Thioglycolic acid

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Thioglycolic acid
IUPAC name
Sulfanylacetic acid
Other names
2-Mercaptoacetic acid
2-Sulfanylacetic acid
Acetyl mercaptan
Mercaptoacetic acid
Thioglycolic acid
Thiovanic acid
Molar mass 92.11 g/mol
Appearance Colorless liquid
Odor Unpleasant, sulfurous
Density 1.3253 g/cm3 (20 °C)[1]
Melting point −16 °C (3 °F; 257 K)
Boiling point 96 °C (205 °F; 369 K) (at 5 mmHg)
Solubility Reacts with amines
Miscible with acetone, benzene, chloroform, diethyl ether, ethanol, formic acid, isopropanol, toluene
Immiscible with aliphatic hydrocarbons
Vapor pressure 10 mmHg (17.8 °C)
Acidity (pKa) 3.83
Safety data sheet Sigma-Aldrich
Lethal dose or concentration (LD, LC):
261 mg/kg (rat, oral)
Related compounds
Related compounds
Glycolic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Thioglycolic acid (TGA) or mercaptoacetic acid (MAA) is an organic compound, carboxylic acid with a thiol group. It has the chemical formula C2H4O2S or HSCH2COOH.



Thioglycolic acid is about 100 times stronger acid than acetic acid, with a pKa of 3.83.

Thioglycolic acid is a reducing agent, especially at higher pH.

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 is a colorless liquid, with an unpleasant odor.


Thioglycolic acid and its esters are commonly used in hair removing products.

Some rust removers or car tar removers contain 5-10% sodium thioglycolate. To obtain the free acid, simply add a weak acid to the salt and purify the reaction product.

Thioglycolic acid is sold by chemical suppliers.


Thioglycolic acid is prepared by reaction of sodium or potassium chloracetate 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.


  • Chemical depilation
  • Hair permanent
  • Make ammonium thioglycolate
  • PVC stabilizer
  • Make thioglycolate broth



Thioglycolic acid is harmful and its strong unpleasant odor may cause health problems.


Thioglycolic acid should be kept in dark amber bottles, which must be airtight, as the compounds oxidizes in air over time. It is known to oxidize faster in the presence of water.


Should be neutralized with hydrogen peroxide or bleach to a less smelly form, then poured down the drain.


  1. Klason; Carlson; Chemische Berichte; vol. 39; (1906); p. 739

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