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Sodium dithionite

Sodium dithionite
Sodium dithionite
Sodium-dithionite-xtal-1992-3D-balls.png
Sample of sodium dithionite.jpg
Names
Other names
D-Ox
Hydrolin
Reductone
Sodium hydrosulfite
Sodium sulfoxylate
Sulfoxylate
Vatrolite
Virtex L
Identifiers
3D model (Jmol)
ChEBI
ECHA InfoCard 100.028.991
EC Number 231-890-0
PubChem CID
RTECS number JP2100000
UN number 1384
Properties
Na2S2O4
Molar mass 174.107 g/mol (anhydrous)
210.146 g/mol (dihydrate)
Appearance white to grayish crystalline powder
light-lemon colored flakes
Odor faint sulfur odor
Density 2.38 g/cm3 (anhydrous)
1.58 g/cm3 (dihydrate)
Melting point 52 °C (126 °F; 325 K)
Boiling point Decomposes
18.2 g/100 mL (anhydrous, 20 °C)
21.9 g/100 mL (Dihydrate, 20 °C)
Solubility slightly soluble in alcohol
Hazards
Harmful (Xn)
R-phrases R7, R22, R31
S-phrases (S2), S7/8, S26, S28, S43
NFPA 704
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g., gasoline) Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point 100 °C (212 °F; 373 K)
200 °C (392 °F; 473 K)
Related compounds
Other anions
Sodium sulfite
Sodium sulfate
Related compounds
 Sodium thiosulfate
Sodium bisulfite
Sodium metabisulfite
Sodium bisulfate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Sodium dithionite (also known as sodium hydrosulfite) is a white crystalline powder with a weak sulfurous odor. It is the sodium salt of dithionous acid. Although it is stable under most conditions, it will decompose in hot water and in acid solutions. It can be obtained from sodium bisulfite by the following reaction:

Raman spectroscopy and single-crystal X-ray diffraction studies of sodium dithionite in the solid state reveal that sodium dithionite exists in different forms. In one anhydrous form, the dithionite ion has C
2 geometry, almost eclipsed with a 16° O-S-S-O torsional angle. In the dihydrated form (Na
2S
2O
4.2H
2O), the dithionite anion has a shorter S-S bond length and a gauche 56° O-S-S-O torsional angle.

The weak S-S bond causes the dithionite anion to dissociate into the [SO2]− radical anion in aqueous solution, which has been confirmed by ESR spectroscopy. It is also observed that 35S undergoes rapid exchange between S2O42− and SO2 in neutral or acidic solution, consistent with the weak S-S bond in the anion.

Sodium dithionite is stable when dry, but is slowly oxidized by air when in solution. Even with the absence of air, solutions of sodium dithionite deteriorate due to the following reaction:


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