Peroxosulfuric acids, H₂S₂O₈ and H₂SO₅

  The reaction between cold, anhydrous H₂O₂ and chlorosulfonic acid yields peroxomonosulfuric acid, H₂SO₅, and peroxodisulfuric acid, H₂S₂O₈ (scheme 1.1). Conversion of H₂S₂O₈ (Table 15.8) to H₂SO₅ (1.1) occurs by controlled hydrolysis.

(1.1)

                                            (1.1)

   Both acids are crystalline solids at 298 K. Few salts of H₂SO₅ are known, but those of H₂S₂O₈ are easily made by anodic oxidation of the corresponding sulfates in acidic solution at low temperatures and high current densities. Peroxodisulfates are strong oxidizing agents (equation 1.2), and oxidations are often catalysed by Ag‏, with Ag(II) species being formed as intermediates. In acidic olutions, [S₂O₈]^2-  oxidizes Mn^2‏+ to [MnO₄]^- , and Cr³⁺‏ to [Cr₂O₇]^2- .

               (1.2)

   Peroxodisulfuric acid smells of ozone, and when K₂S₂O₈ is heated, a mixture of O₂ and O₃ is produced.