Persulphates Peroxodisulphates

Peroxomonosulphate and peroxodisulphate have also been used to oxidize sulphoxides to sulphones in good yields at room temperature. Potassium persulphate (KHS05) readily oxidizes a range of sulphoxides to sulphones at 0°C in yields greater than 90%, in the presence of hydroxy, keto and alkene groups82-84. The mechanism is similar to that observed for other peroxy species, as discussed above. Peroxomonosulphate oxidation has been used as an analytical procedure for the estimation of dimethyl sulphoxide84. 

Potassium persulphate solution DUute 5mL of sulphuric add (4.5mol/L reagent 1 of the phosphate determination in Section 10.2.5.4) with water to 100 mL. Add and dissolve S g of potassium peroxodisulphate, K2S20g. Store this solution at room temperature in a polyethylene bottle protected from direct sunlight. The reagent is stable for about one week. 

To 50 mL of the sample is added either 4mL of peroxodisulphate solution or 0.2 mL of sulphuric acid (reagent 1, Section 10.2.5.4) and 220 20mg of solid potassium persulphate. Dissolve the reagent by swirling. Close the bottles and place them in the autoclave, which has been filled with about 200 mL of water. Autoclave the samples for 30 min. Cool to below 50 °C and decompress the autoclave carefully, because the inner pressure of the hot sample bottles may pop the caps (if polyethylene or polypropylene bottles are used, do not decom-... 

Potassium peroxodisulphate, K2S2O8 The persulphate used in this procedure should have a low nitrogen content. Suitable reagents are from Merck (No. 1.05092 with a maximum of 0.001 % N) and BDH Analar (No. 10 218 with a maximum of 0.0005 % NH3). Both reagents have been tested and found to contain ca. 0.00045 % N. One or two recrystallizations will improve the quality of analytical grade reagents to the above level or better. Dissolve 16g of the persulphate in lOOmL of pure water at 70-80 °C. Cool the clear solution to almost 0 °C and filter. Dry the recrystallized salt in a desiccator over anhydrous CaCl2. The recovery is about 80 %. 

On electrolysing a cool solution of potassium hydrogen sulphate, the discharged anions combine to form peroxodisulphate (persulphate) ions. 

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