Sodium pentathionate, Na₂S₅O₆

Sodium pentathionate has not been obtained in the pure state, but is said to be one of the products of the decomposition of acid solutions of sodium thiosulphate, the sulphur dioxide liberated reacting with the thiosulphate:

5Na₂S₂O₃ + 3SO₂=2Na₂S₂O₆ + 3Na₂SO₃.

It is also said to react with sodium sulphite, yielding the trithionate and thiosulphate:

Na₂S₅O₆+2Na₂SO₃=Na₂S₃O₆+2Na₂S₂O₃.