Aperoxy acid (often spelled as one word,peroxyacid, and sometimes calledperacid) is anacid which contains an acidic−OOH group. The two main classes are those derived from conventionalmineral acids, especiallysulfuric acid, and the peroxy derivatives of organiccarboxylic acids. They are generally strongoxidizers.
Peroxymonosulfuric acid (Caro's acid) is probably the most important inorganic peracid, at least in terms of its production scale.[1] It is used for the bleaching ofpulp and for the detoxification of cyanide in the mining industry. It is produced by treating sulfuric acid withhydrogen peroxide.Peroxymonophosphoric acid (H3PO5) is prepared similarly.[2]
Some peroxy acids are only hypothetical, but their anions are known. This is the case forperoxycarbonate[3] andperborate (seesodium perborate).[4]
Several organic peroxyacids are commercially useful.[5] They can be prepared in several ways. Most commonly, peracids are generated by treating the correspondingcarboxylic acid with hydrogen peroxide:[6]
A related reaction involves treatment of the carboxylic anhydride:
This method is popular for converting cyclic anhydrides to the corresponding monoperoxyacids, for example monoperoxyphthalic acid.
The third method involves treatment ofacid chlorides:
meta-Chloroperoxybenzoic acid (mCPBA) is prepared in this way:[7]
A related method starts with the peroxyanhydride.[8]
Aromaticaldehydes can beautoxidized to give peroxycarboxylic acids:
The products, however, react with the initial aldehyde forming the carboxylic acid:
In terms of acidity, peroxycarboxylic acids are about 1000 times weaker than the parent carboxylic acid, due to the absence ofresonance stabilization of the anion. For similar reasons, their pKa 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, thePrilezhaev reaction.
Another common reaction is conversion of cyclic ketones to the ring-expanded esters using peracids in aBaeyer-Villiger oxidation. They are also used for the oxidation ofamines andthioethers toamine oxides andsulfoxides. The laboratory applications of the valued reagentmCPBA illustrate these reactions.
Reaction of peroxycarboxylic acids with acid chlorides affords diacyl peroxides:
The oxidizing tendency of peroxides is related to theelectronegativity of the substituents.Electrophilic peroxides are stronger oxygen-atom transfer agents. The oxygen-atom donor tendency correlates with theacidity of theO−H bond. Thus, the order of oxidizing power isCF3CO3H > CH3CO3H > H2O2.
Peroxycarboxylic acids are available in both solid and liquid forms. Due to their oxidizing and disinfecting properties, they can be used in both professional and domestic settings.[9]
Peroxycarboxylic acids are bleaching agents and are used globally, particularly for tooth whitening. They are employed in various concentrations in dentistry to effectively bleach teeth. Lower concentrations are common for home use. Compared to hydrogen peroxide, peroxycarboxylic acids are approved as cosmetics in Europe under Regulation (EC) No. 1223/2009 of the European Parliament.[10]
In healthcare, peroxycarboxylic acids are primarily used for wound disinfection and cleaning contact lenses.
Peroxycarboxylic acids are also found in cleaning agents, disinfectants, and detergents, as they reliably kill germs and bacteria.
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