Peroxy acid
A peroxy acid is an 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...

 which contains an acidic -OOH group. The two main classes are those derived from conventional mineral acids, especially sulfuric acid, and the organic derivatives of carboxylic acids. They are generally strong oxidizers.

Inorganic peroxy acids

Peroxysulfuric acid
Peroxysulfuric acid
Peroxysulfuric acid can refer to either of these chemical compounds:*Peroxymonosulfuric acid, H2SO5*Peroxydisulfuric acid, H2S2O8...

 (Caro's acid) is probably the most important inorganic peracid, at least in terms of the scale. It is used for the bleaching of pulp
Pulp (paper)
Pulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibres from wood, fibre crops or waste paper. Wood pulp is the most common raw material in papermaking.-History:...

 and for the detoxification of cyanide in the mining industry. It is produced by treating sulfuric acid with 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...

. Peroxyphosphoric acid (H3PO5) is prepared similarly.

Organic peracids

Several organic peroxyacids are commercially useful. They can be prepared in several ways. Most commonly, peracids are generated by treating the corresponding carboxylic acid
Carboxylic acid
Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...

 with hydrogen peroxide:
RCO2H + H2O2 RCO3H + H2O

A related reaction involves treatment of the carboxylic anhydride:2O + H2O2 → RCO3H + RCO2H
This method is popular for converting cyclic anhydrides to the corresponding monoperoxyacids, for example monoperoxyphthalic acid.
The third method involves treatment of acid chlorides:
RC(O)Cl + H2O2 → RCO3H + HCl

meta-chloroperoxybenzoic acid
Meta-Chloroperoxybenzoic acid
meta-Chloroperoxybenzoic acid is a peroxycarboxylic acid used widely as an oxidant in organic synthesis. mCPBA is often preferred to other peroxy acids because of its relative ease of handling...

 (mCPBA) is prepared in this way.

Properties and uses

Peroxycarboxylic acids are about 1000x weaker than the parent carboxylic acid, owing the absence of resonance stabilization of the anion. For similar reasons, their pKa's tend also to be relatively insensitive to the substituent R.

The largest use of organic peroxy acids is for the conversion of alkenes to epoxides. Certain cyclic ketones are converted to the ring-expanded esters using peracids in a Baeyer-Villiger oxidation
Baeyer-Villiger oxidation
The Baeyer–Villiger oxidation is an organic reaction in which a ketone is oxidized to an ester by treatment with peroxy acids or hydrogen peroxide. Key features of the Baeyer–Villiger oxidation are its stereospecificity and predictable regiochemistry...

. They are also used for the oxidation of amine
Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...

s and thioether
A thioether is a functional group in organosulfur chemistry with the connectivity C-S-C as shown on right. Like many other sulfur-containing compounds, volatile thioethers have foul odors. A thioether is similar to an ether except that it contains a sulfur atom in place of the oxygen...

s to amine oxide
Amine oxide
An amine oxide, also known as amine-N-oxide and N-oxide, is a chemical compound that contains the functional group R3N+-O−, an N-O bond with three additional hydrogen and/or hydrocarbon side chains attached to N. Sometimes it is written as R3N→O or, wrongly, as R3N=O.In the strict sense the...

s and sulfoxide
A sulfoxide is a chemical compound containing a sulfinyl functional group attached to two carbon atoms. Sulfoxides can be considered as oxidized sulfides...

s. The laboratory applications of the valued reagent mCPBA illustrate these reactions. It is used as a reagent
A reagent is a "substance or compound that is added to a system in order to bring about a chemical reaction, or added to see if a reaction occurs." Although the terms reactant and reagent are often used interchangeably, a reactant is less specifically a "substance that is consumed in the course of...

 in the Baeyer-Villiger oxidation and in oxidation of carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

-carbon double bond
Double bond
A double bond in chemistry is a chemical bond between two chemical elements involving four bonding electrons instead of the usual two. The most common double bond, that between two carbon atoms, can be found in alkenes. Many types of double bonds between two different elements exist, for example in...

s in alkene
In organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond...

s to generate epoxide
An epoxide is a cyclic ether with three ring atoms. This ring approximately defines an equilateral triangle, which makes it highly strained. The strained ring makes epoxides more reactive than other ethers. Simple epoxides are named from the parent compound ethylene oxide or oxirane, such as in...

s (oxiranes). Reaction of peroxycarboxylic acids with acid chlorides affords diacyl peroxides:
RC(O)Cl + RC2O2H → (RCO)2O2 + HCl

See also

  • Organic peroxide
    Organic peroxide
    Organic peroxides are organic compounds containing the peroxide functional group . If the R' is hydrogen, the compound is called an organic hydroperoxide. Peresters have general structure RCOOR. The O-O bond easily breaks and forms free radicals of the form RO·...

  • Meta-Chloroperoxybenzoic acid
    Meta-Chloroperoxybenzoic acid
    meta-Chloroperoxybenzoic acid is a peroxycarboxylic acid used widely as an oxidant in organic synthesis. mCPBA is often preferred to other peroxy acids because of its relative ease of handling...

  • Peracetic acid
  • Peroxyacyl nitrates
    Peroxyacyl nitrates
    Acyl peroxy nitrates, or Peroxyacyl nitrates , are powerful respiratory and eye irritants present in photochemical smog. They are produced by the gas-phase oxidation of a variety of volatile organic compounds , or by aldehydes and other oxygenated VOCs oxidizing in the presence of NO2...

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