Reaction Conditions Research Articles

Rational design of nitrogen-doped carbon for palladium catalysts in hydrogenation of hydrazo compounds

We synthesized CN11, a carbon nitride material rich in sp3 hybrid graphitic nitrogen (sp3-N), employing a facile oxalic acid-assisted melamine molecular assembly strategy. CN11 promoted the formation of Pd nanoparticles (NPs) predominantly exposing {200} facets, termed Pd/CN11-2. This facet-specific configuration significantly boosted hydrogen adsorption, leading to notable improvements in catalytic activity. Compared to Pd/XC-72-2 and Pd/g-C3N4-2, Pd/CN11-2 exhibited a remarkable two-fold and nineteen-fold increase in catalytic yield for hydrazo compound hydrogenation, respectively. Pd/CN11-2 also demonstrated robust performance across a range of reaction conditions, maintaining excellent yield. This study emphasizes the critical role of tailored support structures in controlling Pd NPs facets, thereby enhancing hydrogenation efficiency. It provides valuable insights for advancing the industrial application of Pd-based catalysts, underscoring the importance of strategic support modulation for optimizing catalytic performance.

EMIM] [OAc]: An Efficient Ionic Liquid Medium for the Synthesis of New 4-(furan/pyrrole/thiophene-2-yl)-3, 4-dihydro-1H-chromeno [4,3-d] pyrimidine-2,5-diones and Molecular Docking Studies

Abstract: An efficient synthesis of Chromeno[b]pyrimidine derivatives 4 has been achieved by treating 4-hydroxy-2H-chromen-2-one 1, furan-2-carbaldehyde / 1H-pyrrole-2-carbaldehyde/ thiophene-2- carbaldehyde 2, and urea/thiourea 3 at 65-70 °C for 90-120 min using 1-Ethyl-3-methylimidazolium acetate as ionic liquid and medium with good yields 86-90%. This synthetic method has numerous advantages, including high yields, a simple protocol, environmental friendliness, brief reaction times, and mild reaction conditions. Using a catalytically active ionic liquid as the medium eliminates the need for a catalyst and a solvent. In this study, the docking score of the synthesized compounds was found to be between -8 to -9 kcal/mol similar to the co-crystal. Additionally, the compounds maintained their amino acid interactions with Tyr 281 (coagulation protein; 6WV3) and Thr 179 (tubulin polymerization protein; 5LYJ.pdb).

Exploring the role of solvents in structural regulation during ultrasonic synthesis of Co/Ni-layered double hydroxide for oxygen evolution reaction

Cobalt-based layered double hydroxides (LDHs) are highly sought after by researchers due to their low-cost, high efficiency and stability for oxygen evolution reaction (OER) in water electrolysis. The OER performance of these LDHs is closely related to their morphology and electronic structure. However, there is a lack of theory on how to control reaction conditions to regulate the morphologies. In this paper, the growth mechanism of LDH prepared in different solvents is thoroughly studied. Consequently, the Co/Ni-LDHs exhibiting a 3D hierarchical flower-like structure were synthesized with normal alcohol as a solvent, meanwhile, the thickness of the LDHs can be controlled by the molecular weight of the normal alcohol. By adjusting the suitable Co/Ni ratio and solvent, the Co/Ni0.050-LDH-Me was synthesized and exhibited excellent OER performance. At 10 mA cm−2, the overpotential of Co/Ni0.050-LDH-Me is 307 mV, and the Tafel slope is 76.5 mV dec−1.

Synergistic effects of hydroxyl and tertiary amine in the catalytic carbonatization of epoxides with CO2 at atmospheric pressure

Fixation of carbon dioxide is a key issue for the sustainable synthesis of chemical compounds. A catalyst system for the preparation of cyclic carbonates by the fixation of carbon dioxide (CO2) onto epoxides is presented. This system is designed for easy application due to the availability of the compounds on an industrial scale as well as moderate reaction conditions. Notably, it avoids the use of metal-halogen catalysts and instead employs a tertiary amine as the catalytic center, in conjunction with an alcohol acting as a hydrogen bond donor (HBD). The kinetics of the cycloaddition reaction between epoxides and CO2 were thoroughly investigated using IR spectroscopy. Remarkably, optimization of the amino-to-alcohol group ratio and the amine structure was carried out to enhance the overall performance of the catalyst system showing a synergistic effect between the tertiary amine and the hydroxyl. Most notably, this entire process is conducted without the use of solvents and operates at ambient pressure, underscoring its significant ecological advantages.

An improved synthesis of alkyl AMP esters

Enzymes belonging to the Acyl-CoA/NRPS/Luciferase (ANL) superfamily of enzymes, are significant targets in drug development. One member of this superfamily is Acetyl-CoA Synthetase (ACS). This enzyme is an emerging target for the treatment of various infectious diseases and cancer. Alkyl AMP esters have emerged as potent inhibitors of ACS. Previous methods for synthesizing these esters often involved water-based reactions or necessitate purification through reverse phase prep-HPLC or ion-exchange chromatography. To address these challenges, we developed a new approach utilizing 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) to couple 5′-adenylic acid to the corresponding alcohol, utilizing triethylamine as the base. This method yielded primary, secondary, unsaturated, and cyclic alcohols in excellent yields. Importantly, we optimized the reaction conditions to achieve excellent yield and purity without the need for reverse phase prep-HPLC or ion exchange chromatography. Instead, purification was achieved through silica gel chromatography using Biotage ® Sfar spherical silica gel.

Tecoma stans intermediated green synthesis of copper oxide nanoparticles, its characterization, paracetamol degradation and biological activities

The main objective of the present research work is to green synthesize copper oxide nanoparticles (CuO NPs) and to study its potential against various enmities to safeguard our environment and health. Based on this approach, preparation of CuO NPs was accomplished using four different volumes (10, 25, 40, and 50 mL of leaves extract) of Tecoma stansleaves extract. Moreover, all the synthesized CuO NPs were characterized using XRD, UV–visible, FTIR, and SEM with EDS analysis. From the XRD pattern, the structures of all the synthesized CuO NPs were found to be monoclinic in phase. According to the UV–visible studies, the calculated band gap energy values for all the prepared CuO NPs were higher compared to bulk CuO, which was 1.2 eV. Further, the FTIR results showed the presence of CuO bond and SEM with EDS analysis revealed the surface morphology of CuO NPs andthe presence of elements showing the purity of synthesized CuO NPs, respectively. The optimized condition for the preparation of CuO NPs were 50 mL of leaves extract mixed with 50 mL of double distilled water (CuO4 NPs) showed a spheroidal morphology as evident from the HRTEM images. XPS analysis used to find the oxidation state of detected elements especially for copper and oxygen. The predicted BET and Langmuir surface area of CuO4 NPs were calculated to be 40.305 m2/g and 5074.12 m2/g respectively. Photocatalytic degradation of paracetamol (PCM) using CuO4 NPs was investigated, and the effect of parameters such as pH, initial concentration of PCM solution, and catalyst dosage were studied under UV light irradiation. The highest removal of 95.15 % had been achieved at 120 min under optimized reaction conditions. Additionally, CuO4 NPs also exhibited exemplary antibacterial activity against bacillus subtilis bacteria with a zone of inhibition of 26 mm. Further, in vitro cytotoxic behaviour of CuO4 NPs was estimated using A549 cancer cells by MTT assay. Thus, the green synthesis of CuO NPs using Tecoma stans leaves extract has the capacity to participate in photocatalytic and biological activities.

Expanding the high-pH range of the sucrose synthase reaction by enzyme immobilization

The glycosylation of an alcohol group from a sugar nucleotide substrate involves proton release, so the reaction is favored thermodynamically at high pH. Here, we explored expansion of the alkaline pH range of sucrose synthase (SuSy; EC 2.4.1.13) to facilitate enzymatic glycosylation from uridine 5’-diphosphate (UDP)-glucose. The apparent equilibrium constant of the SuSy reaction (UDP-glucose + fructose ↔ sucrose + UDP) at 30 °C increases by ∼4 orders of magnitude as the pH is raised from 5.5 to 9.0. However, the SuSy in solution loses ≥80% of its maximum productivity at pH ∼7 when alkaline reaction conditions (pH 9.0) are used. We therefore immobilized the SuSy on nanocellulose-based biocomposite carriers (∼48 U/g carrier; ≥ 50% effectiveness) and reveal in the carrier-bound enzyme a substantial broadening of the pH-productivity profile to high pH, with up to 80% of maximum capacity retained at pH 9.5. Using reaction by the immobilized SuSy with automated pH control at pH ∼9.0, we demonstrate near-complete conversion (≥ 96%) of UDP-glucose and fructose (each 100mM) into sucrose, as expected from the equilibrium constant (Keq = ∼7 × 102) under these conditions. Collectively, our results support the idea of glycosyltransferase-catalyzed synthetic glycosylation from sugar nucleotide donor driven by high pH; and they showcase a marked adaptation to high pH of the operational activity of the soybean SuSy by immobilization.

Regeneration of bulk and silica-supported gallium oxide catalysts applied in the dehydrogenation of methanol to formaldehyde and hydrogen by reaction-oxygen regeneration cycles and oxygen pulses in the feed

The oxygen-free dehydrogenation of methanol to formaldehyde and hydrogen is a potential alternative to the established industrial oxidative dehydrogenation yielding aqueous formaldehyde solutions. Advantages are the production of anhydrous formaldehyde and of hydrogen as a valuable coupled product. However, fast deactivation of the catalyst occurs under the high-temperature reaction conditions mainly due to coking, which can be overcome by applying oxygen at a temperature high enough to allow fast oxidation of the carbon deposits but low enough to prevent the loss of Ga. From an engineering point of view, a stable reaction temperature in the catalyst bed and a high H2 yield have to be maintained, requiring that the catalyst enables methanol dehydrogenation, but not the oxidation of hydrogen to water. Thus, two modes of regeneration of GaOx-based catalysts were investigated using reaction − oxygen regeneration cycles and oxygen pulses in the feed. When using bulk Ga2O3 as catalyst and applying optimized reaction-regeneration cycles, a formaldehyde yield of 51 % and a hydrogen yield of 45 % at a stable methanol conversion of 65 % were achieved, whereas undiluted O2 pulsed into the feed every 30 s resulted in a continuous formaldehyde yield of 40 % and a hydrogen yield of 35 % at a stable methanol conversion of 59 % with water yields below 2 % and 4 %, respectively. The effects of the two operation modes on stability and product distribution are discussed in terms of the carbon removal rate from the surface, refilling of oxygen vacancies and parasitic reactions in the presence of oxygen. Specifically, the consumption of O2 did not lead to excessive water formation but preferentially effected the oxidation of the carbon deposits to CO and CO2.

Synthesis of α‐NiS Decorated Fe3S4 Nanohybrid Composite and Its Heterogeneous Fenton Catalysis for Dye Degradation

AbstractGreigite (Fe3S4) and millerite (NiS) are important transition metal sulfides that exhibit light‐driven Fenton catalytic activity. In absence of light, they show limited activity. To utilize these properties without relying on light, we synergized these sulfides to prepare a composite Fe3S4–NiS (FSNS). Under fixed reaction conditions, the composite demonstrated excellent Fenton activity, degrading 93% of fast green dye (FG) and 98.1% of eriochrome black T dye (EBT) within a short reaction time. The mechanism involves electron transfer from the reduced sulfur state (S2−) in both NiS and Fe3S4 to the higher oxidation states of the metal ions viz. Fe3+and Ni3+ to facilitate the redox cyclization in the Fenton process. The catalyst showed high stability for five cyclical tests by recovering it from solution with an external magnet.

Photocatalytic One-Pot Three-Component Reaction for the Regioselective Synthesis of Bromo-Substituted Pyrazoles.

A photocatalytic three-component cascade reaction of readily available enaminones, hydrazines, and CBr4 for the synthesis of bromo-substituted pyrazoles in one pot has been demonstrated. This strategy involves intermolecular C-N/C-Br bond formation and represents an efficient approach to the construction of 4-bromo-substituted pyrazoles with high regioselectivity, broad substrate scope, good functional group tolerance, convenient operation, and mild reaction conditions. Mechanistic investigations show that this reaction proceeds via intermolecular cyclization of enaminones with hydrazines, followed by a regioselective bromination of pyrazoles using CBr4 as a "Br" source.

Enhancing stability of industrial Cu-based catalysts under harsh reduction reaction conditions with silica armor protection

Cu-based catalysts are widely employed in various industrial processes, yet they are susceptible to deactivation due to sintering. Inhibiting the sintering deactivation of Cu nanoparticles has been a long-standing challenge for Cu-based catalysts. In this study, we propose a novel silica armor strategy to effectively protect Cu-based catalysts from sintering. Bioethanol dehydrogenation was selected as the test reaction, with the resulting products of acetaldehyde and hydrogen displaying strong reducing properties. After a 160-hour reaction period, the Cu nanoparticles in Cu/ZnO protected by a silica armor demonstrated exceptional stability, as the sintering of the Cu nanoparticles was effectively prevented. High resolution transmission electron microscope (HRTEM), X-ray absorption (XAS), and theoretical calculations were carried out to disclose the reasons for the stabilization of Cu nanoparticles by silica armor. The physical confinement created by the silica armor and the interactions between silicon species and Cu species efficiently suppressed the sintering of Cu particles. Furthermore, our research has showcased the potential application of the silica armor strategy on commercially available catalysts, highlighting its ability to effectively prevent the sintering of Cu particles on high-Cu content Cu/ZnO/Al2O3 industrial catalysts.

Fe3O4@SiO2‐APA‐Amide/Imid‐NiCl2 as a New Nano‐Magnetic Catalyst for the Synthesis of 4H‐Pyrimido[2,1‐b]benzothiazole Derivatives via MCRs Under Solvent‐Free Conditions

AbstractThis study presents the synthesis and characterization of a novel nano‐magnetic catalyst, Fe3O4@SiO2‐APA‐amide/imid‐NiCl2, designed for the efficient production of 4H‐pyrimido[2,1‐b]benzothiazole derivatives under environmentally friendly, solvent‐free conditions. The catalyst combines magnetic Fe3O4 nanoparticles with a silica shell and functionalized amide and imidazole groups, which enhance its catalytic activity and stability. By optimizing the reaction conditions, we achieved high yields of the target compounds while minimizing the environmental impact. The catalyst's magnetic properties facilitate easy separation and recovery, making it an attractive option for sustainable organic synthesis. The successful synthesis of the catalyst was confirmed through comprehensive characterization techniques, including X‐ray diffraction (XRD), Fourier‐transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The results demonstrate that Fe3O4@SiO2‐APA‐amide/imid‐NiCl2 is a highly effective and reusable catalyst for the environmentally friendly synthesis of biologically relevant pyrimido[2,1‐b]benzothiazole derivatives, contributing to the advancement of green methodologies in organic chemistry.

β‐Cyclodextrin‐SO3H as a Supramolecular Catalyst for Efficient Greener Synthesis of Substituted Bis(6‐aminouracil‐5‐yl)methanes in Water

AbstractA simple, straightforward, and highly efficient greener approach for synthesizing bis(6‐aminouracil‐5‐yl)methane derivatives was developed by employing β‐cyclodextrin‐SO3H as supramolecular catalyst in water at 100 °C. A total of 16 bis(6‐aminouracil‐5‐yl)methanes were synthesized via a one‐pot reaction between substituted aromatic aldehydes, 6‐amino‐1,3‐dimethyluracil, and 10% β‐cyclodextrin‐SO3H in water with 84%–92% yield within 20–120 min. The salient features of this protocol included water as green solvent, β‐cyclodextrin‐SO3H as recyclable supramolecular catalyst, mild reaction conditions, easy isolation of pure products, and good to excellent yields.

Oxygen vacancies–elusive but common catalytic key defects for thermal upgrading of CO2 to CH4, CO and CH3OH

Single carbon products (C1 compounds) are simple but important chemicals in the road towards energy transition. Catalytic conversion of CO2 with H2 (desirably renewable) can be performed over reducible oxides supporting transition metals to obtain products such as CH4, CO and MeOH. Oxygen vacancies (O-vacancies), which are inherent defects of reducible metal oxides, play an enormous role in driving the catalytic performance (activity, selectivity, stability) for the desired reactions. Yet, the assessment of O-defects at realistic conditions is often complex. Only few techniques can provide direct evidence for their existence and influence in CO2 activation. Among them, electron paramagnetic spectroscopy (EPR), Raman spectroscopy, scanning probe microscopies (SPM) and environmental transmission electron microscopy (ETEM) are nowadays the most informative. In most cases, however, the measurements require reaction conditions far away from CO2 valorization applications. Although great efforts have been fruitful in explaining and demonstrating the huge importance of O-vacancies in CO2 catalysis, still ambiguous or erroneous interpretations about structure-function correlations involving O-vacancies are found in literature, especially, when information is not properly gathered, e.g., by O 1s ex-situ X-ray photon spectroscopy (XPS). Moreover, despite the recognized importance of O-vacancies for CO2 valorization, critical literature compilations about their effects in thermal processes are scarce. Herein, we attempt to contribute in closing this gap by integrally encompassing representative investigations on the thermo-catalytic production of CH4, CO and MeOH. Particularly, we emphasize in the proper selection of assessment tools (direct/indirect) to unambiguously establish structure-function relationships to design optimized O-defective catalysts for the targeted compounds.

Enhanced catalytic performance of ethyl-levulinate to γ-valerolactone: Effect of copper loading on Ni/KIT-5 catalyst

A facile wet impregnation method was employed to prepare a bimetallic Ni–Cu catalyst on a mesoporous KIT-5 support, keeping the nickel loading constant (5 wt%) while varying the copper wt.% (xCu, where x = 8, 10, 12, 14). Several physico-chemical techniques, including X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), temperature-programmed desorption of ammonia (NH3-TPD), temperature-programmed reduction of hydrogen (H2-TPR), and X-ray photoelectron spectroscopy (XPS), were utilized for catalyst characterization. An environmentally friendly NiCu bimetallic-supported catalyst system was developed in response to many problems, including metal leaching, sintering, and cost. A mesoporous KIT-5 silica support with a large surface area was used. The hydrogenation of ethyl levulinate to gamma-valerolactone was studied utilizing a high-pressure stirred reactor and a range of reaction temperatures (120–160 °C), hydrogen pressures (10–30 bar), and reaction periods. Various catalysts were used in the investigation. Among all tested catalysts, the 12Cu–5Ni/KIT-5 one shows excellent activity. The best GVL yield is 84% at a conversion of 100% after 8 h of treatment at 150 °C and 25 bar H2 pressure; the promotion is also 76.1%. Optimization of reaction conditions was shown to correlate the physicochemical parameters of the catalyst with its activity.

Organometallic Ru(III) Catalysts for α-Alkylation of Carbonyl Compounds using Alcohols: Mechanistic Insights via Detection of Key Intermediates.

Three novel cyclometalated ruthenium complexes ([Ru.L(9)] [Ru.L(10)] and [Ru.L(11)]) featuring azo functionalities were synthesized and characterized using a variety of spectroscopic techniques, namely FT-IR, electronic absorption spectroscopy, and ESI-MS. Representative solid-state structures of the acquired complexes were determined through X-ray crystallography. These complexes were evidenced to be efficient catalysts for the synthesis of various α-alkylated compounds utilizing simple acetophenone derivatives with easily affordable and economically viable alcohols, which were isolated and characterized via 1H and 13C NMR spectroscopy. The optimum reaction conditions were found by employing toluene as solvent, potassium tert-butoxide as base at 115 oC temperature utilizing 0.8 mol% of catalyst [Ru.L(10)]. The yield of the desired compounds found to be in the range of 83 - 97%. Additionally, mass spectrometry provided insights into the in-situ generated ruthenium hydride and ruthenium alkoxy intermediates, shedding light on the catalytic mechanism.

Activation of peroxymonosulfate by Fe based metal organic framework for selective degradation of phenol in water

Phenol is a common pollutant in various wastewater, which is required to be removed to a certain standard before the wastewater can be discharged. Persulfate-based advanced oxidation processes (PS-AOPs) are an effective technology for phenol removal, with efficacy contingent upon the activation methods and materials employed. In this study, Fe-based metal-organic frameworks (Fe-MOFs) constructed with carboxylic acid as a ligand were synthesized by a solvothermal method, which can form chelates with ferrous ions. Fe-MOFs showed the activity similar to the homogeneous catalyst thus improving their activation efficiency, and can be used to activate peroxymonosulfate (PMS) for phenol degradation in water. The effects of catalyst dosage, PMS and phenol concentration, temperature, and pH on the degradation efficiency were investigated. Under the optimum reaction conditions, the 96 % of phenol can be rapidly removed in 5 min. SO4·− was determined as the primary radical. Fe species on Fe-MOFs acted as the key active sites. Density functional theory (DFT) analysis suggested enhanced charge redistribution, fostering electron-rich sites that facilitate electron transfer in AOPs, thus boosting phenol degradation. The Fe-MOFs/PMS system enables iron recycling and efficient phenol degradation in water, indicating the potential for phenol-contaminated water treatment.

On-DNA Mannich Reaction for DNA-Encoded Library Synthesis.

The β-amino ketones produced through the Mannich reaction hold significant potential as candidates for various drugs. In this study, we optimized on-DNA Mannich reaction conditions and applied them to investigate the reactions of DNA-conjugated aldehydes with various amine and ketone building blocks. The developed on-DNA Mannich reaction preserved the DNA integrity and established viable routes for library production. These results underscore the potential of the Mannich reaction in DNA-encoded library (DEL) synthesis.

Dynamic stable Pt13 clusters anchored on isolated ZnOx nanorafts for efficient cycloparaffin dehydrogenation

Methylcyclohexane (MCH) has attracted wide attention as liquid organic hydrogen carriers for safe alternative and high gravimetric hydrogen density. Pt13 cluster with its fascinating structure exhibits excellent performance in cycloalkane dehydrogenation reactions accompanied by balanced C-H cleavage capability. However, the controllable synthesis of stable Pt13 clusters under reaction conditions remains challenging. Herein, we successfully synthesized low-coordinated Pt13 clusters anchored by isolated ZnOx nanorafts on silanol-rich self-pillared zeolite nanosheets (SP-S-1). In situ XAFS spectra combined with theoretical calculations revealed that Pt13 clusters exhibited strong interfacial Pt-Zn bonds and reduced d-band center through orbital hybridization (Zn 3d - Pt 5d), facilitating C-H bond cleavage and toluene desorption. The optimized catalyst exhibited superior MCH dehydrogenation activity and durability, achieving a hydrogen production rate of 3457.9 mmolH2 gPt−1 min−1 at 400 ˚C and maintaining stable for over 100 hours. This study precisely synthesizes dynamic stable Pt13 clusters and provides valuable insights into the dehydrogenation mechanism.

Iron-Catalyzed Cross-Dehydrogenative Coupling of para-Quinone Methides with Formamides: In Situ Activation of C(sp2)-H Bonds.

A novel and straightforward method for the iron-catalyzed regioselective cross-dehydrogenative coupling of para-quinone methides (p-QMs) with formamides has been developed, facilitated by the in situ activation of the C(sp2)-H bonds of the formyl and alkenyl substituents via a radical strategy. This method does not require the preactivation of the substrates, and it can accommodate a wide range of p-QMs and formamides under the optimized reaction conditions, resulting in the formation of the expected C-7 acetamides-functionalized para-quinone methides with moderate to good yields. The control experiments revealed that the reaction follows the fundamental equation of second-order kinetics. Additionally, an exploration of the Hammett effect was undertaken to elucidate the impact of the substituents for the reaction. In combination with the DFT calculation, a plausible reaction mechanism was proposed through meticulously controlled experiments.