Halides of Sulfur and Selenium

The acids themselves have never been isolated, but salts of each have been prepared. Higher polythionates having chains of five or six sulfur atoms per molecule have been made. Tetrathionate, the most important thionic acid anion, results from the oxidation of S2OI with I2. Salts of the remaining thionic acids must be prepared by special methods. 

The sulfur-containing anion, S204, formed by the reduction of HSOj with zinc, has been called at various times hypomlfite, hydrosulfite, and dithionite. The latter name is that currently assigned to the ion, together with the structural formula O—S—S—02, An alternate structure, 

0—S—0—S—02, though perhaps more in keeping with the chemical O 

Several oxy acids of sulfur are known in addition to those mentioned in this chapter, but they are, at present, of very slight importance. 

There have been over twenty halides of sulfur and selenium reported (some only poorly characterized). Only half a dozen will be discussed in this text. It should be noted that no iodides of sulfur are known, and that the bromides of sulfur and selenium are relatively unstable. 

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