chemistry

Peroxy acid

Peroxy acid is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Peroxy acid rather than just read about it. In short: 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, and the peroxy derivatives of organic carboxylic acids.

Key takeaways

Peroxy acid belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Peroxy acid to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Peroxy acid from memory before moving on to harder problems.

Reference excerpt

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, and the peroxy derivatives of organic carboxylic acids. They are generally strong oxidizers.

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 with hydrogen peroxide. Peroxymonophosphoric acid (H3PO5) is prepared similarly. Some peroxy acids are only hypothetical, but their anions are known. This is the case for peroxycarbonate and perborate (see sodium perborate).

Organic peracids

Production 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 acyl chlorides:

RC(O)Cl + H2O2 → RCO3H + HCl meta-Chloroperoxybenzoic acid (mCPBA) 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 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 stabilization of the anion. For similar reasons, their pKa values tend also to be relatively insensitive to substituents; all are between 7.2 and 8.2. 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 amines and thioethers to amine oxides and sulfoxides. The laboratory applications of the valued reagent mCPBA 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.

Usage 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.

Bleaching agents 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.

Disinfectants 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.

See also Organic peroxide Peracetic acid Peroxyacyl nitrates

References

Illustrations

Worked examples

Example 1 — a first encounter with Peroxy acid

Start with the simplest possible case. Write down what Peroxy acid claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Peroxy acid before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Peroxy acid ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Peroxy acid

In research: Peroxy acid appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Peroxy acid in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Peroxy acid is common in secondary-school and first-year university syllabi. It links to neighbouring topics Organic peroxy acids, Peroxy acids, so understanding it makes those chapters shorter.
In everyday life: Look for Peroxy acid outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Peroxy acid in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Peroxy acid means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Peroxy acid out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Peroxy acid in simple terms?

Why does Peroxy acid matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Peroxy acid?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Peroxy acid.