Sodium Sulphoxylate, Na₂SO₂

Sodium Sulphoxylate, Na₂SO₂, maybe obtained by the action of sulphur sesquioxide on sodium ethoxide; on the addition of sulphuric acid to the mixture, sodium ethylsulphoxylate, Na.C₂H₅.SO₂, is first formed, which, when kept overnight, undergoes hydrolysis. The solution, acidified with more dilute sulphuric acid, then yields the required sodium salt as a white precipitate which may be separated and dried over phosphorus pentoxide. The salt is fairly stable and may be heated to 110° C. without change; on exposure to air, however, it turns yellowish-brown. It is readily soluble in hot water, unattacked by hot mineral acids, but decomposed by a hot mixture of fuming nitric acid and bromine.

The hydrosulphites, M₂S₂O₄, may be regarded as derived simultaneously from sulphoxylic and sulphurous acids, having the constitution , where M represents an alkali metal.

The sulphates and persulphates are all derived from sexavalent sulphur, and the sulphites also appear to belong to the same class, although, as already mentioned, the possibility of quadrivalent sulphur is not precluded.

The difference in stability of inorganic substances containing sulphur in varying degrees of valency is reflected in the relative readiness with which they undergo spontaneous oxidation. By treating solutions of such substances with ozonised oxygen, the order in which oxidation occurs has been shown to be: