Imidazolized Activated Carbon Anchoring Phosphotungstic Acid as a Recyclable Catalyst for Oxidation of Alcohols With Aqueous Hydrogen Peroxide

Keggin-type phosphotungstic acid (HPW) supported on imidazolyl-activated carbon (AC-COIMI-HPW) catalysts was prepared, which was used to catalyze the oxidation of benzyl alcohol with aqueous H₂O₂. In the presence of AC-COIMI-HPW, the benzyl alcohol conversion of 90.2% with 91.8% selectivity of benzaldehyde was obtained at 90°C for 6 h in an acetonitrile aqueous solution. The catalyst exhibited an outstanding performance for the oxidation of various benzyl alcohols and aliphatic alcohols. In addition, the catalyst could be easily recovered and reused five times without significant deactivation. The characterization results showed that HPW was chemically bonded on the surface of the carbon material through an ionic bond. It is proposed that the combination of the imidazole cation with the HPW anion could not only tune the redox catalytic properties of the PW anion but also enhance the compatibility of the catalyst in the reaction medium, thereby improving the catalytic performance.

A novel base-metal multifunctional catalyst for the synthesis of 2-amino-3-cyano-4H-chromenes by a multicomponent tandem oxidation process

A novel base-metal multifunctional nanomagnetic catalyst is prepared by the immobilization of tungstate anions onto γ-Fe₂O₃ supported with imidazolium moieties. The (γ-Fe₂O₃-Im-Py)₂WO₄ was fully characterized using FT-IR, XPS, TEM, FESEM, ICP, TGA, VSM and XRD and used as a multifunctional heterogeneous catalyst for the synthesis of 2-amino-3-cyano-4H-chromenes via a multicomponent tandem oxidation process starting from alcohols under solvent-free conditions. During this process, tungstate catalyzes the oxidation of a wide range of alcohols in the presence of TBHP as a clean source. The in-situ formed aldehydes are condensed with malononitrile and β-dicarbonyl compounds/naphthols/4-hydroxycumarin through promotion by pyridine and imidazolium moieties of the catalyst. By this method, a variety of 2-amino-3-cyano-4H-chromenes are generated in good to high yields from alcohols as inexpensive and easily available starting materials. The catalyst is recovered easily by the aid of an external magnetic field and reused in five successive runs with insignificant decreasing activity.

Hydroxyl-assisted selective epoxidation of perillyl alcohol with hydrogen peroxide by vanadium-substituted phosphotungstic acid hinged on imidazolyl activated carbon

Vanadium-substituted phosphotungstic acid hinged on imidazolyl activated carbon catalyzed efficiently and stably the selective epoxidation of perillyl alcohol with H2O2.

Cytotoxicity and Membrane Permeability of Double-Chained 1,3-Dialkylimidazolium Cations in Ionic Liquids

We have evaluated ionic liquids based on double-chained 1-alkyl-3-octylimidazolium cations ([C_nC₈IM]⁺, n = 2, 4, 6, 8, 10, 12) for their cytotoxicity toward various cell lines. The toxicity of ionic liquids was correlated to their ability to partition into and permeabilize phosphocholine (POPC)- or phosphoglycerol (POPG)-based large unilamellar vesicles. Membrane partitioning of ionic liquids was assessed using the ζ-potential measurements, and membrane permeability was determined using fluorescence-based dye leakage assays. Both cytotoxicity and membrane permeability of these ILs were found to increase in a sigmoidal fashion with increasing chain length on the N1 atom (n in [C_nC₈IM]⁺) cations. These results were compared with those for ionic liquids based on single-chained 1-alkyl-3-methylimidazolium cations ([C_n+8C₁IM]⁺), carrying a similar number of carbon atoms but as a single alkyl chain. Our studies show that ionic liquids containing double-chained cations are relatively less cytotoxic and membrane-permeabilizing than the cations bearing a single long alkyl chain.

Ionic-liquid-modified CMK-3 as a support for the immobilization of molybdate ions (MoO42-): Heterogeneous nanocatalyst for selective oxidation of sulfides and benzylic alcohols

A nanometric carbon CMK-3 modified with octylimidazolium ionic liquid and MoO₄^2- as a new hybrid catalyst was synthesized. The study is the first to report a successful immobilization of MoO₄⁼ on the CMK-3/OctIm as a hybrid nanocatalyst. A variety of analytical methods were utilized to determine the properties of the structure and morphology of the synthesized nanocatalyst [CMK-3/Im/MoO₄^2-]. The analytical techniques were transmission electron microscopy (TEM), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), inductively coupled plasma (ICP), X-ray diffraction (XRD), N₂ isotherms (BET), IR spectroscopy and thermogravimetric analysis (TGA). CMK-3/OctIm/MoO₄^2- hybrid catalyst demonstrated a considerable catalytic activity. It is a recyclable nanocatalyst that is utilized to chemoselectively oxidize different types of sulfides to the corresponding sulfoxides and benzylic alcohols to aldehydes using the green oxidant, hydrogen peroxide (H₂O₂) in high-yields. With a little leaching and variation in activity, it is possible to recover and reuse the catalyst frequently. A combination of molybdate anion and the CMK-3 order mesoporous carbon resulted in an improvement in the performance of catalysis and ease of separation for the reaction procedure.

Hydrogen Peroxide as a Green Oxidant for the Selective Catalytic Oxidation of Benzylic and Heterocyclic Alcohols in Different Media: An Overview

Among a plethora of known and established oxidant in organic chemistry, hydrogen peroxide stands in a special position. It is commercially and inexpensively available, highly effective, selective, and more importantly it is compatible with current environmental concerns, dictated by principles of green chemistry. Several chemicals or their intermediates that are important in our daily life such as pharmaceuticals, flavors, fragrances, etc. are products of oxidation of alcohols. In this review, we introduce hydrogen peroxide as an effective, selective, green and privileged oxidant for the catalyzed oxidation of primary and secondary benzylic and heterocyclic alcohols to corresponding carbonyl compounds in different media such as aqueous media, under solvent-free conditions, various organic solvent, and dual-phase system.

Needle ball-like nanostructured mixed Cu-Ni-Co oxides: Synthesis, characterization and application to the selective oxidation of sulfides to sulfoxides

A mixed nano-metal oxides of Cu-Ni-Co has been synthesized. Several characterization techniques (EDS, XRD, TEM, and SEM) have been used to provide insight into the nature and structure of the catalyst. The size of this mixed metal oxide is 22 nm. The SEM images indicate that the sample with spherical particles, of which spherical assembly is comprised of elongated rod/needle-like subunits pointing radially outward, creates a needle ball-like structure. To efficiently catalyze the selective oxidation of sulfide towards sulfoxide, this heterogeneous catalyst uses an oxidizing agent (hydrogen peroxide- H₂O₂) and a solvent (acetonitrile) in mild conditions. The influence of reaction temperature and sulfide/oxidant molar ratio was evaluated with respect to sulfide conversion and chemoselectivity towards the sulfoxide product. Under optimized conditions, product yields in the range from 70 to 97% were obtained.