Application of molybdenum complexes for the oxidation of cyclohexane in acetonitrile, ionic liquid and supercritical CO2 media, a comparative study

Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

Ionic liquids (ILs) have unique physicochemical properties that make them advantageous for catalysis, such as low vapor pressure, non-flammability, high thermal and chemical stabilities, and the ability to enhance the activity and stability of (bio)catalysts. ILs can improve the efficiency, selectivity, and sustainability of bio(transformations) by acting as activators of enzymes, selectively dissolving substrates and products, and reducing toxicity. They can also be recycled and reused multiple times without losing their effectiveness. ILs based on imidazolium cation are preferred for structural organization aspects, with a semiorganized layer surrounding the catalyst. ILs act as a container, providing a confined space that allows modulation of electronic and geometric effects, miscibility of reactants and products, and residence time of species. ILs can stabilize ionic and radical species and control the catalytic activity of dynamic processes. Supported IL phase (SILP) derivatives and polymeric ILs (PILs) are good options for molecular engineering of greener catalytic processes. The major factors governing metal, photo-, electro-, and biocatalysts in ILs are discussed in detail based on the vast literature available over the past two and a half decades. Catalytic reactions, ranging from hydrogenation and cross-coupling to oxidations, promoted by homogeneous and heterogeneous catalysts in both single and multiphase conditions, are extensively reviewed and discussed considering the knowledge accumulated until now.

Peroxidative Oxidation of Cyclohexane Using 3d Metal Complexes with Hydrazone-Derived Ligands as Catalysts: Exploring (Un)Conventional Conditions

Two tetranuclear and two mononuclear Cu(II) complexes with arylhydrazones of malononitrile derived ligands (compounds 1–2 and 3–4, respectively), one trinuclear Co(II/III) complex with an arylhydrazone of acetoacetanilide (5) and one tetranuclear Zn(II) complex of 3-(2-carboxyphenyl-hydrazone)pentane-2,4-dione (6) were screened as potential catalysts in the peroxidative oxidation of cyclohexane by aqueous H2O2 in acetonitrile. The best results were attained in the presence of pyrazine-2-carboxylic acid (PCA) with 1 (26% yield, TON = 52.0) and with 2 (24%, TON = 48.0) after 4 h at 40 °C. In the presence of complexes 5 and 6, no oxygenated products were detected in the studied conditions. The employment of non-conventional conditions like supercritical carbon dioxide (scCO2) as reaction medium or microwave (MW) irradiation was assessed for complexes 1 and 2. After 6 h in acetonitrile–scCO2, at 50 °C and with HNO3 as promoter, only 17% yield was achieved using 1 as catalyst, and 21% using 2. Total yields of oxygenates up to 14 (with 1) and 13% (2) and TOFs of 56.0 and 52.0 h−1, respectively, were obtained working under MW irradiation at 70 °C and for the much shorter time of 0.5 h.

A comprehensive and updated review of studies on the oxidation of cyclohexane to produce ketone-alcohol (KA) oil

Oxidation of cyclohexane is an essential chemical reaction for the industrial manufacture of cyclohexanol and cyclohexanone. These two compounds, together known as ketone–alcohol (KA) oil, are the main feedstock for nylon 6 and nylon 6,6 productions. Several types of catalysts and reaction conditions have been used for cyclohexane oxidation. This paper presents a thorough literature review of catalytic materials used for cyclohexane oxidation to produce KA oil using oxygen, air and other oxidizing agents as well as utilizing different solvents. This review covers research and development reported over the years 2014–2020. This review aims to comprehend the type of catalysts, solvents, oxidants and other reaction parameters used for the oxidation of cyclohexane. Three types of cyclohexane oxidation processes namely thermocatalytic, photocatalytic and microwave-assisted catalytic have been reported. The results of the review showed that metal and metal oxide loaded silica catalysts performed excellently and provided high selectivity of KA oil and cyclohexane conversion. The use of peroxides is not feasible due to their high price compared to air and oxygen. Gold nanoparticles supported on silica performed with high selectivity and good conversion. The use of hydrochloric acid as an additive was found very effective to enhance the photocatalytic oxidation of cyclohexane. Water on the catalyst surface enhanced the reactivity of the photocatalysts since it helps in the generation of hydroxyl radicals.

Oxidative functionalization of C–H compounds induced by the extremely efficient osmium catalysts (a review)

In recent years, osmium complexes have found applications not only in thecis-hydroxylation of olefins but also very efficient in the oxygenation of C–H compounds (saturated and aromatic hydrocarbons and alcohols) by hydrogen peroxide as well as organic peroxides.