Tungsten reagent, oxidation with

Typically, 38 g. (0.1 mole) of dichromium tungsten(VI) oxide and 18.7 g. (0.3 mole) of oven-dried, reagent-grade, magnesium fluoride are mixed and placed in a platinum crucible fitted with a cover. 

The new tungsten reagents (1-Vl) are also effective for deoxygenation of epoxides to the parent olefin. Reagents V and Vl are the cheapest and most convenient reagents for this purpose however, reagents l-lll serve well for small- and medium-scale reactions. In a typical experiment WCl (0.15 mole) is added to THF (420 ml.) cooled to —62° n-butyllithium (0..30 mole) is added slowly at this temperature. The mixture is allowed to warm slowly to room temperature. The oxide (0.08 mole) is added. A rapid exothermic reduction takes place. After 0.5 hr. the product is poured into an aqueous solution containing sodium tartrate and NaOH. and the olefin extracted with hexane. 

Dithiol is a less selective reagent than thiocyanate for molybdenum. Tungsten interferes most seriously but does not do so in the presence of tartaric acid or citric acid (see Section 17.34). Tin does not interfere if the absorbance is read at 680 nm. Strong oxidants oxidise the reagent iron(III) salts should be reduced with potassium iodide solution and the liberated iodine removed with thiosulphate. 

For a number of years, phenolic substances were dosed by colorimetric techniques, based on redox reactions usually known as Folin Ciocalteau methods, even if a number of adjustments were developed to fit different matrix characteristics. The Folin Cioalteau reagent is a mixture of phosphomolybdic and phosphotingstic acids, with molybdenum in the 6+ oxidation state and, when the reaction takes place, it is reduced to form a complex called molybdenum blue and tungsten blue. In this complex, the mean oxidation state is between 5 and 6 and the formed complex is blue so it can be read spectrophotometrically at 750 nm. 

Anti hydroxylation of an alkene is readily achieved with peroxycarboxylic adds. Add-catalyzed ring opening of the irutial produd, an oxirane (epoxide), forms the monoester of a 1,2-diol, hydrolysis of which affords the parent diol. Alternative reagents whi ate often used for anti hydroxylation of alkenes are hydrogen peroxide with oxides of tungsten > 4.2i gj. selenium, 444i and iodine-silver benzoate (Pr6vost reaction).. ... 

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