Sodium tungstate, reaction with

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). 

The sodium tungstate solution is filtered from the resulting slurry. Similarly, in the alkaH roasting process, the concentrate, either scheeHte or wolframite, is heated with sodium carbonate in a rotary kiln at 800°C and then leached using hot water to remove the sodium tungstate. Wolframite ores are also decomposed by reaction with a sodium hydroxide solution at 100°C. 

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... 

In aqueous solutions, calcium chloride undergoes double decomposition reactions with a number of soluble salts of other metals to form precipitates of insoluble calcium salts. For example, mixing solutions of calcium chloride with sodium carbonate, sodium tungstate and sodium molybdate solutions precipitates the carbonates, tungstates, and molybdates of calcium, respectively. Similar precipitation reactions occur with carboxylic acids or their soluble salt solutions. CaCb forms calcium sulfide when H2S is passed through its solution. Reaction with sodium borohydride produces calcium borohydride, Ca(BH4)2. It forms several complexes with ammonia. The products may have compositions CaCl2 2NH3, CaCb dNHs, and CaCb SNHs. 

The Falin-Ciocalteu reagent (FCR) is a complex formed in a reaction between sodium tungstate and sodium molybdenate in hydrochloric add and phosphoric acid, which turns yellow after lithium sulphate is added. The reagent reads in an alkaline environment with reducing compounds. Such a reaction gives a blue chromophore which is observed by colorimetry. The Folin-Ciocalteu method is highly sensitive - both to phenolic and non-phenolic compounds, e.g. proteins, vitamin C, vitamin Bj, folic acid, Cu(I). The method is applied most frequently to determine the total content of phenolic compounds [34,35]. If that is the case, a sample for determination should be prepared in a proper manner to minimise the effect of non-phenolic... 

According to C. F. Barwald and A. Monheim (1835), the decomposition is accelerated by the presence of organic substances. J. Milbauer tried the effect of thirty-two metal chlorides of sodium tungstate and molybdate of uranyl sulphate and of sulphuric, selenic, arsenic, and boric acids on the photo-decomposition of chlorine water, and found. that none accelerated but that most retarded the action. Chlorine catalyzes the decomposition of bromine water and bromine, chlorine water while iodine does not accelerate, but rather retards the reaction, probably by forming relatively stable iodine compounds. A. Bcnrath and H. Tuchel found the temp, coeff. of the velocity of the reaction with chlorine water between 5° and 30° increases in the ratio 1 1 395 per 10°. 

Reduction of MoIybdenum(VI) and Tungsten VI) Compounds. Pour 3 ml of an ammonium molybdate solution into each of four test tubes, acidify with a 2 N hydrochloric acid solution, and heat up to boiling. Add solutions of sulphuric acid, hydrogen sulphide, and tin(Il) chloride to three of the tubes, respectively, and throw one or two small pieces of zinc into the last tube. Perform similar experiments using sodium tungstate as the initial reactant. Write the equations of the reactions. 

Molybdenum and Tungsten Peroxide Compounds. Pour ammonium molybdate and sodium tungstate solutions into separate test tubes, acidify them with sulphuric acid, and add several drops of a 1 % hydrogen peroxide solution to each tube. How does the colour of the solutions change Write the equations of the reactions. 

In a typical solvent-extraction process,211 the pH value of the sodium tungstate solution is adjusted to about 2.5 with sulfuric acid, and the tungsten is extracted into a 7% solution of the tertiary amine Alamine 336 plus 7% isodecanol in kerosene in two countercurrent stages at a temperature of 50 °C. Distribution data are consistent with the extraction of species such as H2W1204o6 and Wi2O408- in reactions of the type208-212... 

A. r>itr>o80-tert-oetane To a 1-L, three-necked flask equipped with an addition funnel, a mechanical stirrer, and a thermometer are added 120 ml of methanol, 51.7 g of tert-octylamine (0.4 mol) and 90 mL of water containing 1.2 g (0. 0028 mol) of the tetrasodium salt of ethylenediaminetetraacetic acid and 2.52 g (0. 0076 mol) of sodium tungstate dihydrate. The solution is cooled to 15°C in an ice bath and hydrogen peroxide (361 mL of a 16% solution, 1.7 mol) (Notes 1 and 2) is added over 5 hr. The blue reaction mixture is stirred for an additional 16 hr and the product is extracted with petroleum ether (3 x 50 mL). Unreacted amine is removed by washing twice with 2 N hydrochloric acid. After the blue organic layer is washed with brine, it is dried over MgS04. Petroleum ether is removed by distillation at atmospheric pressure. Continued distillation of the product affords 29.7 g of nitroso-tert-octane... 

A delicate reaction for ferrous iron consists in adding a solution of sodium phospho-tungstate, acidified with hydrochloric acid, to the solution suspected of containing a ferrous salt. The whole is rendered alkaline with caustic soda, when a blue coloration is produced if a ferrous salt is present.8 This reaction is more delicate than that with potassium ferricyanide. 

The observed stereochemistry of addition suggests that oxiranes (epoxides) may be intermediates. Oxiranes may, indeed, be isolated from the reaction of certain alkenes with hydrogen peroxide in the presence of sodium tungstate. °... 

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