Chemical Methodologies

Abstract The isolation of components of interest is important in many industries because it impacts the quality of the product, the economics of the process, and the environment. Supercritical fluid extraction (SFE) is a modern method of extraction that is more versatile and eco-friendlier than traditional methods, as it is highly selective and offers fast mass transfer along with high solvent recovery. It is used in the pharmaceutical, nutraceutical, food processing, cosmetics, and natural products industries. In this review, the basic principles of SFE and the important operating parameters—temperature, pressure, solvent flow rate, supercritical fluid type, particle size, extraction time, and feed moisture content—are discussed concerning extraction yield and efficiency. Both thermodynamics (phase behavior, solubility, and density effects) and kinetic factors (mass transfer rates and diffusion limitations) are included to discuss how these factors affect the driving force of the process. It is shown that with proper selection of parameters, yield, selectivity, and even sustainability can be improved, thereby making SFE more competitive for the recovery of valued compounds. This information provide a useful guide to help researchers and industry experts aiming to design, scale up, and apply effective SFE systems across different uses.

Abstract The oxidative dehydrogenation (ODH) of propane represents a promising pathway for the selective production of propylene, a key intermediate in the petrochemical industry. Recent advances focus on the use of metal-based zeolite catalysts due to their high activity, selectivity, and stability. The incorporation of carbon dioxide (CO₂) as a mild oxidant offers environmental and economic advantages, such as reducing greenhouse gas emissions and avoiding the use of molecular oxygen, which can cause over-oxidation. This review summarizes laboratory-scale studies on various metal-based zeolite catalysts for propane ODH in the presence of CO₂, highlighting catalyst preparation methods, characterization techniques, catalytic performance, reaction mechanisms, and the role of CO₂ in reaction pathways. Challenges and future perspectives for catalyst design and process optimization are also discussed.

Abstract N-arylation of nitrogen-containing compounds remains a key challenge in organic synthesis due to issues related to selectivity, harsh conditions, and limited substrate scope. Herein, an efficient copper-catalyzed protocol is reported for the synthesis of 1,1-diaryl hydrazine derivatives via the coupling of aryl boronic acids with hydrazine hydrate. The reaction proceeds under mild, ligand-free conditions without the need for strong bases, an inert atmosphere, or expensive reagents. A broad range of aryl boronic acids bearing electron-donating and electron-withdrawing groups is well tolerated, affording the corresponding symmetric diaryl hydrazines in moderate to excellent yields. The method also demonstrates good chemoselectivity, minimizing over-arylation and polymerization side reactions commonly associated with free hydrazine use. This operationally simple and scalable procedure provides convenient access to structurally diverse 1,1-diaryl hydrazines—key intermediates in pharmaceuticals, agrochemicals, and functional materials. The practical features and broad applicability of this method make it a valuable addition to existing N-arylation strategies, with the potential for future extension to unsymmetrical hydrazine derivatives and heteroaryl substrates.

Abstract Imidazolinones are known to react with nucleophiles in acidic media through intermediate iminium ion formation. In contrast, their interactions with electrophiles in acid-catalyzed systems are uncommon and have been scarcely documented. In this work, it was demonstrated that imidazolin-2-ones can function as nucleophiles in acid-promoted reactions with N-(4,4-diethoxybutyl)sulfonylamides, facilitating the regioselective preparation of 4-(pyrrolidin-2-yl)imidazole-2-ones. The target products were obtained in moderate to good yields (45–71%), with reactivity influenced by substituent effects.

Abstract In this study, synthetic 1,4-cis-polyisoprene rubber (SKI-3) was modified with a phospholipid concentrate to bring its properties closer to those of natural rubber. The phospholipid concentrate (a mixture of phospholipids and vegetable oils) was introduced into the SKI-3 polymerizate during the degassing stage (when the rubber is extracted from the isopentane polymerization solution) at a dosage of 3–7 parts per hundred parts of rubber (phr, by weight). The rubber was then extracted from the solution and dried at 80 °C to constant weight. An identical sample of synthetic rubber without phospholipid was prepared as a control. Infrared spectroscopy confirmed the immobilization of phospholipid fragments onto the polyisoprene macromolecules, as evidenced by new absorption bands at 1,742 cm⁻¹ and 3,320 cm⁻¹ for carbonyl and hydroxyl groups, respectively, in the modified rubber. The effect of phospholipid content on the rubber’s properties was also examined. At an optimal loading of 5 phr, the modified rubber exhibited higher cohesive strength. The Mooney viscosity of the rubber compounds increased at 3 and 5 phr loadings but decreased at 7 phr. Thermogravimetric analysis (TGA) was used to assess thermal stability. The phospholipid-modified rubber showed enhanced thermal stability compared to the control. Overall, introducing phospholipids at the polymer extraction stage effectively enhanced the synthetic rubber’s physicomechanical properties and thermal stability, making its performance more comparable to that of natural rubber.

Abstract Rice husk, an abundant waste from the agro-industrial sector, contains residual vegetable oil rich in unsaturated fatty acids. In this study, an eco-friendly and efficient strategy is presented for converting rice husk biomass into monoglycerides, compounds of significant industrial importance. The process begins with extraction of rice husk in a semi-automatic Soxhlet apparatus (ASV-6M) using ethyl acetate, which demonstrated the highest extraction efficiency among six tested solvents, yielding up to 2.82% oil from rice husk. The extracted oil was subjected to a catalytic glycerolysis reaction under moderate pressure and temperature conditions (220 °C for 4 h) in the presence of KOH, resulting in a monoglyceride content of approximately 68.87%. The obtained mixture was purified using a two-step method involving crystallization in an acetone–water solution, followed by column chromatography on silica gel, which afforded monoglycerides with a purity of up to 93%. Structural and compositional analyses were carried out by gas chromatography–mass spectrometry (GC–MS) and infrared (IR) spectroscopy, confirming the presence of key esters such as monoglycerides of palmitic and oleic acids. Mass spectrometry data confirmed the molecular weights corresponding to the structures of the monoglycerides, while the IR spectra showed characteristic absorption bands corresponding to ester and hydroxyl functional groups.

Abstract The current study provides a new leaching method for extracting valuable metals, such as uranium, vanadium, molybdenum, and rare earth metals (REMs), from black shale ores. Initial characterization indicated that these metals are encapsulated in hard “carbon-silica shells,” presenting severe extraction challenges. A novel low-temperature sintering process is considered in this work with ammonium hydrosulfate at 350 °C for 60 minutes, much lower than the conventional process of over 800 °C. The devised treatment effectively ruptures the protective shell, converting metal constituents into soluble forms. Subsequent leaching yielded good recovery rates: uranium (93.3%), vanadium (81.7%), molybdenum (82.2%), and REMs (78.3%). Thermogravimetric analysis revealed the stepwise decomposition mechanism and emission profiles upon sintering. The leaching parameters (solid-liquid ratio, temperature, time, and solution concentration) were optimized for maximum metal recovery, along with selective sorption conditions (pH, redox potential, and duration) and desorption variables. Additionally, the cost-effective production routes for vanadium concentrate were specified as ammonium metavanadate, molybdenum concentrate as calcium molybdate and REM concentrate as carbonates, instead of depending on high-pressure or high-temperature processes. Solid residue carbon flotation enrichment was accompanied by a recovery yield of 89.0% by weight of carbon, enabling enhanced utilization of the entire resource. Altogether, the adopted approaches offer a closed-loop, energy-saving pathway to the efficient recovery of the rare and essential metals from the black shale ore.