Rubidium trithionate, Rb₂S₃O₆

When rubidium persulphate reacts with somewhat more than twice the molecular proportion of strontium thiosulphate in solution, rubidium tetrathionate is formed:

Rb₂S₂O₈+2SrS₂O₃ =Rb₂S₄O₆+2SrSO₄.

The strontium sulphite produced by decomposition of the excess of strontium thiosulphate then reacts with the rubidium tetrathionate, forming trithionate:

Rb₂S₄O₆+SrS₃ = Rb₂S₃O₆+SrS₂O₃.

In presence of sulphurous acid a similar reaction takes place. The trithionate forms rhombic crystals isomorphous with those of the corresponding potassium salt, the density being 2.845.