Sodium tetrathionate
Sodium tetrathionate is a salt of sodium and tetrathionate with the formula Na2S4O6.H2O. The salt normally is obtained as the dihydrate. It is a colorless, water-soluble solid. It is one member of the polythionates, which have the formula 2-. Other members include trithionite, pentathionate, hexathionate.
Sodium tetrathionate is formed by the oxidation of sodium thiosulfate, e.g. by the action of iodine:.
The reaction is signaled by the decoloration of iodine. This reaction is the basis of iodometric titrations.
Other methods include the coupling of sodium bisulfite with disulfur dichloride:
The ion has idealizes C2 symmetry, like H2S2. The S-S-S dihedral angle is nearly 90 °. The central S-S distance is 2.115 Å, 0.01 Å longer than the two other S-S distances as well as those distances in most polysulfanes.
