chemistry

Glycolic acid

Glycolic 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 Glycolic acid rather than just read about it. In short: Glycolic acid (or hydroxyacetic acid; chemical formula HOCH2CO2H) is a colorless, odorless and hygroscopic crystalline solid that is highly soluble in water. It is used in various skin-care products.

Key takeaways

Glycolic 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 Glycolic acid to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Glycolic acid from memory before moving on to harder problems.

Reference excerpt

Glycolic acid (or hydroxyacetic acid; chemical formula HOCH2CO2H) is a colorless, odorless and hygroscopic crystalline solid that is highly soluble in water. It is used in various skin-care products. Glycolic acid is widespread in nature. A glycolate (sometimes spelled "glycollate") is a salt or ester of glycolic acid.

History The name "glycolic acid" was coined in 1848 by French chemist Auguste Laurent (1807–1853). He proposed that the amino acid glycine—which was then called glycocolle—might be the amine of a hypothetical acid, which he called "glycolic acid" (acide glycolique). Glycolic acid was first prepared in 1851 by German chemist Adolph Strecker (1822–1871) and Russian chemist Nikolai Nikolaevich Sokolov (1826–1877). They produced it by treating hippuric acid with nitric acid and nitrogen dioxide to form an ester of benzoic acid and glycolic acid (C6H5C(=O)OCH2COOH), which they called "benzoglycolic acid" (Benzoglykolsäure; also benzoyl glycolic acid). They boiled the ester for days with dilute sulfuric acid, thereby obtaining benzoic acid and glycolic acid (Glykolsäure).

Preparation Glycolic acid can be synthesized in various ways. The predominant approaches use a catalyzed reaction of formaldehyde with synthesis gas (carbonylation of formaldehyde), for its low cost. It is also prepared by the reaction of chloroacetic acid with sodium hydroxide, followed by re-acidification. Other methods, not noticeably in use, include hydrogenation of oxalic acid, and hydrolysis of the cyanohydrin derived from formaldehyde. Some of today's glycolic acids are formic acid-free. Glycolic acid can be isolated from natural sources, such as sugarcane, sugar beets, pineapple, cantaloupe, and unripe grapes. Glycolic acid can also be prepared using an enzymatic biochemical process that may require less energy.

Properties Glycolic acid is slightly stronger than acetic acid due to the electron-withdrawing power of the terminal hydroxyl group. The carboxylate group can coordinate to metal ions, forming coordination complexes. Of particular note are the complexes with Pb2+ and Cu2+, which are significantly stronger than complexes with other carboxylic acids. This indicates that the hydroxyl group is involved in complex formation, possibly with the loss of its proton.

Applications Glycolic acid is used in the textile industry as a dyeing and tanning agent.

Organic synthesis Glycolic acid is a useful intermediate for organic synthesis, in a range of reactions including: oxidation-reduction, esterification, and long chain polymerization. It is used as a monomer in the preparation of polyglycolic acid and other biocompatible copolymers (e.g. PLGA). Commercially, important derivatives include the methyl (CAS# 96-35-5) and ethyl (CAS# 623-50-7) esters which are readily distillable (boiling points 147–149 °C and 158–159 °C, respectively), unlike the parent acid. The butyl ester (b.p. 178–186 °C) is a component of some varnishes, being desirable because it is nonvolatile and has good dissolving properties. Glycolide is the cyclic dimer, a bislactone, which is used in some of the polymerization processes.

Occurrence Plants produce glycolic acid during photorespiration. It is recycled by conversion to glycine within the peroxisomes and to tartronic acid semialdehyde within the chloroplasts. Because photorespiration is a wasteful side reaction in regard to photosynthesis, much effort has been devoted to suppressing its formation. One process converts glycolate into glycerate without using the conventional BASS6 and PLGG1 route; see glycerate pathway.

Safety Glycolic acid is an irritant to the skin. It occurs in all green plants.

References

External links Glycolic acid MS Spectrum Hazardous Substances Data Bank

Illustrations

Worked examples

Example 1 — a first encounter with Glycolic acid

Start with the simplest possible case. Write down what Glycolic 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 Glycolic 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 Glycolic 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 Glycolic acid

In research: Glycolic 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 Glycolic 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: Glycolic acid is common in secondary-school and first-year university syllabi. It links to neighbouring topics Alpha hydroxycarboxylic acids, Anti-acne preparations, Organic compounds with 2 carbon atoms, so understanding it makes those chapters shorter.
In everyday life: Look for Glycolic 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 Glycolic acid in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Glycolic 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 Glycolic acid out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Glycolic acid in simple terms?

Glycolic acid (or hydroxyacetic acid; chemical formula HOCH2CO2H) is a colorless, odorless and hygroscopic crystalline solid that is highly soluble in water. It is used in various skin-care products.

Why does Glycolic 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 Glycolic 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 Glycolic acid.