R. I. Maksimovskaya

Role of protons in methyl phenyl sulfide oxidation with hydrogen peroxide catalyzed by Ti(IV)-monosubstituted heteropolytungstates

Acid tetrabutylammonium salts of Ti(IV)-monosubstituted heteropolytungstate, PW11TiO405−, show high catalytic acitivity in the oxidation of methyl phenyl sulfide with hydrogen peroxide, while the corresponding tetrabutylammonium salts containing no protons are poor catalysts for this reaction.

Titanium-Substituted Heteropolytungstates as Model Catalysts for Studying the Mechanisms of Selective Oxidation by Hydrogen Peroxide

The 31P NMR method shows that four forms of titanium(IV)-monosubstituted Keggin-type heteropolytungstate (Ti–HPA) exist in MeCN: the dimer (Bu4N)7[{PTiW11O39}2OH] (in the abbreviated form, (PW11Ti)2OH or H1), its conjugate base (PW11Ti)2O (1), and two monomers, PW11TiO (2) and PW11TiOH (H2). The ratio between the forms depends on the concentrations of H+and H2O. Dimer H1is produced from 2in MeCN when H+(1.5 mol) is added, and monomer H2is the key intermediate in this process. The catalytic activity of Ti–HPA in the oxidation of thioethers by H2O2correlates with their activity in peroxo complex formation and decreases in the order H2> H1> 2. The reaction of 2with H2O2in MeCN occurs slowly to form the inactive peroxo complex PW11TiO2(A). The addition of H2O2to H1and H2most likely results in the formation of the active hydroperoxo complex PW11TiOOH (B). Complexes Aand Btransform into each other when H+or OH–(1 mol) is added per 1 mol of Aor B, respectively. The activity of Btoward thioethers in the stoichiometric reaction is proven by 31PNMR and optical spectroscopy.

Scientific bases for the synthesis of highly dispersed framework zirconium phosphate catalysts for paraffin isomerization and selective oxidation

Results of the systematic study of the synthesis of highly dispersed framework zirconium phosphates stabilized by ammonium, lanthanum, aluminum, manganese, and cobalt cations are summarized. The synthesis involves the mechanochemical activation of a mixture of solid reactants (salts) or the sol–gel process each followed by the hydrothermal treatment (HTT) of obtained precursors in the presence of surfactants. The genesis of dispersed systems under investigation is studied by modern physical methods providing information on the state of the bulk and surface of the systems. It is found that the local structure of sol nanoparticles and zirconium phosphate crystalline nuclei arising from mechanochemical activation products depends on the nature of initial substances. This, in its turn, makes different crystallization mechanisms possible during the HTT process: the dissolution/precipitation mechanism or the mechanism of oriented mating of primary particles. The crystallization mechanism in HTT and the reaction system composition influence the nature of resulting complex zirconium phosphate phases, their thermal stability, dispersity, and porous structure parameters. The relationship between the bulk structure parameters of framework zirconium phosphates, which are controlled by varying the chemical composition and conditions of synthesis, and the surface characteristics of the systems (the strength and concentration of different Lewis and Br@nsted sites) is studied. It is shown that systems based on framework zirconium phosphates are promising catalysts for paraffin (pentane and hexane) isomerization, the selective oxidation of methane by oxygen into synthesis gas at short contact times, and the oxidative dehydrogenation of propane into propylene.

Oxidation of methyl phenyl sulfide with hydrogen peroxide catalyzed by Ti(IV)-substituted heteropolytungstate

Alkylammonium salts of Ti(IV)-substituted heteropolytungstate, PW11TiO105−, catalyze the oxidation of methyl phenyl sulfide with hydrogen peroxide. The yield of the corresponding sulfoxide and sulfone is practically quantitative. A31P NMR study confirms the formation and reactivity of the PW11O39TiO25− peroxo complex in organic media.

Tetrapalladium-Containing Polyoxotungstate [PdII4(α-P2W15O56)2]16–: A Comparative Study

The novel tetrapalladium(II)-containing polyoxometalate [Pd(II)4(α-P2W15O56)2](16-) has been prepared in aqueous medium and characterized as its hydrated sodium salt Na16[Pd4(α-P2W15O56)2]·71H2O by single-crystal XRD, elemental analysis, IR, Raman, multinuclear NMR, and UV-vis spectroscopy. The complex exists in anti and syn conformations, which form in a 2:1 ratio, and possesses unique structural characteristics in comparison with known {M4(P2W15)2} species. (31)P and (183)W NMR spectroscopy are consistent with the long-term stability of the both isomers in aqueous solutions.

Catalytic properties of heteropoly compounds in 1,3-butadiene oxidation with hydrogen peroxide

The homogeneous oxidation of 1,3-butadiene (BD) in H2O2-HPC-CH3CN (HPC = heteropoly compound) solutions has been investigated. The route of the reaction depends on the nature of the metal capable of coordinating with active oxygen in the HPC. The products of radical BD oxidation (acrolein, 3-butene-1,2-diol, 2-butene-1,4-diol, furan) form in the presence of H3+nPMo12 − nVnO40 (n = 1, 2) acids. 3,4-Epoxy-1-butene (EB) and acrolein + furan, which form in equal amounts in the presence of the (n-Bu4N)5PW11O39Fe(OH) salt, result, respectively, from the electrophilic addition of hydrogen peroxide to BD and from radical BD oxidation on iron-oxygen complexes in the HPC composition. The reaction carried out in the presence of (n-Bu4N)3{PO4[WO(O2)2]4}, (n-Bu4N)5Na0.6H1.4PW11O39, or (EMIm)5NaHPW11O39 yields EB with high selectivity on the reacted BD basis (up to 97%) and H2O2 (about 100%). The formation and conversion of the phosphotungstate peroxo complexes PWnOmα−(n = 2, 3, 4) that are active in BD epoxidation have been investigated by 31PNMR spectroscopy. The role of the tetrabutylammonium and ethylmethylimidazolium cations in the formation of these complexes has been demonstrated.

Thermal transformations of α-H6P2Mo18O62·nH2O heteropolyacid

According to the 31P NMR spectroscopy, heteropolyacid (HPA) H6P2Mo18O62·nH2O (P2Mo18), α-isomer of the Dawson structure, transforms upon heating above 80 °C partially (up to 30%) to γ-isomer, in which both polar groups Mo3O13 of the heteropolyanion are turned by 60° around the N3 axis, and partially to β-isomer in which only one group is turned. The β- and γ-isomers of P2Mo18 have been found for the first time. Their transformation into the α-isomer occurs upon rehydration in one week in air and in 1 h in an aqueous solution. HPA P2Mo18 decomposes on heating up to 350 °C to HPA H3PMo12O40 (PMo12) and a previously unknown phase of the HPMo6I21 composition, which in its turn decomposes at ∼375 °C to molybdenyl phosphates and IiI3. The PMo12 decomposition occurs via two routes to form the same products at temperatures of ∼400 and 450 °C with corresponding exotherms of IiI3 crystallization.

Oxidative ammonolysis of methylpyrazine over binary catalytic systems: III. Phosphorus-molybdenum system: Catalytic properties and the active component

The phase composition of the binary phosphorus-molybdenum system with a Mo/P ratio of 3-24.5 and its catalytic properties in the reaction of oxidative ammonolysis of methylpyrazine are studied. X-ray amorphous phases of molybdenyl phosphate and phosphorus modified molybdenum trioxide are active in the formation of pyrazinonitrilee.

Acidity of heteropoly acids with various structures and compositions studied by IR spectroscopy of the pyridinium salts

The acidity on the “proton affinity” scale was determined by IR spectroscopy of the pyridinium salts for nineteen heteropoly acids of nine structural types (including two with the previously unknown structure) and one isopoly acid. All heteropoly acids exhibited a high acidity at the level of CF3SO3H and HClO4. H3PW12O40 was the strongest acid.

Study of the P2O5−MoO3 system in acrolein oxidation

Catalytic properties of the binary phosphorus-molybdenum system with Mo/P=3–24.5 in acrolein oxidation have been studied. The selectivity to acrylic acid and carbon oxides practically does not depend on the chemical composition of the system, and the maximum activity is observed for Mo/P=12. The catalytic properties of the system are determined by an X-ray amorphous phase, apparently molybdenyl phosphate.