Magnetic nanoparticle supported amine: An efficient and environmental benign catalyst for versatile Knoevenagel condensation under ultrasound irradiation

Amine functionalized silica coated Fe₃O₄ nanoparticles (SiO₂@MNP-A) were successfully prepared as a novel heterogeneous amine. The catalyst was characterized by XRD, FT-IR, TEM, magnetic measurement, elemental analysis and was found to be a magnetically separable and highly active catalyst for ambient Knoevenagel condensation of aromatic aldehydes and α-aromatic (heteroaromatic or polyaromatic)-substituted methylene compounds in water under ultrasonic irradiation to afford the corresponding products in good to excellent yields. Very interestingly, SiO₂@MNP-A successfully catalyze the reaction of the non-cyano substituted compound with benzaldehyde to achieve a key intermediate for the preparation of Atorvastatin calcium in green and atom-economic manner. In addition, the catalyst SiO₂@MNP-A can be reused for 8 times without any obvious loss of its activity. The role of ultrasonication in the Knoevenagel condensation was also discussed with the assistance of UV–vis spectrometry.     

Preparation, characterization and catalyst application of ternary interpenetrating networks of poly 4-methyl vinyl pyridinium hydroxide-SiO2-Al2O3

In this work, Al₂O₃ was mixed with SiO₂ and poly 4-vinylpyridine by the sol-gel method in order to make a composite which is used as a heterogeneous basic catalyst for Knoevenagel condensation reaction. The physical and chemical properties of the composite catalyst were investigated by XRD, FT-IR, TG, BET and SEM techniques. The catalytic performance of each material was determined for the Knoevenagel condensation reaction between carbonyl compound and malononitrile. The reactions were performed in solvent-free conditions and the product was obtained in high yield and purity after a simple work-up. The effects of the amount of catalyst, amount of monomer for the synthesis of composite and recyclability of the heterogeneous composite were investigated. The composite catalyst used for this synthetically useful transformation showed considerable level of reusability besides very good activity.     

Titanium isopropoxide/pyridine mediated Knoevenagel reactions

We report a Ti(OiPr)₄/pyridine-mediated Knoevenagel reaction between aromatic ketones and cyanoacetamides to provide Knoevenagel olefin products in good to excellent yields. Almost in all cases studied, a single geometrical isomer was formed and isolated under the Ti(OiPr)₄/pyridine condensation conditions. This methodology was also demonstrated to be highly effective between some other Knoevenagel active methylene compounds and aromatic ketones.     

聚乙烯基胺包裹Fe3O4@SiO2磁性微球用于Knoevenagel缩合（英文）简

Polyvinyl amine coated Fe₃O₄@SiO₂ composite microspheres with a core-shell structure were prepared and employed as a magnetic catalyst for Knoevenagel condensation under mild conditions. The catalyst can be readily recovered using a magnet and reused several times without loss in activity or selectivity. The performance of the magnetic base catalyst was compared with that of polyvinyl amine functionalized mesoporous SBA-15, which showed that the magnetic nanoparticles gave improved reaction rate and yield.     

Fe3O4–cysteamine hydrochloride magnetic nanoparticles: New,efficient and recoverable nanocatalyst for Knoevenagel condensation reaction

Fe₃O₄ magnetic nanoparticles (MNPs) were obtained using a reduction–precipitation method. These MNPs were modified with cysteamine hydrochloride. This catalyst was characterized using a number of physicochemical measurements. The Fe₃O₄–cysteamine MNPs, as an efficient and heterogeneous catalyst, were successfully used for Knoevenagel condensation under mild conditions. The activity of this nanomagnetic catalyst in the Knoevenagel condensation of aromatic aldehydes and malononitrile is described. Easy preparation of the catalyst, easy work‐up procedure, excellent yields and short reaction times are some of the advantages.     

离子液体功能化二氧化硅催化Knoevenagel反应

在100 ℃, 无外加溶剂条件下, 离子液体功能化二氧化硅催化一系列芳醛和活泼亚甲基化合物进行Knoevenagel 缩合反应, 以高产率生成相应产物. 当反应底物为水杨醛与氰基乙酸乙酯的时候, 产物为3-乙氧基羰基香豆素, 这是水杨醛和氰基乙酸乙酯缩合关环, 再发生氰基醇解的产物. 采用离子液体功能化二氧化硅作为反应催化剂, 反应后催化剂可回收再利用.     

A Straightforward Method for the Synthesis of Functionalized Trisubstituted Alkenes through Na2S/Al2O3 Catalyzed Knoevenagel Condensation

Na₂S/Al₂O₃ catalyzed the Knoevenagel condensation between an aldehyde and an active methylene compound to yield various trisubstituted alkenes.     

Cellulose stabilized Fe3O4 and carboxylate-imidazole and Co-based MOF growth as an exceptional catalyst for the Knoevenagel reaction

In this study, Fe₃O₄ nanoparticles were functionalized with cellulose, and then hybridized with cobalt (II)-based metal-organic framework (Co-MOF) containing carboxylate and imidazole functionalities. FTIR, XRD, FE-SEM, TEM, BET, EDX, VSM and STA analyses were used to characterize the synthesized samples. The resultant Fe₃O₄/cellulose/Co-MOF nanocomposite was applied efficiently as a powerful and economic heterogeneous catalyst in the condensation of a variety of different aromatic aldehydes with malononitrile under solvent-free conditions at room temperature for 10 min and offered the corresponding coupling products in high yields. The catalyst could be straightforwardly separated by a magnet from the reaction mixture and reused without a noteworthy drop in catalytic activity at least five times. The use of Fe₃O₄/cellulose/Co-MOF catalyst outcomes under mild reaction conditions in very short reaction time, outstanding catalytic activity, high recyclability and an easy work-up process for Knoevenagel condensation.     

对苯二甲酸镁作为钠离子电池的有机负极材料

报道了对苯二甲酸镁作为钠离子电池负极材料的研究. 以对苯二甲酸和氢氧化镁为原料,采用酸碱中和反应制备了含结晶水的对苯二甲酸镁（MgC₈H₄O₄·2H₂O）,该材料对钠离子电池表现出了较好的电化学活性、优异的倍率性能以及良好的循环稳定性. 在0.5C（1C=300 mA·g^-1）倍率下循环50 周以后,可逆容量由114mAh·g^-1降至95 mAh·g^-1,容量保持率高达83%;在2C的倍率下有高达90 mAh·g^-1的可逆比容量. 另外,在氮气气氛中,400 ℃进行后续热处理得到了不含结晶水的对苯二甲酸镁（MgC₈H₄O₄）,探讨了结晶水对其电化学性能的影响. 结果表明,MgC₈H₄O₄·2H₂O的比容量、倍率性能以及循环稳定性都明显优于不含结晶水的对苯二甲酸镁.     

Application of Microwave irradiation Techniques for the Knoevenagel Condensation

The reaction rate of Knoevenagel condensation can be dramatically enhanced by irradiating the reaction mixture containing an aldehyde, diethyl malonate, P₂O₅, piperidine, and chlorobenzene with a commercial microwave oven. Six Knoevenagel condensation products were synthesized within 5–15 min in good yields.     

Magnesium perchlorate as efficient Lewis acid for the Knoevenagel condensation between β-diketones and aldehydes

A new protocol for the Knoevenagel condensation between β-diketones and aliphatic and aromatic aldehydes promoted by Mg(ClO₄)₂ under mild conditions is reported.     

Surface Modification of a Magnetic SiO2 Support and Immobilization of a Nano-TiO2 Photocatalyst on It

This study presented an effective method to modify the surface chemical reactivity of a SiO₂/Fe₃O₄ support. The unmodified SiO₂/Fe₃O₄ support was prepared by the hydrolysis and condensation of tetraethoxysilane on the surface of hydrophilic Fe₃O₄ nanoparticles. These were then modified by a heat treatment in an ethanol/water solution under reflux. The resulting samples were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and transmission/scanning electron microscopy. The immobilization of a TiO₂ nanocatalyst on both unmodified and modified supports was performed to investigate the effects of the modification of the magnetic silica support on the loading of a TiO₂ nanocatalyst and the photocatalytic activity. The loading of TiO₂ and the photocatalytic activity were both improved.     

Selective Synthesis of 2‐Aryl‐1‐benzylated‐1H‐benzimidazoles

An efficient and simple procedure was developed for the green synthesis of various 2‐aryl‐1‐ben‐zylated‐1H‐benzimidazoles in high yields by condensation of o‐phenylenediamine with aldehydes with P₂O₅/SiO₂ as catalyst under solvent‐free and ambient conditions.     

A Practical Knoevenagel Condensation Catalyzed by PEG400 and Anhydrous K2CO3 Without Solvent

Abstract

Knoevenagel condensation of aromatic aldehydes with active methylene compounds under solvent‐free conditions to synthesize arylidene compounds in good to excellent yields using powdered anhydrous K₂CO₃ and PEG400 as catalysts has been described.     

Über den Einfluß von Kristallkeimen auf die Bildung von Silicaten der Zusammensetzung 3 CaO · 2 SiO2

On the Influence of Seed Crystals on the Formation of Calcium Silicates with the Composition 3 CaO · 2 SiO₂ The formation of the calcium silicates kilchoanite and rankinite of the composition 3 CaO · 2 SiO₂ is facilitated and enabled, respectively, in the presence of appropriate seed crystals. Kilchoanite (Ca₆[(SiO₄)(Si₃O₁₀)]) is formed from mixtures of CaO and SiO₂ in the autoclave at 200°C and from C? S? H (di, poly) under normal atmosphere at 700°C by seeding for example with kilchoanite, aluminium compounds, γ-Ca₂SiO₄. Rankinite (Ca₃Si₂O₇) can be synthesized under the same conditions, when rankinite itself is applied as seed crystal.     

Microwave-Assisted Efficient One-Pot Synthesis of Nitriles From Aldehydes in the Presence of P2O5/SiO2 in Solvent-Free Media

Abstract

A rapid and efficient procedure is developed for a one-pot synthesis of nitriles by condensation of aldehydes with hydroxylamine hydrochloride in the presence of P₂O₅/SiO₂ in solvent-free media under microwave irradiation.     

Neue cyclische Ester der Malonsäure und deren Kondensationsprodukte mit Aldehyden

The reaction of malonylchloride with ethylene glycol or dithioglycol at low temperatures and high dilution leads to cyclic condensation products of 2∶2 composition, of which the first one reacts with aldehydes to give alkenes (Knoevenagel condensation). On the other hand, malonyl chloride and pinacol react under the same conditions to give a linear oligomeric condensation product. The Knoevenagel condensation products are electrically neutral organic Lewis acids (pK′ _L -values: 8.3₅ and 7.8₅). Mass-spectra, NMR-, UV- and IR-spectra were employed for structural determinations.     

Organic‐Free,ZnO‐Assisted Synthesis of Zeolite FAU with Tunable SiO2/Al2O3 Molar Ratio

Zeolite FAU with tunable SiO₂/Al₂O₃ molar ratio has been successfully synthesized in the absence of organic structure‐directing agents (OSDA). Specifically, the addition of zinc species contributes to the feasible and effective adjustment of the framework SiO₂/Al₂O₃ molar ratio between about 4 and 6 depending on the amount of zinc species added in the batch composition. In contrast, a typical OSDA such as tetramethylammonium hydroxide (TMAOH) has a limited effect on the SiO₂/Al₂O₃ molar ratio of the zeolite. The role of zinc species is essential for the crystallization of zeolite FAU with a higher SiO₂/Al₂O₃ molar ratio under the particular synthesis conditions. It is speculated that zinc species may suppress the incorporation of aluminum into the aluminosilicate framework, which is due to the Coulombic repulsive interaction. A higher SiO₂/Al₂O₃ molar ratio is also found to be accompanied by a lower CO₂ adsorption heat for CO₂/CH₄ separation.     

A three component one-pot synthesis of N-amino-2-pyridone derivatives catalyzed by KF-Al2O3

Synthesis of 1,6-diamino-4-phenyl-3,5-dicyano-2-pyridone derivatives via a one-pot, three-component reaction of aryl aldehydes, malononitrile, and cyanoacetic hydrazide at room temperature using KF-Al₂O₃ as a recyclable catalyst have been developed. The reaction proceeds through the initial Knoevenagel condensation between aldehyde and malononitrile in the presence of KF-Al₂O₃ to form the benzylidene derivative which then undergoes Michael addition with cyanoacetic hydrazide followed by intramolecular cyclization of the resulting intermediate to produce the N-amino-2-pyridones in good to excellent yields. The structure of the synthesized compounds were characterized and established on the basis of their spectral data analysis and single-crystal XRD analysis.     

Thermal studies on sodium silicate hydrates. IV. Thermal stability of sodium silicate hydrates Na2[SiO2(OH)2]·nH2O(n = 4, 5, 7, 8). Phase relations and decomposition characteristics under open-system conditions

Thermoanalytic studies carried out on hydrate phases Na₂[SiO₂(OH)₂]·nH₂O (n = 4, 5, 7, 8) reveal two phase transitions at elevated temperatures under open-system and non-isothermal conditions

Congruent melting at temperatures T_mp is followed by condensation at temperatures T_c > 380 K with subsequent formation of solid Na₂[SiO₃]. Foamingof the melts upon condensation is observed through heating stage microscopy. In situ ²⁹Si NMR experiments proved oligomeric or endless chain-type anions, [Si_1+nO_2+3n(OH)₂]^(2+2n)?, to be formed in the melts under open-system conditions. From DTA double peak configurations at temperatures T_c the thermal decomposition of the melts is shown to occur in a two-step reaction, uniformly with all four hydrate phases.Isothermal studies below melting temperatures show distinct decomposition of crystalline Na₂[SiO₂(OH)₂]·8H₂O to crystalline Na₂[SiO₂(OH)₂]·4H₂O whereas all the other crystallinephases within this hydrate series dehydrate to amorphous waterglass-type materials under identical experimental conditions in long-term annealing experiments. This exceptional phase relation between the octa- and the tetrahydrate has also been proved by X-ray powder diffraction heating experiments.