Peroxymonosulfuric acid

Peroxymonosulfuric acid, also known as persulfuric acid, peroxysulfuric acid is the inorganic compound with the formula H₂SO₅. It is a white solid. It is a component of Caro's acid, which is a solution of peroxymonosulfuric acid in sulfuric acid containing small amounts of water. Peroxymonosulfuric acid is a very strong oxidant (E⁰ = 2.51 V).

Structure

In peroxymonosulfuric acid, the S(VI) center adopts its characteristic tetrahedral geometry; the connectivity is indicated by the formula HO–O–S(O)₂–OH. The S-O-H proton is more acidic.

History

The German chemist Heinrich Caro first reported investigations of mixtures of hydrogen peroxide and sulfuric acid.

Synthesis and production

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

H₂O₂ ClSO₂OH ⇌ H₂SO₅ HCl

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 route employs the following reaction:

H₂O₂ H₂SO₄ ⇌ H₂SO₅ H₂O

This reaction is related to "piranha solution".

Uses in industry

H
₂SO
₅ and Caro's acid have been used for a variety of disinfectant and cleaning applications, e.g., swimming pool treatment and denture cleaning. It is used in gold mining to destroy the cyanide in the waste stream ("Tailings").

Alkali metal salts of H
₂SO
₅, especially oxone, are widely investigated.

Hazards

These peroxy acids can be explosive. Explosions have been reported at Brown University and Sun Oil. As with all strong oxidizing agents, peroxysulfuric acid is incompatible with organic compounds.