Ammonium persufate

Ammonium persulfate (APS) is the inorganic compound with the formula (NH₄)₂S₂O₈. It is a colourless (white) salt that is highly soluble in water, much more so than the related potassium salt. It is a strong oxidizing agent that is used in polymer chemistry, as an etchant, and as a cleaning and bleaching agent.

The dissolution of the salt in water is an endothermic process.

As an oxidizing agent and a source of radicals, APS finds many commercial applications.

Salts of sulfate are mainly used as radical initiators in the polymerization of certain alkenes. Commercially important polymers prepared using persulfates include styrene-butadiene rubber and polytetrafluoroethylene. In solution, the dianion dissociates to give radicals:

[O₃SO–OSO₃]²⁻ ⇌ 2 [SO₄]^•−

The sulfate radical adds to the alkene to give a sulfate ester radical. It is also used along with tetramethylethylenediamine to catalyze the polymerization of acrylamide in making a polyacrylamide gel, hence being important for SDS-PAGE and western blot.

Illustrative of its powerful oxidizing properties, it is used to etch copper on printed circuit boards as an alternative to ferric chloride solution. This property was discovered many years ago. In 1908, John William Turrentine used a dilute ammonium persulfate solution to etch copper. Turrentine weighed copper spirals before placing the copper spirals into the ammonium persulfate solution for an hour. After an hour, the spirals were weighed again and the amount of copper dissolved by ammonium persulfate was recorded. This experiment was extended to other metals such as nickel, cadmium, and iron, all of which yielded similar results. The oxidation equation is thus: S₂O²⁻₈ (aq) +  e⁻ → 2 SO²⁻₄ (aq).

Ammonium persulfate is a standard ingredient in hair bleach.

Persulfates are used as oxidants in organic chemistry. For example, in the Minisci reaction.