling protocol.     

An efficient,reusable copper-oxide/carbon-nanotube catalyst for N-arylation of imidazole

Copper oxide nanoparticles (CuONPs) were successfully decorated on acid treated multi-wall carbon nanotubes (f-MWCNTs) using copper acetate precursor by a very simple “mix and heat” method, and was used as a heterogeneous nanocatalyst for the N-arylation of imidazole for the first time. The transmission electron microscopic (TEM) images of the prepared nanocatalyst (CuO/MWCNT) showed a good adhesion of CuONPs on anchoring sites of the MWCNTs. The factual loading of Cu in CuO/MWCNT was 7.64 wt% as confirmed by inductively coupled plasma-mass spectrometry (ICP-MS). The chemical state of Cu on MWCNTs was +2 as revealed by wide angle X-ray diffraction (WAXD), X-ray photoelectron spectroscopic (XPS) and temperature programmed reduction (TPR) techniques. Initially the reaction conditions were optimized and then the scope of the catalytic system was extended with different aryl halides. 0.98 mol% (5 mg) of the catalyst was sufficient for N-arylation of imidazole. A literature survey showed that this is the smallest amount of catalyst used for this reaction in research reported to date. The CuO/MWCNT is chemically as well as physically very stable, heterogeneous in nature and reusable. After the catalytic reaction, MWCNTs were successfully separated from the used CuO/MWCNT and characterized by Raman, TEM and WAXD.     

Polyaniline-sulfate salt as an efficient and reusable catalyst for the synthesis of 1,5-benzodiazepines and 2-phenyl benzimidazoles

Polyaniline-sulfate salt was used as an efficient catalyst for the preparation of benzodiazepines and 2-phenyl benzimidazoles in excellent yields. This method is applicable for the reaction of phenylenediamine with cyclic or acyclic ketones or aromatic aldehydes. The salient features of the present methodology are cheaper process, easy synthesis of stable catalyst, versatility and in addition, the catalyst can be easily recovered after completion of the reaction and reusable without affecting its activity.     

Mannich reaction in water using acidic ionic liquid as recoverable and reusable catalyst

The task-specific room-temperature ionic liquid (TSIL) N, N, N-trimethyl-N-butanesulfonic acid ammonium hydrogen sulfate [TMBSA]HSO₄ was synthesized as a cheap and recyclable catalyst for one-pot three-component Mannich reaction in water. Sixteen β-amino carbonyl compounds were obtained in good yields under the mild conditions. The products could simply be separated from the catalyst/water, and the catalyst could be reused at least 7 times without noticeably decreasing the catalytic activity.      

Reduced graphene oxide supported chiral Ni particles as magnetically reusable and enantioselective catalyst for asymmetric hydrogenation

A reduced graphene oxide (rGO) supported chiral-modified Ni catalyst was synthesized, characterized and employed for asymmetric hydrogenation. The prepared hybrid catalyst could produce each enantiomer with d- or l-tartaric acid as chiral modifier and exhibited a high TOF (20160 h⁻¹) and enantioselectivity (enantiomeric excess, 98.5%) for asymmetric hydrogenation of methyl acetoacetate. The high catalytic activity and enantioselectivity were mainly attributed to the unique properties of the support rGO, as it had a large specific surface area to sustain and stabilize Ni particles and its high charge carrier mobility could enable the readily transfer of electrons in the reaction process. Besides, the catalyst could also gain an enhanced reactant sorption with the support of rGO, thus achieved a greatly catalysis enhancement. The ferromagnetism of Ni made the catalyst easier for separation and reuse. The catalytic and recycling performance of the prepared chiral Ni catalyst demonstrated that rGO was indeed a promising support to improve activity, enantioselectivity and durability of catalysts, and the prepared catalysts were promising reusable heterogeneous catalysts for asymmetric hydrogenation.     

A readily prepared,highly reusable and active polymer-supported molybdenum carbonyl Schiff base complex as epoxidation catalyst

Polymer-bound Schiff base ligand 2 was prepared by oxidation of chloromethylated polystyrene to aldehydic polystyrene 1 and then reaction with ethylene diamine. The functionalized polystyrene 2 was used to immobilize Mo(CO)₆ and polymer-bound molybdenum carbonyl Schiff base catalyst 3 was produced. This supported catalyst shows high activity in epoxidation of various alkenes in the presence of tert-butylhydroperoxide (TBHP). The supported molybdenum catalyst can be recovered and reused for eight times without loss in its activity.     

Polyethylene glycol as an efficient and reusable solvent medium for the synthesis of thiohydantoins using K2CO3 as catalyst

Polyethylene glycol was found to be an inexpensive, non-toxic, recyclable and an effective medium for the synthesis of thiohydantoin derivatives in the presence of K₂CO₃ as the catalyst. The procedure is operationally simple and environmentally benign.     

Efficient trimethylsilylation of alcohols and phenols in the presence of ZrCl4 as a reusable catalyst

ZrCl₄ can be used as an efficient and reusable catalyst for the conversion of alcohols and phenols to their corresponding trimethylsilyl ethers with hexamethyldisilazane (HMDS). All reactions were performed under mild and completely heterogeneous reaction conditions in good to high yields.     

Synthesis of 1-benzoylpyrene using silica-supported phosphotungstic heteropoly acid as an efficient and reusable catalyst

A novel one-pot catalytic synthesis of 1-benzoylpyrene through acylation of pyrene with benzoic anhydride catalyzed by several heteropoly acids (HPAs) was investigated. Pure 1-benzoylpyrene was obtained and its structure was identified by GC/MS, FT-IR and ¹H NMR spectra. Silica-supported phosphotungstic heteropoly acid (PW/SiO₂) was found to be the most active catalyst in the acylation. The yield and the selectivity of 1-benzoylpyrene were up to 62.5% and 100%, respectively. The effects of experimental parameters on the catalytic acylation reaction, and the possibility of reusability of PW/SiO₂ catalyst were studied. PW/SiO₂ catalyst is easily separable from the reaction mixture and reusable without loss of its activity.     

Studies on the functionalization of MWNTs and their application as a recyclable catalyst for CC bond coupling reactions

Functionalization of multi-walled carbon nanotubes (MWNTs) was studied using various anchoring methods. Among them, nitrene chemistry was employed as the method of choice to preserve desirable physical properties of MWNTs. Using this method, synthesis of carboxyl-functionalized carbon nanotubes (CNTs) was achieved, and then transition metals were incorporated on the linker-MWNT via reductive methods using hydrazine monohydrate. Among various reducing reagents, the use of hydrazine hydrate allowed us to load palladium uniformly. After immobilization of palladium on CNT, its role as a catalyst for CC bond coupling reaction (Suzuki reaction) was examined. The catalysts could be retrieved upon completion of the reaction by filtration and drying; the recycled catalysts could then be used in further reactions up to seven times before any loss in catalytic activity was observed. Further studies revealed that the Pd leached out of the MWNT may be responsible for the reactivity.