Catalysts sodium tungstate

The hydrolysis of cw-epoxysuccinic acid (the initial product in the hydroxyla-tion reaction of maleic acid by hydrogen peroxide) by H2O2 is accelerated by the epoxidation catalyst sodium tungstate. The reaction is first-order within respect to the concentrations of the catalyst and the epoxide and end-product inhibition was observed. ... 

Oxidation. Maleic and fumaric acids are oxidized in aqueous solution by ozone [10028-15-6] (qv) (85). Products of the reaction include glyoxyhc acid [298-12-4], oxalic acid [144-62-7], and formic acid [64-18-6], Catalytic oxidation of aqueous maleic acid occurs with hydrogen peroxide [7722-84-1] in the presence of sodium tungstate(VI) [13472-45-2] (86) and sodium molybdate(VI) [7631-95-0] (87). Both catalyst systems avoid formation of tartaric acid [133-37-9] and produce i j -epoxysuccinic acid [16533-72-5] at pH values above 5. The reaction of maleic anhydride and hydrogen peroxide in an inert solvent (methylene chloride [75-09-2]) gives permaleic acid [4565-24-6], HOOC—CH=CH—CO H (88) which is useful in Baeyer-ViUiger reactions. Both maleate and fumarate [142-42-7] are hydroxylated to tartaric acid using an osmium tetroxide [20816-12-0]/io 2LX.e [15454-31 -6] catalyst system (89). 

Sodium tungstate is used in the manufacture of heteropolyacid color lakes, which are used in printing inks, plants, waxes, glasses, and textiles. It is also used as a fuel-ceU electrode material and in cigarette filters. Other uses include the manufacture of tungsten-based catalysts, for fireproofing of textiles, and as an analytical reagent for the deterrnination of uric acid. 

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... 

Sodium tungstate has also been used as a catalyst in the oxidation of dimethyl sulphoxide to the sulphone36. The kinetics of this reaction have been studied in great detail and it has been shown that oxygen transfer to the sulphoxide takes place via two peroxytungstic acid species (HW05 and HWOg ). 

Oxidation of secondary amines into nitrones has been extensively studied and a variety of well-known efficient oxidants and catalysts which can be employed in this process are available. Catalytic oxidation by hydrogen peroxide at room temperature is carried out by using sodium tungstate (Fig. 2.1) (28-47). 

Buonomennna, M.G., Lopea, L.C., Barbieri, G., Favia, P., d Agostino, R. and Drioli, E. (2007) Sodium tungstate immobilized on plasma-treated PVDF membranes new efficient heterogeneous catalyst for oxidation of secondary amines to nitrones. Journal of Molecular Catalysis. A, Chemical, 273, 32-38, 10.1016/... 

Hydrogen peroxide or t-butyl hydroperoxide may be used in the presence of a catalyst such as sodium tungstate(VI) or vanadyl acetylaceto-nate [ MeC0CH=C(0 )Me 2V0] for the epoxidation of allylic alcohols. The stereochemistry of the hydroxyl group has a profound effect on the stereochemistry of epoxidation. A system which has been applied to allylic alcohols, to make optically active epoxides, utilizes titanium(rV) isopropoxide, t-butyl hydroperoxide and either of the enantiomeric forms of diethyl tartrate. This system forms chiral epoxides of predictable stereochemistry. When the reactivity of epoxides is combined with the... 

Quinazoline and its derivatives 1 are converted to the corresponding quinazoline 3-oxides 3 when treated with hydroxylamine. The parent quinazoline 3-oxide is also obtained by oxidation of quinazoline with hydrogen peroxide using sodium tungstate as catalyst vide... 

A self-assembled POM [ZnWZn2(ZnW9O34)2] prepared in situ in water by mixing zinc nitrate, sodium tungstates, and nitric acid was active for the oxidation of alcohols, diols, amines, and pyridines with [94,95]. The catalyst was... 

The use of hydrogen peroxide as an oxidant is generally desirable due to cost and ease of use. Most of the development objectives could be met by removing or replacing acetic acid from the process. One of the seminal reports of the oxidation of thioethers, with hydrogen peroxide was made by Freyermuth,1 in which, sodium tungstate is used as a catalyst in the process. 

A greener method has been developed using hydrogen peroxide as the oxidant, with catalytic amounts of sodium tungstate and a quaternary ammonium phase-transfer catalyst (Equation 4.7) [16]. Since the solvent and the by-product are water, the reaction is indeed much greener (E-factor = 0.49, atom economy 67%). 

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