Sodium Tungstate Dihydrate-II

2. Applications
Sodium tungstate dihydrate can be used as catalyst or as catalyst precursor in several organic reactions, namely:

a) Epoxidation
The sodium tungstate catalyzed epoxidation of α,β-unsaturated acids by hydrogen peroxide in water has been developed by Payne in 1959, and revisited by Sharpless in 1985, also in water. According to Sheldon, the epoxidation of allyl alcohol to glycidol using hydrogen peroxide and sodium tungstate was applied industrially as an alternative to thetraditional route via epichlorohydrin. The epoxidation procedure developed by Venturello and co-workers, using a Na2WO4.2H2O/H3PO4/quaternary ammonium chloride/aqueous 8% hydrogen peroxide system presents some drawbacks, since requires an excess of olefinic substrates and uses 1,2-dichloroethane, a toxic and carcinogenic chlorinated hydrocarbon solvent. In contrast, Noyori and co-workers reported a clean, halide-free, biphasic epoxidation method with 30% hydrogen peroxide in the presence of sodium tungstate dihydrate, (aminomethyl)phosphonic acid, and a phase transfer catalyst (PTC) such as Q+HSO4- (Q+ =CH3(n-C8H17)3N+) to epoxidize olefins such as cyclooctene (98% yield) or 1-dodecene (87% yield). Functionalized olefins containing an ester, ether, alcohol, or α,β-enone linkage in the same molecule can also be epoxidized by this procedure.


 

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