chemistry

Thioglycolic acid

Thioglycolic 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 Thioglycolic acid rather than just read about it. In short: Thioglycolic acid (TGA) is the organic compound HSCH2CO2H. TGA is often called mercaptoacetic acid (MAA).

Key takeaways

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

Reference excerpt

Thioglycolic acid (TGA) is the organic compound HSCH2CO2H. TGA is often called mercaptoacetic acid (MAA). It contains both a thiol (mercaptan) and carboxylic acid functional groups. It is a colorless liquid with a strongly unpleasant odor. TGA is miscible with polar organic solvents.

Uses TGA is used as a chemical depilatory and is still used as such, especially in salt forms, including calcium thioglycolate and sodium thioglycolate. TGA is the precursor to ammonium thioglycolate, which is used for permanents. TGA and its derivatives break the disulfide bonds in the cortex of hair. One reforms these broken bonds in giving hair a "perm". Alternatively and more commonly, the process leads to depilation, as is done commonly in leather processing. It is also used as an acidity indicator, manufacturing of thioglycolates, and in bacteriology for preparation of thioglycolate media. Thioglycolysis reactions are used on condensed tannins to study their structure. TGA has also been used to soften nails, either to reshape pincer nails into the correct position or to help the topical antifungal agent terbinafine penetrate the nail. Organotin derivatives of thioglycolic acid isooctyl esters are widely used as stabilizers for PVC. These species have the formula R2Sn(SCH2CO2C8H17)2. Sodium thioglycolate is a component of thioglycolate broth, a special bacterial growth media. It is also used in so-called "fallout remover" or "wheel cleaner" to remove iron oxide residue from wheels. Ferrous iron combines with thioglycolate to form red-violet ferric thioglycolate.

Production Thioglycolic acid is prepared by reaction of sodium or potassium chloroacetate with alkali metal hydrosulfide in aqueous medium. It can be also prepared via the Bunte salt obtained by reaction of sodium thiosulfate with chloroacetic acid:

ClCH2CO2H + Na2S2O3 → Na[O3S2CH2CO2H] + NaCl Na[O3S2CH2CO2H] + H2O → HSCH2CO2H + NaHSO4

Reactions Thioglycolic acid with a pKa of 3.83 is an acid about 8.5 times stronger than acetic acid (pKa 4.76):

HSCH2CO2H → HSCH2CO2− + H+ The second ionization has a pKa of 9.3:

HSCH2CO2− → −SCH2CO2− + H+ Thioglycolic acid is a reducing agent, especially at higher pH. It oxidizes to the corresponding disulfide (2-[(carboxymethyl)disulfanyl]acetic acid or dithiodiglycolic acid):

2 HSCH2CO2H + "O" → [SCH2CO2H]2 + H2O

With metal ions Thioglycolic acid, usually as its dianion, forms complexes with metal ions. Such complexes have been used for the detection of iron, molybdenum, silver, and tin. Thioglycolic acid reacts with diethyl acetylmalonate to form acetylmercaptoacetic acid and diethyl malonate, the reducing agent in the conversion of Fe(III) to Fe(II).

History Scientist David R. Goddard, in the early 1930s, identified TGA as a useful reagent for reducing the disulfide bonds in proteins, including keratin (hair protein), while studying why protease enzymes could not easily digest hair, nails, feathers, and such. He realized that while the disulfide bonds, which stabilize proteins by cross-linking, were broken, the structures containing these proteins could be reshaped easily, and that they would retain this shape after the disulfide bonds were allowed to re-form. TGA was developed in the 1940s for use as a chemical depilatory.

Safety and detection The LD50 (oral, rat) is 261 mg/kg, LC50 inhalation for rat is 21 mg/m3 for 4 h, and LD50 dermal for rabbit is 848 mg/kg. Mercaptoacetic acid in hair waving and depilatory products containing other mercapto acids can be identified by using thin-layer chromatography and gas chromatography. MAA also has been identified by using potentiometric titration with silver nitrate solution.

See also Ammonium thioglycolate Glycolic acid Thiolactic acid Dithiothreitol

References

Further reading Okada K, Okada E. Novel treatment using thioglycolic acid for pincer nails. J. Dermatol. 2012, volume 39, pp. 996-999.

Illustrations

Worked examples

Example 1 — a first encounter with Thioglycolic acid

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

In research: Thioglycolic 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 Thioglycolic 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: Thioglycolic acid is common in secondary-school and first-year university syllabi. It links to neighbouring topics Acetic acids, Chelating agents, Foul-smelling chemicals, so understanding it makes those chapters shorter.
In everyday life: Look for Thioglycolic 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.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Thioglycolic acid” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Thioglycolic acid in 20 minutes

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

Frequently asked questions

What is Thioglycolic acid in simple terms?

Thioglycolic acid (TGA) is the organic compound HSCH2CO2H. TGA is often called mercaptoacetic acid (MAA).

Why does Thioglycolic 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 Thioglycolic 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 Thioglycolic acid.