Search Results (360)

A series of Zn complexes containing guanidine– and amidine–phenolate ligands were synthesized and evaluated as catalysts for the polymerization of rac-lactide at 130 °C, under solvent-free conditions, giving rate constants in the range of 0.71–4.37 × 10^–4 s^–1. Polymerization under identical conditions with the guanidine– and amidine–phenol proligands themselves used as catalysts gave values in the range of 0.30–2.45 × 10^–4 s^–1. The stereoselective production of polylactic acid from either the Zn complexes or the proligands was limited (P_r = 0.47–0.62). The molecular weight of the polymers was lower than expected for living polymerizations due to chain transfer and/or transesterification but were comparable to those obtained in control experiments with Sn(Oct)₂. Full article

Isoxazole-based molecules constitute a crucial category of heterocyclic compounds with wide-ranging applications across pharmaceutical development, advanced materials, and pesticide synthesis. Traditional synthetic approaches for isoxazole derivatives frequently encounter challenges such as extended reaction periods, severe operating conditions, and reliance on toxic solvents. As an eco-friendly alternative, sonochemistry has emerged as a promising approach for organic synthesis, offering enhanced reaction efficiency, reduced energy consumption, and improved yields. In this context, this review introduces the recent advancements in ultrasound-assisted strategies for the synthesis of isoxazole-scaffolds and their derivatives. Various methodologies are discussed, including multi-component reactions, catalytic systems, and solvent-free protocols. The integration of ultrasound not only accelerates reaction kinetics but also minimizes byproduct formation and enables the use of green solvents or catalysts. Key advantages such as shorter reaction durations, higher atom economy, and operational simplicity are emphasized. This work underscores the potential of sonochemical techniques to revolutionize isoxazole-based molecule synthesis, aligning with the principles of sustainable and green chemistry. Full article

Catalytic upgrading of pyrolysis oils is an important step for producing replacement hydrocarbon-rich liquid biofuels from biomass and can help to advance pyrolysis technology. Catalysts play a pivotal role in influencing the selectivity of chemical reactions leading to the formation of main compounds in the final upgraded liquid products. The present work involved a systematic study of solvent-free catalytic reactions of cyclohexanone in the presence of hydrogen gas at 160 °C for 3 h in a batch reactor. Cyclohexanone can be produced from biomass through the selective hydrogenation of lignin-derived phenolics. Three types of catalysts comprising undoped NbOPO₄, 10 wt% NiO/NbOPO₄, and 30 wt% NiO/NbOPO₄ were studied. Undoped NbOPO₄ promoted both aldol condensation and the dehydration of cyclohexanol, producing fused ring aromatic hydrocarbons and hard char. With 30 wt% NiO/NbOPO₄, extensive competitive hydrogenation of cyclohexanone to cyclohexanol was observed, along with the formation of C₆ cyclic hydrocarbons. When compared to NbOPO₄ and 30 wt% NiO/NbOPO₄, the use of 10 wt% NiO/NbOPO₄ produced superior selectivity towards bi-cycloalkanones (i.e., C₁₂) at cyclohexanone conversion of 66.8 ± 1.82%. Overall, the 10 wt% NiO/NbOPO₄ catalyst exhibited the best performance towards the production of precursor compounds that can be further hydrodeoxygenated into energy-dense aviation fuel hydrocarbons. Hence, the presence and loading of NiO was able to tune the activity and selectivity of NbOPO₄, thereby influencing the final products obtained from the same cyclohexanone feedstock. This study underscores the potential of lignin-derived pyrolysis oils as important renewable feedstocks for producing replacement hydrocarbon solvents or feedstocks and high-density sustainable liquid hydrocarbon fuels via sequential and selective catalytic upgrading. Full article

Mechanochemical and transition-metal-catalyzed reactions of alkynes, exhibiting significant advantages like short reaction time, solvent-free, high yield and good selectivity, were considered to be green and sustainable pathways to access functionalized molecules and obtained increasing attention due to the superiorities of mechanochemical processes and the reactivities of alkynes. The ball milling and CuI-catalyzed Sonogashira coupling of alkyne and aryl iodide avoided the use of common palladium catalysts. The mechanochemical Rh(III)- and Au(I)-catalyzed C–H alkynylations of indoles formed the 2-alkynylated and 3-alkynylated indoles selectively. The mechanochemical and copper-catalyzed azide-alkyne cycloaddition (CuAAC) between alkynes and azides were developed to synthesize 1,2,3-triazoles. Isoxazole could be formed through ball-milling-enabled and Ru-promoted cycloaddition of alkyne and hydroxyimidel chloride. In this review, the generation of mechanochemical and transition-metal-catalyzed reactions of alkynes was highlighted. Firstly, the superiority and application of transition-metal-catalyzed reactions of alkynes were briefly introduced. After presenting the usefulness of green chemistry and mechanochemical reactions, mechanochemical and transition-metal-catalyzed reactions of alkynes were classified and demonstrated in detail. Based on different kinds of reactions of alkynes, mechanochemical and transition-metal-catalyzed coupling, cycloaddition and alkenylation reactions were summarized and the proposed reaction mechanisms were disclosed if available. Full article

The semi-synthesis of the (5R,7R,11bR)-9-(di(1H-indol-3-yl)methyl)-4,4,7,11b-tetramethyl-1,2,3,4,4a,5,6,6a,7,11,11a,11b-dodecahydrophenanthro[3,2-b]furan-5-yl acetate was performed via a pseudo-multicomponent reaction involving a double Friedel–Crafts alkylation between the natural product-derived aldehyde 6β-acetoxyvouacapane and the corresponding indole. The transformation was carried out under solvent-free mechanochemical conditions using mortar and pestle grinding, with ZnCl₂ as the catalyst. Structural elucidation of the target compound was accomplished using 1D and 2D NMR spectroscopy (¹H, ¹³C, COSY, HSQC, and HMBC), FT-IR, and high-resolution mass spectrometry (HRMS). Full article

Several benzothiazole (BT) derivatives have recently been explored in medicinal chemistry, and they are frequently reported in the literature. The interest in this kind of heterocyclic compounds and their structural hybrids has been increasing, as shown by several reviews reported over the last decade. In this context, we found that about 70 articles related to the synthesis of BT derivatives that studied their biological activities were published in the last five years. From this, we prepared a review on the synthesis and biological activity studies about this topic. In this bibliographic review it was found that medicinal chemists also explore BT derivatives in search of anticancer and anti-Alzheimer’s candidates. This review comprehends 70 articles, published between 2020 and 2024, related to the synthesis of BT derivatives with the purpose of assessing their biological activities. On the other hand, BT derivatives have been explored as molecular species that perform two or more biological actions, called multifunctional drugs. Some accounts related to the structure–activity relationship which provide a framework for drug discovery and design are also discussed. The synthetic methods of BT synthesis include the use of biocatalysts, solvent-free conditions, photocatalysts, and catalysts supported on nanoparticles. Studies also explore renewable energy sources such as microwave, UV, and visible-light and mechanochemical sources. Full article

This work studies the effect of mesostructured silica–zirconia–tungstophosphoric acid (SiO₂-ZrO₂-TPA) composites used as catalysts in the synthesis of nifedipine by the Hantzsch methodology. The selectivity for nifedipine is determined, along with that of secondary products that may form depending on the reaction conditions. The materials were synthesized via the sol–gel method and characterized by N₂ adsorption–desorption isotherms, infrared spectroscopy (FT-IR), ³¹P solid-state nuclear magnetic resonance (NMR-MAS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray photoelectron spectra (XPS), and potentiometric titration. The characterization results from the XPS spectra showed that as the Si/Zr ratio drops, the Si-O-Si signal size decreases, while the Zr-O signal size increases. Characterization by titration indicated that an increase in the total acidity of the material, resulting from support modification with tungstophosphoric acid (H₃PW₁₂O₄₀, TPA), enhances the reaction yield. The catalytic activity in the solvent-free Hantzsch reaction was evaluated under thermal heating and microwave irradiation. The experiments conducted at 80 °C achieved a maximum yield of 57% after 4 h of reaction using the Si20Zr80TPA30 catalyst (50 mg), while by microwave heating, the yield significantly improved, reaching 77% in only 1 h of reaction. This catalyst exhibited stability and reusability without significant loss of activity up to the third cycle. Depending on the type of material and the reaction conditions, it is possible to modify the selectivity of the reaction, obtaining a 1,2-dihydropyridine isomeric to nifedipine. Reaction intermediates and other minor secondary products that may be formed in the process were also evaluated. Full article

The enzyme ω-transaminase (ω-TA) has garnered significant attention due to its capacity to catalyze the synthesis of chiral amines with high efficiency. Nevertheless, the lack of stability of ω-TA and the difficulty of recycling and reuse are still challenges that limit its application. This study developed a novel magnetic nanocellulose composite carrier (NNC@Fe₃O₄@Ni), synthesized from microcrystalline cellulose via low-eutectic solvent treatment, amine modification, and metal hybridization. The NNC@Fe₃O₄@Ni was characterized by FTIR, XPS, XRD, BET, and VSM. Additionally, the performance and catalytic behavior of the immobilized enzyme were investigated. The results revealed that NNC@Fe₃O₄@Ni exhibited a high specific surface area, superparamagnetism, and dual-site functionality (amine/Ni²⁺). Response Surface Methodology (RSM) optimized the carrier-enzyme interaction parameters, yielding optimal immobilization conditions: a mass ratio of 50.8 mg g⁻¹, temperature of 12.5 °C, and duration of 58.6 min, achieving 82.91% enzyme activity recovery. Compared to free enzymes, the immobilized variant demonstrated enhanced catalytic stability, with expanded optimal pH (9.0) and temperature (30 °C). Thermal stability assessments showed 84.39% activity retention after 5 h at 30 °C and 90.30% residual activity post-120 h storage. The catalyst maintained >80% efficiency over 10 reuse cycles. These findings confirm the efficacy of magnetic nanocellulose carriers in enhancing ω-TA stability, reusability, and catalytic performance, offering a viable strategy for industrial biocatalytic processes. Full article

Lignin, a complex aromatic biopolymer abundant as waste in biorefineries and the pulp and paper industry, holds significant potential for valorization. This study presents the oxidative depolymerization of Lignoboost lignin (LB) using H₂O₂ under mild, solvent- and catalyst-free, inherently acidic conditions at 50–70 °C. The process aimed to produce functionalized low-molecular-weight oligomers, retaining aromaticity, and aliphatic dicarboxylic acids, rather than complete monomerization. The depolymerized LB was rich in aromatic dimers-trimers (68.6 wt.%) with high functionalization (2.75 mmol/g OHphen, 3.58 mmol/g OHcarb, 19.5 wt.% of H in -CH=CH-), and aliphatic dicarboxylic acids (53.4 wt.% of monomers). Acidic conditions provided higher depolymerization and functionalization than alkaline, alongside simplified product recovery. The process was also successfully applied to Kraft lignin, demonstrating versatility and robustness even with higher polymeric content feedstocks. The optimized conditions were scaled up (×25), improving efficiency and yielding Mw 464 g/mol and Đ 1.3. As proof of concept, the scaled-up product underwent radical crosslinking, resulting in a new biopolymer with higher thermal stability than LB (54.2 wt.% residual mass at 600 °C versus 36.1 wt.%). This green, scalable process enhances lignin valorization by producing functionalized low-molecular-weight lignin oligomers and dicarboxylic acids that can be used independently or together to form crosslinked networks. Full article

Methodologies for the effective fabrication of phosphinothioates, phosphonothioates, and phosphorothioates have always been of great interest due to their widespread application in many research fields. We present here a solvent-free reaction system for the synthesis of above compounds without any catalysts or additives, directly using disulfides with diarylphosphine oxides, dialkylphosphites, and phosphinates as substrates. Most of the target compounds were obtained in nearly quantitative yields by heating at 50 °C for 5–10 min or stirring at room temperature for 3 h. The products were efficiently separated via a water extraction operation, simultaneously recovering the by-product thiols. This mild and practical coupling protocol was also employed to prepare phosphinoselenoates from the corresponding diselenides with good yields. Full article

A series of Pd/g-C₃N₄ catalysts were synthesized using different graphitic carbon nitride precursors, and were found to exhibit significant variations in catalytic performance for solvent-free selective catalytic oxidation of benzyl alcohol. Through comprehensive characterization (XRD, N₂-BET, ICP-AES, TEM, and XPS), the experimental results found that the nitrogen chemical configuration and surface Pd²⁺concentration critically determined the catalytic efficiency. Among the various nitrogen species, N-(C)₃-type nitrogen demonstrated the strongest influence on catalytic activity, which was positively correlated with its abundance in g-C₃N₄ matrices. In particular, g-C₃N₄ derived from dicyandiamide contained the highest N-(C)₃ type nitrogen content. When serving as Pd nanoparticle support, this material simultaneously achieved the best Pd²⁺ surface concentration and catalytic performance compared to the other g-C₃N₄-supported catalysts. Full article

Quinoline, a heterocyclic scaffold of paramount importance in medicinal and industrial chemistry, has garnered significant attention due to its versatile applications. Traditional synthetic methods, dating back over a century, have evolved into innovative strategies leveraging catalytic C–H bond activation, transition-metal-free protocols, and photo-induced oxidative cyclization. Recent advancements highlight the synergistic roles of catalysts, oxidants, and solvents in enhancing molecular reactivity and reaction efficiency. This review systematically summarizes state-of-the-art oxidative annulation techniques for quinoline synthesis, emphasizing mechanistic insights and practical applications. Full article

Polyhydroxyurethanes (PHUs) synthesized from cyclic carbonates are promising alternatives to conventional polyurethanes due to their advantageous isocyanate-free synthesis and reprocessability characteristics. While many studies focus on PHUs derived from five-membered cyclic carbonates (5CCs) for more sustainable synthesis routes, PHUs from six-membered cyclic carbonates (6CCs) exhibit enhanced reactivity towards amines. Their reprocessability is facilitated by the presence of hydroxyl groups along the polymer chain, enabling transcarbamoylation reactions. However, since non-catalyzed transcarbamoylation is typically a sluggish reaction, catalysts are often required to enhance network reprocessability. This study presents a life cycle assessment (LCA) of PHU-5CC and PHU-6CC syntheses, with catalysts, for recycling applications targeting end-of-life scenarios. Environmental impact categories, including climate change, particulate matter, fossil resource depletion, mineral and metal resource use and freshwater eutrophication, were evaluated. Sensitivity analyses were also conducted to assess key variables. Our results indicate that PHUs from 6CCs show a higher environmental footprint due to their solvent-intensive synthesis process. Despite the increased reactivity and shorter reaction times associated with the 6CC monomer, these benefits do not fully offset the environmental impacts of the synthesis process. In conclusion, this study highlights potential improvements for future PHU synthesis, such as solvent-free processes, metal-free catalysts and optimized reaction monitoring. Full article

This work aims to explore the influence of crystal phase engineering on the photocatalytic hydrogen evolution activity of Ru/C₃N₄ systems. By precisely tuning the combination of Ru precursors and reducing solvents, we successfully synthesized Ru co-catalysts with distinct crystal phases (hcp and fcc) and integrated them with C₃N₄. The photocatalytic hydrogen evolution experiments demonstrated that hcp-Ru/C₃N₄ achieved a significantly higher hydrogen evolution rate (24.23 μmol h⁻¹) compared to fcc-Ru/C₃N₄ (7.44 μmol h⁻¹), with activity reaching approximately 42% of Pt/C₃N₄ under the same conditions. Photocurrent and electrochemical impedance spectroscopy analyses revealed that hcp-Ru/C₃N₄ exhibited superior charge separation and transfer efficiency. Moreover, Gibbs free energy calculations indicated that the hydrogen adsorption energy of hcp-Ru (ΔG_H* = −0.14 eV) was closer to optimal compared to fcc-Ru (−0.32 eV), enhancing the hydrogen generation process. These findings highlight that crystal-phase engineering plays a critical role in tuning the electronic structure and catalytic properties of Ru-based systems, offering insights for the design of highly efficient noble metal catalysts for photocatalysis. Full article

In the 21st century, sustainable agriculture is expected to become a major contributor to food security and improved nutrition. Amine–epoxide-based materials have great potential for use in agriculture due to their tunable physicochemical features, which are dependent on the concentration and composition of the monomers. In this work, catalyst-free green synthesis, using only water as a solvent, was performed to obtain a nanocarrier (TGel) capable of transporting nutrients after seed priming. The synthesis was based on the opening of the epoxy ring by nucleophile attack, using an amine-terminated polyether. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) techniques showed the spherical morphology of the particles, which ranged in size from 80 nm (unloaded TGel) to 360 nm (zinc-loaded TGel), respectively. Theoretical bonding analysis revealed that Zn cation species from the ZnSO₄ source interact with the polymer via σ-bonds, whereas EDTA forms hydrogen bonds with the polymer, thereby enhancing noncovalent interactions. Micro X-ray fluorescence (μ-XRF) and energy-dispersive X-ray fluorescence spectroscopy (EDXRF) provided details of the distributions of Zn in the seed compartments and shoots of cucumber plants after seed priming and plant growth, respectively. The use of the Zn-loaded TGels did not affect the physiology of the cucumber plants, as indicated by the photosynthetic efficacy, chlorophyll, and anthocyanin indices. Full article