Showing papers by "Keigo Kamata published in 2013"
TL;DR: A divanadium-substituted phosphotungstate [γ-PW10O38V2(μ-OH)2− (I) could act as an efficient homogeneous catalyst for selective oxidation of sulfides with 30% aqueous H2O2 as discussed by the authors.
37 citations
TL;DR: The heterogeneous silicotungstate catalyst can be recovered by filtration and reused for the dehydration at least three times without significant loss of catalytic activity as discussed by the authors, and it can be used for the reuse of the catalytic catalysts without significant degradation.
Abstract: The heterogeneous silicotungstate catalyst can be recovered by filtration and reused for the dehydration at least three times without significant loss of catalytic activity.
30 citations
TL;DR: In this paper, the catalytic activity of a dinuclear peroxotungstate, [{WO(O2)2}2(μ-O)]2, is strongly dependent on additives, and HClO4 is the most effective.
Abstract: For the epoxidation of cyclooctene with hydrogen peroxide (H2O2), the catalytic activity of a dinuclear peroxotungstate, [{WO(O2)2}2(μ-O)]2–, is strongly dependent on additives, and HClO4 is the most effective. The reaction of [{WO(O2)2}2(μ-O)]2– with HClO4 (0.5 equiv.) gives a protonated tetranuclear peroxotungstate, [H{W2O2(O2)4(μ-O)}2]3– (I). The diastereoselectivity for epoxidation of 3-methyl-1-cyclohexene shows that steric constraints of the active site of I are comparable to those of di- and tetranuclear peroxotungstates with XO4n– ligands (X = SeVI, AsV, PV, SVI, and SiIV). The lowest XSO [XSO = (nucleophilic oxidation)/(total oxidation)] value of 0.13 for the I-catalyzed oxidation of thianthrene 5-oxide among peroxotungstates reveals that I has the most electrophilic active oxygen species. Kinetic and spectroscopic results show that an inactive species (I′) is reversibly formed by the reaction of I with water. Reaction rates for the catalytic epoxidation show first-order dependences on concentrations of alkene and I and a zero-order dependence on concentrations of H2O2. All these results indicate that oxygen transfer from I to a C=C double bond in an alkene is the rate-determining step. Computational studies support the proposed reaction mechanism.
16 citations
TL;DR: In the presence of a simple combined catalyst of a tungstate monomer (TBA2WO4, TBA: tetra-n-butylammonium) and rhodium acetate (Rh2(OAc)4), hydrosilylation of various types of substances including...
Abstract: In the presence of a simple combined catalyst of a tungstate monomer (TBA2WO4, TBA: tetra-n-butylammonium) and rhodium acetate (Rh2(OAc)4), hydrosilylation of various types of substances including ...
14 citations
TL;DR: The in situ powder XRD study showed reversible structure transformation between IVA and IVC driven by the sorption-desorption of DCE and a low-pressure hysteresis was observed probably because of hydrogen-bonding interaction between DCE molecules and polyanions.
Abstract: Three inorganic-organic-inorganic hybrids of dipalladium-substituted γ-Keggin silicodecatungstates with organic linkers of different lengths, TBA8[{(γ-H2SiW10O36Pd2)(O2C(CH2)nCO2)}2] (n = 1 (II), 3 (III), and 5 (IV), TBA = [(n-C4H9)4N]+), were synthesized by exchange of the acetate ligands in TBA4[γ-H2SiW10O36Pd2(OAc)2] (ITBA) with malonic, glutaric, and pimelic acids, respectively. The X-ray crystallographic analysis of II, IIIA (IIIA: III with DCE, DCE = 1,2-dichloroethane), and IVA (IVA: IV with 10DCE) revealed that the anion parts of II, IIIA, and IVA were inorganic-organic-inorganic hybrids composed of two dipalladium-substituted γ-Keggin silicodecatungstates connected by two dicarboxylate ligands. In the crystal structure of IVA, 10 DCE molecules per polyanion were present in the vicinity of polyanions. Compound IVB (IVB: IV with 0.2DCE) was obtained by the evacuation of IVA. The DCE sorption–desorption isotherms of IVB showed that the amount of DCE sorbed was saturated at 10.5 mol mol–1, of which t...
13 citations
TL;DR: In this article, TPA·Cl (TPA: tetra-n-propylammonium) was added to a reaction mixture of H2WO4, H2O2, and HCl and gave a novel all-inorganic mononuclear chloro oxo diperoxotungstate, TPA[WOCl(O2)2(H2O)] (I), which wa...
Abstract: Addition of TPA·Cl (TPA: tetra-n-propylammonium) to a reaction mixture of H2WO4, H2O2, and HCl gave a novel all-inorganic mononuclear chloro oxo diperoxotungstate, TPA[WOCl(O2)2(H2O)] (I), which wa...
3 citations
Patent•
12 Sep 2013
TL;DR: In this article, a method for producing a tungsten peroxide compound useful as a catalyst for the epoxidation of an alkene is described, which is characterized by comprising of reacting tungstic acid with an ammonium hydroxide compound selected from (H4N)(OH), (H3R1N) and (R1R2R3R4N) compounds.
Abstract: As a novel method for producing a tungsten peroxide compound useful as a catalyst for the epoxidation of an alkene, a method for producing a tungsten peroxide compound is provided which is characterized by comprising reacting (a) tungstic acid with (b) an ammonium hydroxide compound selected from (H4N)(OH), (H3R1N)(OH), (H2R1R2)(OH), (HR1R2R3N)(OH) and (R1R2R3R4N)(OH) Also provided is a method for producing an epoxy compound using the catalyst (In the formulae, R1 to R4 may be the same as or different from one another, independently represent a linear or branched alkyl group having 1 to 18 carbon atoms, a cycloalkyl group or a benzyl group, and may contain nitrogen or oxygen)
1 citations
TL;DR: The heterogeneous silicotungstate catalyst can be recovered by filtration and reused for the dehydration at least three times without significant loss of catalytic activity as discussed by the authors, and it can be used for the reuse of the catalytic catalysts without significant degradation.
Abstract: The heterogeneous silicotungstate catalyst can be recovered by filtration and reused for the dehydration at least three times without significant loss of catalytic activity.
1 citations