Sodium tungstate

Chemical properties

Sodium tungstate is a sodium salt of orthotungstate. It is a colorless crystals or white crystalline powder. Soluble in water; insoluble in alcohol and acids. noncombustible. Sodium tungstate has three crystalline forms, δ, γ and β. The transition temperature from δ to γ is about 570℃, and from γ to β is about 585℃. In hydrogen is heated to 700 ℃ also does not change, to 1100 ℃ will become metal tungsten.

The Uses of Sodium tungstate

Intermediate in preparation of tungsten compounds, (e.g., phosphotungstate), reagent, fire-proofing fabrics and cellulose, alkaloid precipitant.

Synthesis

A mixture of the SM (1.7 g, 3.3 mmol), AcOH (15 mL), Na2WO4 (209 mg, 0.60 mmol), H2O2 (50%, 2.3  mL, 6.6 mmol) was stirred at RT overnight. The solvent was removed in vacuo and ice/H2O  was added to the residue. The mixture was extracted with DCM. The combined  organics were dried, concentrated, and purified by silica gel chromatography to  provide sodium tungstate. [1.65 g, 90%]

Definition

ChEBI: Sodium tungstate is an inorganic sodium salt having tungstate as the counterion. Combines with hydrogen peroxide for the oxidation of secondary amines to nitrones. It has a role as a reagent. It contains a tungstate.

Preparation

Sodium tungstate is obtained by digestion of tungsten ores, the economically important representatives of which are tungstates, in base. Illustrative is the extraction of sodium tungstate from wolframite:
Fe/MnWO4 + 2 NaOH + 2 H2O → Na2WO4?2H2O + Fe/Mn(OH)2
Sodium tungstate can also be produced by treating tungsten carbide with a mixture of sodium nitrate and sodium hydroxide in a fusion process which overcomes the high exothermicity of the reaction involved.

Flammability and Explosibility

Not classified

Safety Profile

Poison by ingestion, intravenous, intramuscular, and subcutaneous routes. Experimental reproductive effects. Mutation data reported. When heated to decomposition it emits toxic fumes of Na2O. See also TUNGSTEN COMPOUNDS.