Peroxymonosulfuric acid
Encyclopedia
Peroxymonosulfuric acid, also known as persulfuric acid, peroxysulfuric acid, or as Caro's acid, is H2SO5, a liquid at room temperature. In this acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...

, 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 (Eº + 1.81 V) and highly explosive.

H2SO5 is sometimes confused with H2S2O8, known as peroxydisulfuric acid
Peroxydisulfuric acid
Peroxydisulfuric acid is a sulfur oxoacid with the chemical formula H2S2O8. It is also called Marshall's acid. In structural terms it can be written HO3SOOSO3H. It contains sulfur in its +6 oxidation state, but it also contains peroxide ions, which is why it appears to be in a higher oxidation...

. 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 by Heinrich Caro
Heinrich Caro
Heinrich Caro , was a German chemist.He started his study of chemistry at the Friedrich Wilhelms University and later chemistry and dyeing in Berlin at the Royal Trades Institute...

, after whom it is named.

Synthesis and production

The laboratory scale preparation of Caro's acid involve the combination of chlorosulfuric acid
Chlorosulfuric acid
Chlorosulfuric acid is the inorganic compound with the formula HSO3Cl. It is also known as chlorosulfonic acid. It is a distillable, colorless liquid that should be handled with care. It is a hygroscopic and a powerful lachrymator.-Structure and properties:Chlorosulfuric acid is a tetrahedral...

 and hydrogen peroxide
Hydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...

.
H2O2 + ClSO2OH H2SO5 + HCl


Large scale production of Caro's acid is usually done on site, due to its instability. According to the patent by Martin, Caro's acid is produced by reacting >85% sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...

 and >50% hydrogen peroxide ("Piranha solution
Piranha solution
Piranha solution, also known as piranha etch, is a mixture of sulfuric acid and hydrogen peroxide , used to clean organic residues off substrates...

").
H2O2 + H2SO4 H2SO5 + H2O

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
Lignin
Lignin or lignen is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants and some algae. The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum, meaning wood...

 of wood.

Ammonium
Ammonium
The ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...

, sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

, and potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...

 salts of H2SO5 are used in the plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

s industry as polymerization
Polymerization
In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains...

 initiators, etchants, desizing agents, soil conditioner
Soil conditioner
A soil conditioner, also called a soil amendment, is a material added to soil to improve plant growth and health. A conditioner or a combination of conditioners corrects the soil's deficiencies in structure and-or nutrients.-Purpose:...

, and for decolorizing and deodorizing oils.

Potassium peroxymonosulfate
Potassium peroxymonosulfate
Potassium peroxymonosulfate is widely used as an oxidizing agent...

, KHSO5, is the potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...

 acid salt
Acid salt
Acid salt is a somewhat obscure term for a class of salts formed by the partial neutralization of diprotic or polyprotic acids. Because the parent acid is only partially neutralized, one or more replaceable hydrogen atoms remain. Typical acid salts have one or more alkali metal ions as well as one...

 of peroxymonosulfuric acid. It is widely used as an oxidizing agent
Oxidizing agent
An oxidizing agent can be defined as a substance that removes electrons from another reactant in a redox chemical reaction...

.

Dangers

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 the compound, creating a highly unstable molecule such as acetone peroxide
Acetone peroxide
Acetone peroxide is an organic peroxide and a primary high explosive. It takes the form of a white crystalline powder with a distinctive bleach-like odor....

.
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