Wikipedia
Peroxydisulfuric acid
Peroxydisulfuric acid is the inorganic compound with the chemical formula HSO. Also called Marshall's acid, it is sulfur oxoacid. In structural terms it can be written HOSOOSOH. It contains sulfur in its +6 oxidation state and a peroxide group. Its salts, commonly known as persulfates, are industrially important as powerful oxidizing agents.
The acid is prepared by the reaction of chlorosulfuric acid with hydrogen peroxide:
2ClSOH + HO → HSO + 2 HCl