Design of Glycerol-Based Solvents for the Immobilization of Palladium Nanocatalysts: A Hydrogenation Study

Renaissance in Alkyne Semihydrogenation: Mechanism, Selectivity, Functional Group Tolerance, and Applications in Organic Synthesis

Alkenes constitute a significant class of chemical compounds with applications in the bulk, pharmaceutical, or perfume industry. Among the known methods of olefin production, semihydrogenation of the C-C triple bond seems to be the most straightforward one. Nonetheless, the success of this reaction requires full control over diastereoselectivity, eradication of a parasitic process of over-reduction or migration of the C-C double bond formed, and achieving satisfactory functional-group compatibility. The review demonstrates developments in the field of alkyne semihydrogenation over the period 2010-2022, with selected papers published in 2023 and 2024, emphasizing solutions to the above-mentioned limitations. We discuss mechanistic aspects of this transformation, including those related to unconventional systems. The review includes examples of applications of alkyne semihydrogenation in organic synthesis, confirming the considerable utility of this process. Finally, strategies to enhance catalyst selectivity are summarized. For the reader's convenience, we provided a graphical guidebook to catalytic systems, illustrating the efficiency of the particular method.

Physical-chemical transformations for the remediation and valorization of hexachlorocyclohexanes (HCHs) including lindane: A review

The production of the former insecticide lindane (γ-HCH) resulted in the generation of vast quantities of hexachlorocyclohexanes (HCH) residues, creating one of the most significant environmental challenges related to persistent organic pollutants in the world. This contamination is present today in different scenarios, including stockpiles and highly concentrated mixed waste, contaminated surface soils, subsoil, and waters. In particular, Dense Non-Aqueous Phase Liquids (DNAPLs) represent challenging subsurface and groundwater contamination. This review provides a comprehensive and critical overview of the physical-chemical methodologies and remediation projects reported in the literature for addressing lindane contamination through separation, transformation, disposal, and valorization approaches. The available physicochemical techniques include dehydrochlorination, oxidation, reduction, substitution, isomerization, as well as electrochemical, photochemical, sonochemical, plasma, and other high energy treatments. Key aspects, such as advantages and limitations, remediation effectiveness, technological maturity, scalability, estimated costs, and applicability to different contamination scenarios are thoroughly analyzed for each method. The review culminates in a detailed comparison of these methodologies for various contamination contexts, providing valuable insights for the identification of optimal solutions to this global environmental challenge. In addition, the review assesses, for the first time, the potential for valorization of the products formed during HCH treatment or remediation. This aspect highlights the opportunity to transform HCH residues into higher value-added chemicals, thereby enhancing the circular economy of the remediation process. Finally, the integration of physicochemical methods with separation and biological tools offers a holistic perspective that underscores the importance of comprehensive strategies for addressing HCH contamination effectively and sustainably.

Assessment of oxidative stress biomarkers in Palaemon varians exposed to deep eutectic systems

In recent years, there has been extensive research within the scientific community on deep eutectic systems due to their remarkable versatility in solubilizing diverse substances and serving as effective solvents in catalytic processes. While initially regarded as non-toxic, a comprehensive toxicological assessment is essential to comprehend their behavior within organisms. In this study, seven distinct systems, composed of N,N,N-triethyl-N-(2,3-dihydroxypropyl)ammonium chloride (N00Cl) and glycerol-derived ethers with alkyl chains of varying lengths (100, 200, 3F00, 300, 3i00, and 400), in a 1:2 molar ratio were investigated for their aquatic toxicity in shrimp (Palaemon varians). The assessment involved analyzing oxidative stress biomarkers such as glutathione S-transferase, glutathione peroxidase, catalase, superoxide dismutase, total antioxidant capacity (TAC), and lipoperoxidation (MDA content). Results show an odd-even effect for LC50 values being N00Cl-300, the system showing higher values. Regarding oxidative stress, an imbalance between reactive oxygen species (ROS) and antioxidant capacity in the organisms has been observed, suggesting significant toxicity to shrimps due to the changes in oxidative stress biomarkers at high concentrations. However, at 100 mg/l all systems can be considered environmentally safe, and no negative impacts are expected on aquatic ecosystems.

A Ligand-Free Approach towards Coumarin Analogs via Natural Deep Eutectic Solvent-Mediated Suzuki-Miyaura Coupling

A ligand-free approach for the Suzuki-Miyaura cross coupling reaction using Natural Deep Eutectic Solvents (NaDES) towards coumarin analogs is described. A model reaction between the synthetically prepared 3-(4-acetyloxy-phenyl)-6-bromo-4-methyl-coumarin (3b) and phenylboronic acid was performed in five different NaDES as well as in pure glycerol, using two inorganic bases and palladium catalysts. The reaction proceeded smoothly in Choline Chloride/Glycerol (ChCl/Gly) and Betaine/Glycerol (Bet/Gly) NaDES at 90 °C in 24 h, affording the desired product in high yields up to 95%. The combination of K2CO3, Pd(OAc)2 and ChCl/Gly NaDES provided optimum yields and high purity of the desired compounds, while the solvent was successfully recycled and reused up to two times. The developed methodology is applicable to boronic acids bearing various substituents. The formation of palladium nanoparticles in the reaction mixture was observed, and the size of the nanoparticles was associated with the reaction yield. In addition, in all the glycerol-based NaDES, an effective removal of the acetyl group of the acetyloxy-coumarin analogs was observed; thus, it is noteworthy that the Suzuki-Miyaura coupling and the deacetylation reaction were achieved in one pot. The ten novel coumarin derivatives synthesized were structurally characterized using 1D and 2D NMR spectroscopy and were tested for their cytotoxicity against the A431 squamous cancer cell line, presenting significant activity.

Novel Catalyst Composites of Ni- and Co-Based Nanoparticles Supported on Inorganic Oxides for Fatty Acid Hydrogenations

In the quest to develop nanometrically defined catalytic systems for applications in the catalytic valorization of agri-food wastes, small Ni-based nanoparticles supported on inorganic solid supports have been prepared by decomposition of organometallic precursors in refluxing ethanol under H₂ atmosphere, in the presence of supports exhibiting insulating or semi-conductor properties, such as MgAl₂O₄ and TiO₂, respectively. The efficiency of the as-prepared Ni-based nanocomposites has been evaluated towards the hydrogenation of unsaturated fatty acids under solvent-free conditions, with high selectivity regarding the hydrogenation of C=C bonds. The influence of the support on the catalytic performance of the prepared Ni-based nanocomposites is particularly highlighted.

Deep Eutectic Solvents as à-la-Carte Medium for Transition-Metal-Catalyzed Organic Processes

Our society is facing a tremendous challenge to become more sustainable in every sphere of life. Regarding the chemical industry, one of the most significant issues to be addressed is the use of volatile organic compounds (VOCs) as solvents because they are petrol-derived and most of them are toxic and flammable. Among the possible solutions, deep eutectic solvents (DESs) have emerged as sustainable alternatives to VOCs in organic catalyzed transformations and other fields. The advantages of these new reaction media are not only related to their more benign physical and chemical properties and, for most of them, their renewable sources but also due to the possibility of being recycled after their use, increasing the sustainability of the catalyzed process in which they are involved. However, their use as media in catalytic transformations introduces new challenges regarding the compatibility and activity of known catalysts. Therefore, designed catalysts and "à-la-carte" DESs systems have been developed to overcome this problem, to maximize the reaction outcomes and to allow the recyclability of the catalyst/media system. Over the last decade, the popularity of these solvents has steadily increased, with several examples of efficient metal-catalyzed organic transformations, showing the efficiency of the catalysts/DES system, compared to the related transformations carried out in VOCs. Additionally, due to the inherent properties of the DES, unknown transformations can be carried out using the appropriated catalyst/DES system. All these examples of sustainable catalytic processes are compiled in this review.

Green Synthesis of Pd Nanoparticles for Sustainable and Environmentally Benign Processes

Among transition metal nanoparticles, palladium nanoparticles (PdNPs) are recognized for their high catalytic activity in a wide range of organic transformations that are of academic and industrial importance. The increased interest in environmental issues has led to the development of various green approaches for the preparation of efficient, low-cost and environmentally sustainable Pd-nanocatalysts. Environmentally friendly solvents, non-toxic reducing reagents, biodegradable capping and stabilizing agents and energy-efficient synthetic methods are the main aspects that have been taken into account for the production of Pd nanoparticles in a green approach. This review provides an overview of the fundamental approaches used for the green synthesis of PdNPs and their catalytic application in sustainable processes as cross-coupling reactions and reductions with particular attention afforded to the recovery and reuse of the palladium nanocatalyst, from 2015 to the present.