Dithionates

Structure of the dithionate anion

Dithionates (outdated also hypodisulfates ) are the inorganic salts of the unstable dithionic acid (disulfuric acid, H ₂ S ₂ O ₆ ) and weak oxidizing agents . The salts consist of a dithionate ion S ₂ O ₆ ²⁻ , which is present as a dianion in an acidic environment (H ⁺ excess) , and a metal cation. The dithionate anion has a tetrahedral arrangement on both sulfur atoms and is sterically comparable to ethane . There is also a staggered and an ecliptic conformation here ; In the hydrate of sodium dithionate Na ₂ S ₂ O ₆ · 2H ₂ O, the arrangement is staggered, while the anhydrous salt has an ecliptic structure.

presentation

The pure dithionic acid can only be represented in a dilute aqueous solution:

${\displaystyle {\ce {BaS2O6 + H2SO4 -> H2S2O6 + BaSO4}}}$

The solution obtained in this way still has to be separated from the barium sulfate and can then be concentrated at room temperature over phosphorus pentoxide to a density of 1.347 g · cm ⁻³ . Higher concentration leads to the decomposition of the contained dithionic acid.

Dithionates are normally not formed directly from the dithionic acid, but with the help of a more stable acid. The dithionic acid serves here only as a name stem. The formation of manganese (II) dithionate from manganese dioxide and sulphurous acid (schematic) can be cited as an example:

${\displaystyle \mathrm {\ MnO_{2}\ +\ 2\ SO_{2}\rightarrow \ MnS_{2}O_{6}} }$

Dithionates can also be produced by anodic oxidation of hydrogen sulfates .

stability

Like dithionic acid, the dithionates disproportionate easily into SO ₂ and SO ₄ ²⁻ when heated or acidified .

For example, potassium dithionate breaks down at 258 ° C into potassium sulfate and sulfur dioxide.

${\displaystyle \mathrm {K_{2}S_{2}O_{6}\rightarrow \ K_{2}SO_{4}\ +\ SO_{2}} }$

Individual evidence

1. ^ ^{A b c} A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 91st – 100th, improved and greatly expanded edition. Walter de Gruyter, Berlin 1985, ISBN 3-11-007511-3 , p. 519.
2. ↑ Greenwood, NN; Earnshaw, A. (1997). Chemistry of the Elements, 2nd Edition , Oxford: Butterworth-Heinemann, ISBN 0-7506-3365-4 .
3. ↑ Georg Brauer: Dithionic acid . In: Handbook of Preparative Inorganic Chemistry . Ferdinand Enke Verlag Stuttgart, 1954, p. 305 .