Sulphur Selenium Oxytetrachloride, SeSO₃Cl₄

Sulphur Selenium Oxytetrachloride, SeSO₃Cl₄ or SeCl₄.SO₃, can be produced by the direct combination of sulphur trioxide and selenium tetrachloride. It has also been obtained by heating selenium tetrachloride with chlorosulphonic acid, sulphuric acid, pyro-sulphuric acid or sulphuryl chloride,

SeCl₄ + Cl.SO₂OH = SeCl₄.SO₃ + HCl,

also by the action of pyrosulphuryl chloride on selenium, and by heating a mixture of sulphuryl and selenyl chlorides at 170° to 180° C. in a sealed tube:

SO₂Cl₂ + SeOCl₂ = SeSO₃Cl₄.

The product of these reactions is a fairly stable colourless crystalline solid which melts at 165° C. and boils at 185° C. When vaporised it is largely dissociated, the vapour density at 210° C. being approximately one-third of the theoretical.

Water decomposes the substance with the formation of selenious, sulphuric and hydrochloric acids.

The constitution of the substance has been represented by the formula



but Prandtl and Borinski consider that it is better represented as a simple additive compound, SeCl₄.SO₃.