Peroxodisulphuric acid

Peroxodisulphuric acid, H2S2O8, is a strong acid whose second pK is below zero (Kolthoff and Miller ). Under the conditions normally employed in peroxodisulphate oxidations (aqueous solution, pH >1) the ion 8208 is the dominant species. The ion is a powerful two-electron oxidising agent with a redox potential of — 2.01 V. In the majority of its reactions the primary step is the formation of sulphate radical-ions, either by spontaneous fission of the peroxide bond, or by attack on a substrate X, i.e. 

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