Solvent-free Knoevenagel Condensation Research Articles

Synthesis, characterization, and novel reactivity of nano CeO2 catalyst for solvent-free Knoevenagel condensation

We synthesized the nano CeO2 using the sol-gel method and characterized the material using different techniques, including XRD, FT-IR, BET surface area, SEM, and TEM analysis. We tested the catalytic functionalities of nano CeO2 catalyst for Knoevengel condensation of different substituted benzaldehydes with malononitrile, which offered exceptional 95 % conversion and yield. The results support that nano CeO2 material significantly boosted the yield of the desired product compared to the bulk material. The low-angle XRD profile showed that the regenerated nanomaterial fully retained the porous nature and cubic structure of ceria. FT-IR results reveal that the characteristic vibrational IR band is at 720 cm−1, which is attributed to Ce–O–Ce stretching. The BET surface area result indicates that nano-ceria possesses a higher surface area than bulk CeO2 material. The SEM analysis illustrates cube-like morphology and TEM data show the nanorod-like appearance of ceria. The nanocatalyst exhibited stable and sustainable activity during regeneration up to 5 cycles.

Hydrothermal synthesis, characterization of Co3Sb4O6F6 and carbon doped Co3Sb4O6F6 and their application towards photocatalytic dye degradation, adsorption, catalytic Knoevenagel condensation and bacterial disinfection

Single crystals of Co3Sb4O6F6 have been grown by employing hydrothermal techniques. Table sugar was utilized to prepare carbon-doped Co3Sb4O6F6. The objective was to employ Co(II)-based metal oxyfluoride comprising a stereochemically active lone pair element (Sb3+) and its carbon-doped analogues for the multifunctional applications. The impact of carbon doping on Co3Sb4O6F6 has been evaluated towards the changes in photocatalytic, catalytic, and adsorbent efficiency. The changes in carbon percentage affect the physical and chemical properties of the host material. A larger percentage of carbon doping turns the photocatalytic ability of the host material into an adsorbent for the removal of dye. The single crystal X-ray diffraction study reveals that Co3Sb4O6F6 crystallizes into cubic symmetry. However, powder X-ray diffraction study reveals the structural transformation in the carbon-doped Co3Sb4O6F6. It also reduces the band gap energy of the host material, and 4 wt% C@Co3Sb4O6F6 turns out to be an efficient photocatalyst. Large-scale carbon doping (15 wt%) appears to be an effective strategy to increase the surface charge and BET surface area, as consequences adsorption property develops in 15 wt% C@Co3Sb4O6F6/H2O2 for the elimination of methylene blue (MB). This favourable chemical adsorption process occurs with large maximum adsorption capacity (qmax = 58.41169 mg g-1), as evident from the Langmuir adsorption isotherm. Scavenger experiment confirms that the photocatalytic activities of the as-synthesised compounds were triggered by the active participation of the hydroxyl radical (.OH). The catalytic efficiencies of both parent and doped compounds are also established for the solvent-free Knoevenagel condensation reaction with 90 % yield at moderate temperature. Bacterial disinfection studies by the ‘Disc diffusion method’ confirm that Co3Sb4O6F6 shows better efficiency than the carbon doped compound against both Gram-positive and Gram-negative bacteria.

Studies of the Solvent-Free Knoevenagel Condensation over Commercial NiO compared with NiO Drived from Hydrotalcites

In this study, we compared the effect of the commercial NiO, synthesis NiAl-HT and NiO-HT drived from hydrotalcite in Knoevenagel condensation reaction. The NiAl-HT sample was synthesized by the coprecipitation method with a molar ratio M2+/M3+ = 2 at constant basic pH. X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) were utilized to identify crystalline phases present in NiAl-HT, NiO-HT and commercial NiO. The chemical composition of the obtained solids was determined by Atomic Absorption Spectroscopy (AAS). Other techniques, such as Thermogravimetric Thermal Analyzer (TGA), Scanning Electron Microscopy (SEM) and Brunauere Emmette Teller Method (BET) were also used. As well as the BET showed the increase of the specific surface for the solid NiO-HT. The performance of the catalysts were studied in Knoevenagel condensation of benzaldehyde with ethyl acetoacetate without solvent to synthesis of organic compounds such as intermediates of dihydropyridines derivatives. The influence of different parameters, such as catalyst amount, reaction temperature and reaction time were optimized for studied the activity, the selectivity and the stability of the solids. Catalytic activity was in its lowest in the presence of NiAl-HT (26% of benzaldehyde conversion) whereas the benzaldehyde conversion increased to 77% in case of NiO-HT which can be explained by the presence of the basic sites of the NiO-HT oxides, a high surface area and a small crystallite size. Therefore, the lower increase in benzaldehyde conversion was noticed using commercial NiO (84%), perhaps owing to its high purity. A reaction mechanism is proposed by using density functional method (DFT). Copyright © 2023 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

Synthesis of Altissimacoumarin D and Other Prenylated Coumarins and Their Ability to Reverse the Multidrug Resistance Phenotype in Candida albicans.

Azoles are the main antifungal agents employed in clinical practice to treat invasive candidiasis. Nonetheless, their efficacy is limited by fungal resistance mechanisms, mainly the overexpression of efflux pumps. Consequently, candidiasis has a worrisome death rate of 75%. One potential strategy to overcome efflux-mediated resistance is to inhibit this process. Ailanthus altissima is a Chinese tree that produces several active substances, including altissimacoumarin D. Due to the low yield of its extraction and the need to search for new drugs to treat candidiasis, this study aimed to synthesize altissimacoumarin D and its analogues, as well as evaluating their ability to reverse the resistance phenotype of Candida albicans. Coumarin isofraxidin was prepared via total synthesis through a solvent-free Knoevenagel condensation as the key step. Isofraxidin and other commercially available coumarins were alkylated with prenyl or geranyl groups to yield the natural product altissimacoumarin D and seven analogues. The antifungal activity of the coumarins and their ability to reverse the fungal resistance phenotype were assessed using microbroth methodologies. Toxicity was evaluated using erythrocytes and an in silico prediction. All compounds improved the antifungal activity of fluconazole by inhibiting efflux pumps, and ACS47 and ACS50 were the most active. None of the coumarins were toxic to erythrocytes. In silico predictions indicate that ACS47 and ACS50 may be safe for human use. ACS47 and ACS50 are promising candidates when used as adjuvants in the antifungal therapy against C. albicans-resistant strains.

Highly active zinc oxide-supported lithium oxide catalyst for solvent-free Knoevenagel condensation

Highly active zinc oxide-supported lithium oxide catalyst for solvent-free Knoevenagel condensation

Triazine-functionalized highly ordered hierarchically porous organic polymer with high CO2 uptake capacity and catalytic activity for microwave-assisted Knoevenagel condensation reaction

We report a new hierarchical meso-microporous organic co-polymer PDVTAT-1, synthesized using P123 as structure directing agent to produce ordered 2D hexagonal mesopores along with the in-built micropores by utilizing 2,4,6-triallyloxy-1,3,5-triazine and divinylbenzene monomers. The reaction was progressed via solvothermal radical polymerization using AIBN reaction initiator. A thorough characterization of the polymer was conducted employing powder X-ray diffraction study, N2 sorption, 13C CP MAS NMR, FT-IR and UV–vis spectroscopy, FE-SEM, HR-TEM, Thermogravimetric, CHN, and CO2 TPD-TCD analysis. Having a surface area of 1016 m2 g−1, surface basicity of 1.17 mmol g−1 and pore diameters of 1.54 nm (micropore) and 3.29 nm (mesopore), the polymer exhibited significantly good CO2 uptake capacities of 1.07 mmol g−1 and 5.75 mmol g−1 at 298 and 273 K temperature, respectively up to 1.0 bar pressure, with the heat of adsorption (Qst) value 48.74 kJ mol−1. Also, PDVTAT-1 was used as a reusable heterogeneous base catalyst for solvent-free Knoevenagel condensation reaction.

A Facile, Efficient and Solvent-Free Titanium (IV) Ethoxide Catalysed Knoevenagel Condensation of Aldehydes and Active Methylenes

: Titanium ethoxide has been employed as a novel and efficient reagent for the Knoevenagel condensation of aldehydes with active methylenes such as diethyl malonate and ethyl cyanoacetate under solvent free conditions to afford substituted olefins in high to excellent yields. The reaction is suitable for a variety of aromatic, aliphatic and heteroaromatic aldehydes with various active methylenes. Parallel to this, microwave irradiation has been utilized to achieve improved reaction rates and enhanced yields. Herein, we illustrated a convenient method for the preparation of α,β-unsaturated compounds using both conventional and microwave irradiation methods. An efficient and solvent free Knoevenagel condensation between aldehydes and active methylenes was developed using titanium ethoxide. The procedure proved to be successful with a wide range of substrates such as aromatic, aliphatic and heterocyclic aldehydes and various active methylenes to afford substituted olefins. The reaction was also carried out under microwave irradiation to accomplish the corresponding olefins with improved reaction rates, yields and cleaner reaction profiles.We have developed an efficient and novel methodology for the synthesis of olefinic compounds by Knoevenagel condensation under solvent-free conditions using titanium ethoxide, for the first time, as a reagent as well as a solvent. This method is appropriate for the synthesis of a variety of aromatic aldehydes containing various electron-donating and withdrawing groups, aliphatic and heteroaromatic aldehydes. The significant advantages offered by this methodology could be applied to various active methylenes in order to offer the corresponding Knoevenagel products. Thus, we believe that this method delivers high conversions, cleaner reaction profiles under solvent-free reaction conditions and shorter reaction times, all of which make it a very useful and attractive approach for the preparation of a wide range of substituted olefins.

Amino Acid Amide based Ionic Liquid as an Efficient Organo-Catalyst for Solvent-free Knoevenagel Condensation at Room Temperature

Ionic liquids of amino acid amide were synthesized and used as an efficient catalyst for solvent-free Knoevenagel condensation. Synthesized ionic liquids are an environmentally benign, inexpensive, metal free and plays the dual role of solvent as well as an efficient catalyst for Knoevenagel condensation. A wide range of aliphatic, aromatic and heteroaromatic aldehydes easily undergo condensation with malononitrile and ethyl cyanoacetate. The reaction proceeds at room temperature without using any organic solvent and is very fast with good to excellent yield. Additionally, the catalyst is easily separable and recyclable without loss of activity.

Synthesis and characterization of amine functionalized graphene oxide and scope as catalyst for Knoevenagel condensation reaction

Novel amine modified graphene oxide (APTES-GO) was prepared using organo silane (aminopropyltrimethoxysilane, APTES) and the material was fully characterized by PXRD, Raman, SEM, FTIR, and TEM. Successful grafting of the amine group over the graphene oxide (GO) surface was confirmed by FT-IR and TEM data. APTES-GO as heterogeneous catalyst demonstrated impressive activity for solvent-free Knoevenagel condensation reaction producing cinnamic acid with excellent conversion (94%) and selectivity (99%) at RT. The catalytic activity remained almost unchanged for four cycles and in fifth cycle conversion was 9% less.

Thermally decomposed mesoporous Nickel Iron hydrotalcite: An active solid-base catalyst for solvent-free Knoevenagel condensation

Thermal decomposition of co-precipitated NiFeHT materials led to the formation a mesoporous NiFeHT catalyst and we have demonstrated here its active role as solid and active catalyst for the Knoevenagel condensation reaction of various aldehydes with active methylene compounds (RCH2CN, where RCN or CO2Et). High product yields are obtained at moderate temperature under solvent-free conditions and the catalyst can be easily separated from the reaction mixture, simply by filtration and reused several times without a significant loss of its activity. Since these mesoporous metal oxides derived from the NiFe hydrotalcites, their basicity mediated abstraction of the acidic protons from the active methylene compounds was responsible for their catalytic activity under solvent-free conditions.

Tetrabutylphosphonium amino acid ionic liquids as efficient catalysts for solvent-free Knoevenagel condensation reactions

Five tetrabutylphosphonium amino acid ionic liquids ([P4444][AA]) were prepared, characterized, and used as catalysts for solvent-free Knoevenagel condensation reactions. The tetrabutylphosphonium prolinate ([P4444][Pro]) showed excellent catalytic activity and selectivity in Knoevenagel condensation reactions of active methylene compounds with various aromatic aldehydes, and all the yields of corresponding products were more than 85% under mild conditions. Furthermore, a plausible reaction mechanism for the excellent performance of [P4444][Pro] has been proposed, and [P4444][Pro] could be used repetitively at least six times without obvious decrease in activity and quantity.

Ball milling for the quantitative and specific solvent-free Knoevenagel condensation + Michael addition cascade in the synthesis of various 2-amino-4-aryl-3-cyano-4H-chromenes without heating

Various 2-amino-4-aryl-3-cyano-4H-chromenes have been quantitatively prepared by dry ball milling in the presence of catalytic Na2CO3. The orientation specificities are discussed; existing misattributions are pointed out and clarified by NMR.

Ultrasound-assisted synthesis of 2,4-thiazolidinedione and rhodanine derivatives catalyzed by task-specific ionic liquid: [TMG][Lac

BackgroundSynthesized arylidene derivatives of rhodanine and 2,4-thiazolidiendione have potent pharmacological activities, and these are also key substrates for the preparation of clinically used antidiabetics.FindingsSome 1,1,3,3-tetramethylguanidine-based task-specific ionic liquids (TSILs) 1a-1e were prepared and employed to the catalyzed solvent-free Knoevenagel condensation of 2,4-thiazolidinedione 3a and rhodanine 3b with a variety of aldehydes.ConclusionsBest results were obtained with 1,1,3,3-tetramethylguanidine lactate ([TMG][Lac]) 1c. The TSIL used can be easily recovered and recycled, yielding products 4–5 in excellent yields under ultrasonic environment without the formation of any side products or toxic waste.

室温无溶剂无催化剂下的Knoevenagel缩合反应研究

本文报道了芳香醛和丙二腈在室温无催化剂无溶剂下的Knoevenagel缩合反应，合成了系列苄叉基化合物，产率良好，并利用1HNMR和13CNMR等对合成的化合物结构进行了表征。结果表明，该方法没有使用催化剂和有毒有害的有机溶剂，具有反应条件温和，实验操作及产物后处理简单，产率高，对环境无污染等优点。 This paper reported the solvent-free Knoevenagel condensation of aromatic aldehydes and malononitrile at room temperature without catalyst, a series of benzylidene compounds were synthesized in high yields. Structure of all compounds was analyzed by 1HNMR, 13CNMR, and IR. The results showed that this method has advantages of mild reaction conditions and that the operation is simple, convenient post-processing, high yield, and friendly to environment.

A Practical Approach to New (5Z) 2-Alkylthio-5-arylmethylene-1-methyl-1,5-dihydro-4H-imidazol-4-one Derivatives

A practical protocol for the preparation of (5Z)-2-alkylthio-5-arylmethylene-1-methyl-1,5-dihydro-4H-imidazol-4-one derivatives is reported. The new compounds were obtained in good yield and stereoselectivity in two steps, namely a solvent-free Knoevenagel condensation under microwave irradiation, followed by an S-alkylation reaction with various halogenoalkanes.

Controllable acid-base bifunctionalized mesoporous silica: Highly efficient catalyst for solvent-free Knoevenagel condensation reaction

Abstract A controllable acid-base bifunctionalized mesoporous catalyst with acidic sites and basic sites in adjacent arrangements was prepared via an in situ cleavage of sulfonamide bond on synthetic process. During Knoevenagel condensation reaction of aromatic aldehydes and ethyl cyanoacetate under microwave irradiation in solid media, the mesoporous bifunctionalized catalyst Me-A/B-SBA-15 exhibited higher catalytic activity than those of the corresponding amine-functionalized catalyst and the randomly-arranged acid-base catalyst, showing obvious acid-base cooperativity.

Solid superbase derived from lanthanum–magnesium composite oxide and its catalytic performance in the knoevenagel condensation under solvent-free condition

We report for the first time the synthesis of a novel solid superbase that was derived from lanthanum–magnesium composite oxide and KOH through thermal treatment. The as-prepared material shows base strength (H–) above 26.5 and is a high-efficiency catalyst for solvent-free Knoevenagel condensation at room temperature. The results of the present study open up a new dimension for the use of composite oxides as new support materials in the synthesis of superbases.

Microwave-Assisted and Efficient Solvent-free Knoevenagel Condensation. A Sustainable Protocol Using Porous Calcium Hydroxyapatite as Catalyst

A sustainable Knoevenagel condensation of a series of aldehydes with malononitrile and ethyl cyanoacetate is described. The process is based on the combination of microwave activation and hydroxyapatite catalysis under solvent-free conditions. Products are obtained in and high yields after short reaction times. The effects of the specific surface of porous calcium hydroxyapatite and microwave activation are discussed.

Solvent-Free L-Proline Catalysed Condensation of Ethyl Cyanoacetate with Aldehydes

Solvent-free Knoevenagel condensation of ethyl cyanoacetate with aromatic aldehydes, catalysed by environmentally friendly silica gel supported L-proline under microwave irradiation is studied.