Chemistry:Peroxymonosulfuric acid

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Short description: Powerful oxidizing agent
Peroxymonosulfuric acid
Skeletal formula of peroxymonosulfuric acid
Ball and stick model of peroxymonosulfuric acid
IUPAC names
Peroxysulfuric acid
Sulfuroperoxoic acid[1]
Systematic IUPAC name
Other names
Peroxosulfuric acid[1]
Peroxomonosulfuric acid
Persulfuric acid
Caro's acid
3D model (JSmol)
EC Number
  • 231-766-6
UN number 1483
Molar mass 114.078 g mol−1
Appearance White crystals
Density 2.239 g cm−3
Melting point 45 °C
Conjugate base Peroxomonosulfate
Tetrahedral at S
Main hazards strong oxidizer
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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 (E0 = +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.


H2SO5 was first described in 1898 by the German chemist Heinrich Caro, after whom it is named.[3]

Synthesis and production

The laboratory scale preparation of Caro's acid involves the combination of chlorosulfuric acid and hydrogen peroxide:

H2O2 + ClSO2OHH2SO5 + HCl [4]

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:

H2O2 + H2SO4H2SO5 + H2O [5]

This is the reaction that produces the acid transiently in "piranha solution".

Uses in industry

Ammonium, sodium, and potassium salts of H2SO5 are used in the plastics industry as radical initiators for polymerization. They are also used as etchants, oxidative desizing agents for textile fabrics, 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.


Pure Caro's acid is highly explosive. Explosions have been reported at Brown University[6] 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.

See also