Peroxo-tungstate

However, particularly for the unsaturated acids, the epoxidation catalysis was not heterogeneous. Competitive anion exchange between the (peroxo)-tungstate and the carboxylate possibly causes leakage of W. 

Related peroxo-tungstates and -molybdates (Pli2P02)(M0(02)2]2 (M = W or Mo) were studied as catalysts for H2O2 oxidation of sulfoxides. The selectivity for sulfoxide was low for these catalysts [18]. 

In contrast to the preceding reagents, oxidation with H202 catalyzed by molybdate and tungstate salts or Hg(OAc)2,722,723 and the Hg(OAc)2-promoted oxidation with a molybdenum peroxo complex724 can be applied to transform acetylene and terminal acetylenes to glyoxal and a-ketoaldehydes, respectively, in fair to good yields. 

As with percarboxylic acids, hydrogen peroxide usually requires metal activation.151-154 Peroxo complexes of d° transition metals can often be used to cleave olefins. Tungstic acid cleaves olefins to the carboxylic acid using 35% m/m hydrogen peroxide.154 Sodium tungstate has also been reported to... 

It is possible to speed up aliphatic tertiary amine oxidation by adding tungstate or molybdate catalysts.334 However, for oxidation of aromatic and particularly heterocyclic tertiary nitrogen, a stronger system than hydrogen peroxide alone is required. iV-Oxidation of heterocycles is of pivotal importance in industrial chemical synthesis.335 Catalysed systems have been applied and these are dominated by metal peroxo systems based on molybdenum or tungsten. For example, quinoxaline and pyrazine may be oxidized to mono- or... 

Peroxo derivatives of polymolybdates and polytungstates were reviewed in 1994.375 The solution chemistry of isopolyoxo(peroxo)molybdates and -tungstates has recently been investigated by 170... 

In general, the presence of hydrogen peroxide prevents the polycondensation tendency of the tungstate ions. All peroxo tungsten compounds are unstable. The degree of instability increases with increasing W 02 ratio. The 1 4 compound even may explode. 

Single-crystal X-ray structures are available for the enzymes isolated from A nodosum (holoenzyme),[ " l Cur. inaequalis (apoenzyme and tungstate variant,sulfate variant, azide form of the holoenzymel and the native holoenzyme plus its peroxo formP ]), Cor. officinalis (phosphate variant) and Cor. pilulifera (phosphate variant). The Cor. pilulifera peroxidase also contains a structural Ca + ion. The enzymes from the red algae are hexamers of dimers with 595 amino acids per monomeric subunit, the... 

The preparations and properties of several peroxo-molybdate and -tungstate complexes have been investigated, the compounds reported include K2W08 and hydrated salts of the [MO ] (M = Mo or W n = 5—8) anions with the cations Na", Sc ", or Mo peroxo-complexes have been used to... 

A plausible mechanism for the triple catalytic H2O2 oxidation with osmium-tungsten oxides is depicted in Scheme 5.13. The peroxo species generated from tungstate and H2O2 rapidly recycles the NMM to NMO, which in turn reoxidizes Os(Vl) to Os(Vlll). 

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