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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 acids, especially
The third method involves treatment of acid chlorides: :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 can be autoxidized to give peroxycarboxylic acids: :Ar-CHO + O2 → Ar-COOOH (Ar =
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 acids, especially sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...
, 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 oxi ...
s.
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 and for the detoxification of cyanide in the mining industry. It is produced by treating sulfuric acid withhydrogen 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
Peroxymonophosphoric acid () is an oxyacid of phosphorus. It is a colorless viscous oil. Its salts are called peroxymonophosphates. Another peroxyphosphoric acid is peroxydiphosphoric acid, .
Preparation
Peroxyphosphoric acids were first syn ...
(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 chlorides: :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 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 aromatic ring, usually an aromatic hydrocarbon, such as phenyl and naphthyl. "Aryl" is used for the sake of abbreviation or generalization, and "Ar" is used ...
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 ofresonance
Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscil ...
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. 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 atoms have been replaced by a substituent ...
s and thioethers to amine oxides 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 of the substituents. Electrophilic peroxides are stronger oxygen-atom transfer agents. The oxygen-atom donor tendency correlates with the acidity of the O−H bond. Thus, the order of oxidizing power is CF3CO3H > CH3CO3H > H2O2.
See also
*Organic peroxide
In organic chemistry, organic peroxides are organic compounds containing the peroxide functional group (). If the R′ is hydrogen, the compounds are called hydroperoxides, which are discussed in that article. The O−O bond of peroxides easily b ...
* Peracetic acid
Peracetic acid (also known as peroxyacetic acid, or PAA) is an organic compound with the formula CH3CO3H. This peroxy acid is a colorless liquid with a characteristic acrid odor reminiscent of acetic acid. It can be highly corrosive.
Peracetic ...
* Peroxyacyl nitrates
References