Simple and Green Adipic Acid Synthesis from Cyclohexanone and/or Cyclohexanol Oxidation with Efficient (NH4)xHyMzPMo12O40 (M: Fe, Co, Ni) Catalysts

The oxidation of cyclohexanone and/or cyclohexanol to adipic acid (AA) was performed at 90 °C with a reaction time of 20 h, in the presence of H2O2 as oxidant and transition metal substituted ammonia polyoxometalates of formula, (NH4)xHyMzPMo12O40 (M: Fe, Co, or Ni,  and x = 2.5 or 2.28) as catalysts.  The catalytic results showed that the AA yield is sensitive to the transition metal nature and to the reaction conditions (sample weight and substrate amount). The (NH4)2.29H0.39Co0.16PMo12O40 was found to be the better catalytic system toward AA synthesis from cyclohexanone oxidation, with 40% of AA yield

Cyclohexanone Oxidation over H3PMo12O40 Heteropolyacid via Two Activation Modes Microwave Irradiation and Conventional Method

The adipic acid (AA), important precursor for Nylon production, was synthesized from cyclohexanoneoxidation by two ways, microwaves irradiation and  conventional method (under reflux) using H3PMo12O40 heteropolyacid as catalyst in the presence of hydrogen peroxide. In the order to increase the AA yield, several parameters as cyclohexanone/catalyst ratio, H2O2 concentration, solvent nature (H2O, CH3CO2H, and CH3OH, CHCl3 and CH3CN) and cyclohexanol addition to cyclohexanone were examined.  For both activation modes, the highest AA yields are of 26-28%. Whereas, with microwaves irradiation, the time gain is much more attractive 30 min compared to 20 h. Copyright © 2019 BCREC Group. All rights reserve

Supramolecular assembly of gelatin and inorganic polyanions: Fine-tuning the mechanical properties of nanocomposites by varying their composition and microstructure

A series of bionanocomposites has been synthesized through a complex coacervation process inducing the assembly of gelatin with a wide range of inorganic polyanions (IPyAs) differing by their diameter and charge and including polyoxometalates (POMs) and a polythiomolybdate cluster. The microstructure and stoichiometry of these hybrid coacervates, which are strongly dependent on the charge matching between both components, have been studied by combining Fourier transform infrared (FT-IR) spectroscopy, solid-state nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), elemental analysis, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) elemental mapping. The mechanical properties of these materials were deeply characterized by tensile measurements at large deformation, revealing different behaviors (i.e., elastomer and ductile), depending on the nature of the IPyA. It is noteworthy that the mechanical properties of these bionanocomposites are strongly enhanced, compared to pure gelatin hydrogels. When attempting to connect structure and properties in these bionanocomposites, we have demonstrated that the density of cross-links (gelatin triple helices and IPyA) is the key parameter to control the extensibility of these materials

Designing functional polyoxometalate-based ionic liquid crystals and ionic liquids

International audiencePolyoxometalate (POM) compounds constitute a wide family rich of more than several thousand inorganic compounds which can be finely tuned at the molecular level. Considering their high diversities in structures and properties, the incorporation of such inorganic components into liquid crystalline phases or ionic liquid phases is particularly relevant for the elaboration of functional materials. By adjusting the molecular structures of the anions and the nature of the counter cations, many authors designed different types of mesophases sometimes with application in optoelectronics, or true POM-based Ionic liquids (POM-ILs with melting temperature below 100 °C). The latter turn out to be highly interesting for various applications in catalysis, depollution, or protection of the historical heritage. This review focuses on the recent developments in these organic/inorganic hybrid materials, POMbased Ionic liquid crystal and POM-ILs and their applications

Improvement of the Hydrolytic Stability of the Keggin Molybdo- and Tungsto-Phosphate Anions by Cyclodextrins

International audienceKeggin-type molybdo- and tungsto-phosphate polyoxoanions are among the most popular polyoxometalates (POMs) but suffer from their limited stability at low pH in aqueous solution. Their superchaotropic properties generate strong supramolecular complexes with cyclodextrins (CDs), which significantly affect the hydrolytic stability of POM. This chaotropically driven stabilization effect was systematically monitored by 31P NMR spectroscopy covering a wide range of pH (from 0 to 8) and varying the nature of the CD (α-, β-, and γ-form). A shift of ca. two pH units of the stability domains of these POMs was found in the presence of two equivalents of γ-CD compared to pure water, leading to keep intact the PW12O403-anion without any decomposition up to pH 3.5 (versus 1.5 in pure water) and pH 2.5 for PMo12O403-, which begins to decompose even at pH 0 in pure water. The effect of the smaller CDs (α- and β-form) is much less pronounced (only 0.5 pH units shift of the stability domain) confirming the importance of host-guest size matching to form a sandwich-type inclusion complex and thus protect the POM structure against basic hydrolysis. Such complexation was further supported by 183W and 1H NMR spectroscopy. Finally, using quantitative 31P NMR analyses, the new speciation and formation constants of phospho-molybdates and phospho-tungstates in the presence of cyclodextrins are determined and compared to those previously reported in pure water or in the 50:50 water/1,4-dioxane mixture

MIL-101(Cr) MOF as a Support for Reactive Polyoxometalates (POMs) Clusters. Principles of POMs Encapsulation and Chemistry of POMs Inside MIL-101 Cavities

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The primary stages of polyoxomolybdate catalyzed cyclohexanone oxidation by hydrogen peroxide as investigated by in situ NMR. Substrate activation and evolution of the working catalyst

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