Peroxymonosulfuric acid

Peroxymonosulfuric acid, (H2SO5), also known as persulfuric acid, peroxysulfuric acid, or Caro's acid. In this acid, the S(VI) center adopts its characteristic tetrahedral geometry; the connectivity is indicated by the formula HO–O–S(O)2–OH. It is one of the strongest oxidants known ("E"0 = +2.51 V) and is highly explosive.
H2SO5 is sometimes confused with H2S2O8, known as peroxydisulfuric acid. The disulfuric acid, which appears to be more widely used as its alkali metal salts, has the structure HO–S(O)2–O–O–S(O)2–OH.
History.
H2SO5 was first described in 1898 by Heinrich Caro, after whom it is named.
Synthesis and production.
The laboratory scale preparation of Caro's acid involves the combination of chlorosulfuric acid and hydrogen peroxide.
Published patents include more than one reaction for preparation of Caro's acid, usually as an intermediate for the production of potassium monopersulfate (PMPS), a bleaching and oxidizing agent. One patent for production of Caro's acid for this purpose gives the following reaction:
This is the reaction that produces the acid transiently in "piranha solution".
Uses in industry.
H2SO5 has been used for a variety of disinfectant and cleaning applications, e.g., swimming pool treatment and denture cleaning. Alkali metal salts of H2SO5 show promise for the delignification of wood. It is also used in laboratories as a last resort in removing organic materials since H2SO5 can fully oxidize any organic materials.
Ammonium, sodium, and potassium salts of H2SO5 are used in the plastic industry as polymerization initiators, etchants, desizing agents, soil conditioner, and for decolorizing and deodorizing oils.
Potassium peroxymonosulfate, KHSO5, is the potassium acid salt of peroxymonosulfuric acid. It is widely used as an oxidizing agent.
Hazards.
Pure Caro's acid is highly explosive. Explosions have been reported at Brown University and Sun Oil. As with all strong oxidizing agents, peroxysulfuric acid should be kept away from organic compounds such as ethers and ketones because of its ability to peroxidize these compounds, creating highly unstable molecules such as acetone peroxide.