Selective aerobic oxidation of cyclic ethers to lactones over Au/CeO2 without any additives

Gold-Catalyzed Lactone Synthesis: Advancements and Insights

Lactones represent a class of fundamental structural motifs ubiquitous in nature, holding significance across diverse scientific domains such as pharmaceuticals, natural products, drug discovery, and industry. Despite their simplicity, the synthesis of lactones has garnered considerable interest due to their pivotal roles. Gold, traditionally regarded as a noble metal, has emerged as an efficient catalyst, challenging conventional perceptions. The utilization of gold in lactone synthesis has captivated researchers, leading to the development of numerous effective methodologies. Motivated by this, we present a comprehensive compilation of reports on the gold-catalyzed synthesis of lactones, encompassing literature till date.

Fabricated Gamma-Alumina-Supported Zinc Ferrite Catalyst for Solvent-Free Aerobic Oxidation of Cyclic Ethers to Lactones

The aim of this work was to fabricate a new heterogeneous catalyst as zinc ferrite (ZF) supported on gamma-alumina (γ-Al2O3) for the conversion of cyclic ethers to the corresponding, more valuable lactones, using a solvent-free method and O2 as an oxidant. Hence, the ZF@γ-Al2O3 catalyst was prepared using a deposition-coprecipitation method, then characterized using TEM, SEM, EDS, TGA, FTIR, XRD, ICP, XPS, and BET surface area, and further applied for aerobic oxidation of cyclic ethers. The structural analysis indicated spherical, uniform ZF particles of 24 nm dispersed on the alumina support. Importantly, the incorporation of ZF into the support influenced its texture, i.e., the surface area and pore size were reduced while the pore diameter was increased. The product identification indicated lactone compound as the major product for saturated cyclic ether oxidation. For THF as a model reaction, it was found that the supported catalyst was 3.2 times more potent towards the oxidation of cyclic ethers than the unsupported one. Furthermore, the low reactivity of the six-membered ethers can be tackled by optimizing the oxidant pressure and the reaction time. In the case of unsaturated ethers, deep oxidation and polymerization reactions were competitive oxidations. Furthermore, it was found that the supported catalyst maintained good stability and catalytic activity, even after four cycles.

Selective Oxidation of Tetrahydrofuran to Gamma-Butyrolactone over Spinel ZnFe2O4 Nanoparticle Catalyst

The selective oxidation of tetrahydrofuran (THF) to gamma-butyrolactone (GBL) on spinel ZnFe2O4 nanoparticles (ZFNPs) was investigated. The catalyst was prepared with the coprecipitation method and characterized by FTIR, XRD, TEM, SEM, EDS, TGA, XPS, and BET surface area. The characterization techniques showed that a nonuniform spherical spinal oxide with an average particle size of 26 nm was formed. The oxidation reaction was carried out using hydrogen peroxide as an oxidizing agent under solvent-free conditions. GC-MS analysis revealed that the main product was GBL. 2-hydroxytetrahydrofuran (THF-2-OH), gamma-hydroxybutyric acid (GHBA), and gamma-hydroxybutaldehyde (GHBAl) were obtained as minor products. The effects of different reaction parameters, such as temperature, H2O2/THF mole ratio, catalyst dose, reaction time, and reusability, were evaluated. A 47.3% conversion of THF with an 88.2% selectivity of GBL was achieved by conducting the reaction at 80 °C for nine hours using a 1:1 mole ratio of H2O2/THF. A slight increase in the conversion degree was attained at higher temperatures; however, an over-oxidation process was observed as the temperature exceeded 80 °C. The catalyst remained effective and stable over four reuses.

Nano-scale minerals in-situ supporting CeO2 nanoparticles for off-on colorimetric detection of L-penicillamine and Cu2+ ion

Realizing the high value-added utilization of cheap minerals in environmental catalysis has important practical significance. Herein, four nano-scale minerals, namely halloysite (Hal) nanotubes, palygorskite (Pal) nanorods, and montmorillonite (Mon) and hydrotalcite (LDH) nanosheets, were selected for in-situ supporting CeO₂ nanoparticles (NPs) by a facile one-pot hydrothermal method. Among various nanocomposites (NCs), CeO₂/Pal behaves the highest peroxidase-like activity, attributing to larger surface area for uniformly dispersing CeO₂ NPs and more exposed active oxygen vacancy (O_vac) defects. A novel off-on colorimetric strategy was constructed for detecting toxic L-penicillamine (LPA) and Cu²⁺ ion with limit of detections (LODs) of 8.37 and 9.80 μM, respectively. Density functional theory (DFT) calculations show that the O_vac defect on CeO₂(111) surface can catalyze the heterolytic cleavage of H₂O₂ into H₂O and oxygen radical (•O), instead of being two hydroxyl radicals (•OH) on clean surface. It can also act as trapping site for O₂ and H₂O adsorption, improving the oxygen affinity and hydrophilicity of CeO₂/Pal. This study provides a feasible strategy for designing mineral-based nanozymes and an insight into the possible catalytic mechanism.