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| Names | |
|---|---|
| IUPAC name Sodium dithionate | |
| Other names Sodium hyposulfate, Sodium metabisulfate | |
| Identifiers | |
3D model (JSmol) | |
| ChemSpider |
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| ECHA InfoCard | 100.028.682 |
| EC Number |
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| UNII | |
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| Properties | |
| Na2S2O6 | |
| Molar mass | 206.106 g/mol |
| Appearance | White crystalline powder |
| Density | 2.19 g/cm3 |
| Melting point | 190 °C (374 °F; 463 K) (decomposes) 52 °C (dihydrate) |
| Boiling point | 267 °C (513 °F; 540 K) decomposes |
| 6.27 g/100 mL (0 °C) 15.12 g/100 mL (20 °C) 64.74 g/100 mL (100 °C) | |
| Hazards | |
| NFPA 704 (fire diamond) | |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Sodium dithionate Na2S2O6 is an important compound forinorganic chemistry. It is also known under namesdisodium dithionate,sodium hyposulfate, andsodium metabisulfate. Thesulfur can be considered to be in its +5oxidation state.
It should not be confused withsodium dithionite, Na2S2O4, which is a very different compound, and is a powerful reducing agent with many uses in chemistry and biochemistry. Confusion between dithionate and dithionite is commonly encountered, even in manufacturers' catalogues.
Sodium dithionate is produced by the oxidation ofsodium bisulfite bymanganese dioxide:[1]
Alternatively, it can be prepared by the oxidation ofsodium sulfite by thesilver(I) cation:[1]
Another method is via oxidation ofsodium thiosulfate withchlorine:[citation needed]
And another method to produce sodium dithionate is treating sodium thiosulfate with sodium hypochlorite solution.
The dithionate ion represents sulfur that is oxidized relative to elemental sulfur, but not totally oxidized. Sulfur can be reduced to sulfide or totally oxidized to sulfate, with numerous intermediate oxidation states in inorganic moieties, as well as organosulfur compounds. Example inorganic ions includesulfite andthiosulfate.
Sodium dithionate crystallize asorthorhombic crystals of the dihydrate (Na
2S
2O
6). Thewater of crystallization is lost when heated to 90 °C, and the structure becomeshexagonal.[2]
Large single crystals of (Na
2S
2O
6·2H
2O) have been grown and studied for pulsed lasing purposes (pico second spectroscopy) with great success by E. Haussühl and cols.[3]
Sodium dithionate is a very stable compound which is not oxidized by permanganate, dichromate or bromine. It can be oxidized to sulfate under strongly oxidizing conditions: these include boiling for one hour with 5 M sulfuric acid with an excess of potassium dichromate, or treating with an excess of hydrogen peroxide then boiling with concentrated hydrochloric acid.
TheGibbs free energy change for (for example) the dithionate anion's oxidation to sulfate is a negative −300 kJ/mol, making it thermodynamically unstable against oxidation, but the kinetics for this reaction are rather poor. For similar reasons, the dithionate anion has been used to form single crystals of large cation complexes in high oxidation states, as the resulting salts are very likely highly kinetically stable(unless in extraordinary conditions that obviously do not belong to crystal analysis- see above), enough to survive all the way throughout the analysis of the crystal.
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