Peroxotungstates

One problem associated with the peroxotungstate-catalyzed epoxidation system described above is the separation of the catalyst after the completed reaction. To overcome this obstacle, efforts to prepare heterogeneous tungstate catalysts have been conducted. De Vos and coworkers employed W catalysts derived from sodium tungstate and layered double hydroxides (LDH - coprecipitated MgCU, AICI3, and NaOH) for the epoxidation of simple olefins and allyl alcohols with... 

The highly chemo-, regio-, and diastereoselective and stereospecific epoxidation of various allylic alcohols with only 1 equivalent of hydrogen peroxide in water solvent could be efficiently catalyzed by an isolated dinuclear peroxotungstate [W203(02)4(H20)2]2 [93,94] ... 

Figure 13.12 Covalent binding of peroxotungstate species with phosphorylated spacers.

The peroxotungstate [W203(02)4(H20)2], immobilized on dihydroimidazolium-based ionic liquid-modifed Si02 has been employed for alkene and allylic alcohol epoxidation... 

Figure 12. Schematic representation of the active peroxotungstate catalyst covalently anchored to silica via phosphoramide group [136].

Over the years it has been shown that complexes prepared from organophosphorous ligands in combination with peroxotungstic acid or its quaternary ammonium salts exhibit efficient catalytic properties. In order to make an efficient recycling of the catalyst possible and get tungsten-free products and effluents, some of these catalysts were immobilized onto polystyrene, poly benzimidazole and polymethacrylate copolymers modified by the introduction of the phosphorous(V)-containing ligands. 

Chromium compounds are covered above. Most tetraperoxomolybdates(2-) and tetra-peroxotungstates(2-) explode when heated or struck [1], An acetate bridged bis-diperoxomolybdate(VI) exploded when heated [3], Organoperoxoniobium compounds occasionally explode on exposure to air [2], A peroxovanadate complex is reported seriously explosive. 

Gelbard has used peroxotungstates supported on polypyridine polymers in the epoxidation of cyclohexene with hydrogen peroxide.66 Polypyridine polymers were also used to support heteropolyperoxometallates for use in the oxidation of alcohols with hydrogen peroxide.67 The tetranuclear complex [cetylpyridinium chloride][P04 WO(02)2 4] supported on polypyridine was found to be an effective catalyst for the oxidation of cyclohexanol to cyclohexanone, also with hydrogen peroxide. 

Sulfoxide is shown to be the oxygen donor mechanism and kinetics given Peroxotungstate intermediates 35 °C mixed-addenda... 

PR Peroxotungstic acid forms when WO3 is reacted with hydrogen peroxide. 

Peroxotungstic acid is also generated when tungsten powder is dissolved in hydrogen peroxide. 

Reaction of tungstates with hydrogen peroxide yields in peroxotungstates. 

WO52- [W03(02)]2- By neutralization of peroxotungstic acid solutions increase... 

Peroxotungstic acids like H2WO6 or H2W2O11 can be exhacted from nitrate solutions into trialkyl-(C7-C9)-benzyl ammonium nitrate dissolved in trichloroethe-lyne. 

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