A peroxy acid (often spelled as one word, peroxyacid, and sometimes called peracid) is an acid which contains an acidic –OOH group. The two main classes are those derived from conventional

mineral acid A mineral acid (or inorganic acid) is an acid derived from one or more inorganic compounds, as opposed to organic acids which are acidic, organic compounds. All mineral acids form hydrogen ions and the conjugate base when dissolved in water. Cha ...

s, especially sulfuric acid, and the peroxy derivatives of organic carboxylic acids. They are generally strong

oxidizer An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ). In other words, an oxid ...

Inorganic peroxy acids

Peroxymonosulfuric acid (Caro's acid) is probably the most important inorganic peracid, at least in terms of its production scale. It is used for the bleaching of

pulp Pulp may refer to: * Pulp (fruit), the inner flesh of fruit Engineering * Dissolving pulp, highly purified cellulose used in fibre and film manufacture * Pulp (paper), the fibrous material used to make paper * Molded pulp, a packaging material ...

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

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%� ...

. Peroxymonophosphoric 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 with hydrogen peroxide: :RCO₂H + H₂O₂ RCO₃H + H₂O A related reaction involves treatment of the carboxylic anhydride: :(RCO)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 chloride In organic chemistry, an acyl chloride (or acid chloride) is an organic compound with the functional group . Their formula is usually written , where R is a side chain. They are reactive derivatives of carboxylic acids (). A specific example o ...

s: :RC(O)Cl + H₂O₂ → RCO₃H + HCl ''meta''-Chloroperoxybenzoic acid (''m''CPBA) is prepared in this way. A related method starts with the peroxyanhydride. Aromatic

aldehydes In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl grou ...

can be autoxidized to give peroxycarboxylic acids: :Ar-CHO + O₂ → Ar-COOOH (Ar =

aryl In organic chemistry, an aryl is any functional group or substituent derived from an aromaticity, aromatic ring, usually an aromatic hydrocarbon, such as phenyl and naphthyl. "Aryl" is used for the sake of abbreviation or generalization, and "Ar ...

group) The products, however, react with the initial aldehyde forming the carboxylic acid: :Ar-COOOH + Ar-CHO → 2 Ar-COOH

Properties and uses

In terms of acidity, peroxycarboxylic acids are about 1000 times weaker than the parent carboxylic acid, due to the absence of

resonance Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied Periodic function, periodic force (or a Fourier analysis, Fourier component of it) is equal or close to a natural frequency of the system ...

stabilization of the anion. For similar reasons, their p''K''_a values tend also to be relatively insensitive to substituents. The most common use of organic peroxy acids is for the conversion of alkenes to epoxides, the

Prilezhaev reaction The Prilezhaev reaction, also known as the Prileschajew reaction or Prilezhaev epoxidation, is the chemical reaction of an alkene with a peroxy acid to form epoxides. It is named after Nikolai Prilezhaev, who first reported this reaction in 1909 ...

. Another common reaction is conversion of cyclic ketones to the ring-expanded esters using peracids in a Baeyer-Villiger oxidation. They are also used for the oxidation of

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen Hydrogen is the chemical element wi ...

s and

thioether In organic chemistry, an organic sulfide (British English sulphide) or thioether is an organosulfur functional group with the connectivity as shown on right. Like many other sulfur-containing compounds, volatile sulfides have foul odors. A su ...

s to

amine oxide In chemistry, an amine oxide, also known as an amine ''N''-oxide or simply ''N''-oxide, is a chemical compound that contains the functional group , a nitrogen-oxygen coordinate covalent bond with three additional hydrogen and/or substituent-grou ...

s and sulfoxides. The laboratory applications of the valued reagent ''m''CPBA illustrate these reactions. Reaction of peroxycarboxylic acids with acid chlorides affords diacyl peroxides: :RC(O)Cl + RC(O)O₂H → (RC(O))₂O₂ + HCl The oxidizing tendency of peroxides is related to the

electronegativity Electronegativity, symbolized as , is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the ...

of the substituents. Electrophilic peroxides are stronger oxygen-atom transfer agents. The oxygen-atom donor tendency correlates with the

acidity In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a ...

of the O−H bond. Thus, the order of oxidizing power is CF₃CO₃H > CH₃CO₃H > H₂O₂.

References

{{DEFAULTSORT:Peroxy Acid Organic peroxy acids Oxidizing agents

Inorganic peroxy acids

Organic peracids

Properties and uses

See also

References