Thioglycolic acid

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"Thioglycolate" redirects here. For the microbiology broth, see thioglycollate broth.
Thioglycolic acid[1]
Thioglycolic acid.png
Space-filling model of thioglycolic acid
Identifiers
CAS number 68-11-1 YesY
PubChem 1133
ChemSpider 1101 YesY
UNII 7857H94KHM YesY
KEGG C02086 YesY
ChEBI CHEBI:30065 YesY
ChEMBL CHEMBL116455 YesY
Jmol-3D images Image 1
Properties
Molecular formula C2H4O2S
Molar mass 92.12 g mol−1
Density 1.32 g/cm3
Melting point −16 °C (3 °F; 257 K)
Boiling point 96 °C at 5 mmHg
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references

Thioglycolic acid (TGA) is the organic compound HSCH2CO2H. TGA is often called Mercaptoacetic acid (MAA). It contains both a thiol (mercaptan) and a carboxylic acid. It is a clear liquid with a strong unpleasant odor. It is also combustible. It is readily oxidized by air to the corresponding disulfide [SCH2CO2H]2.

The 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.[3]

TGA was developed in the 1940s for use 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 that 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.

TGA is also used in the making of tin stabilizers often used in certain polyvinyl chloride products (such as vinyl siding).

TGA, 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 used as nucleophile in thioglycolysis reactions used on condensed tannins to study their structure.

Uses[edit]

Applying TGA can soften nails and then fix pincer nails in the correct position.[4]

Synthesis[edit]

Thioglycolic acid could be prepared by reaction of sodium or potassium chloracetate with alkali metal hydrosulfide in aqueous medium.[5] It can be also prepared by interaction of sodium thiosulphate with chloroacetic acid.[6]

Reactions[edit]

TGA reacts with diethyl acetylmalonate to form acetylmercatoacetic acid and diethyl malonate, the reducing agent in conversion of Fe (III) to Fe (II).[7]

Solubility[edit]

TGA is miscible with acetone, ethanol, ethyl ether, other organic solvents and water. It is slightly soluble in chloroform.[8]

Identification[edit]

Mercaptoacetic acid in hair waving and depilatory products containing other mercapto acids can be identified by using thin-layer chromatography and gas chromatography.[9][10] MAA also has been identified by using potentiometric titration with silver nitrate solution.[11]

Safety[edit]

The LD50 Oral for rat is 114 mg/kg, LC50 inhalation for rat is 21 mg/m3 for 4 h, and LD50 dermal for rabbit is 848 mg/kg.[12]


See also[edit]

References[edit]

  1. ^ Merck Index, 11th Edition, 9265
  2. ^ CDC - NIOSH Pocket Guide to Chemical Hazards
  3. ^ National Academies Press:Biographical Memoirs:David Rockwell Goddard:by Ralph O. Erickson
  4. ^ Okada K, Okada E. Novel treatment using thioglycolic acid for pincer nails. J. Dermatol. 2012, 39, 996-999.
  5. ^ Cosmetic, Toiletry, and Fragrance Association (CTFA). Thioglycolic Acid. 1987;(1987a). Submission of unpublished data by CTFA Code No. 3-25-2
  6. ^ Saeed M. Hameed N. Madan V. Mansoor S. Preparation and Mechanisms studies of Thioglycolic Acid. Pak. J. Sci. Ind. Res. 1992, 35: 131-132
  7. ^ Lee CW, Phil M. The detection of iron traces on hands by ferrozine sparys: a report on the sensitivity and interference of the method and recommended procedure in forensic science investigation. J Forensic Sci. 1986, 31:920-930.
  8. ^ The Merck index, 14th ed.; O’Neil, Maryadele J., Ed.; Merck & Co., Inc.: Whitehouse Station, NJ, 2006; p 9342.
  9. ^ Goetz N, Gataud P, Bore P. Determination of mercaptoacetic acid in hair waving and depilatory products. Analyst. 1979,104:1062-1069
  10. ^ Goetz N, Gataud P, Bore P. Gas-chromatographic determination of mercaptoacetic acid in hair-waving and diplatory products. Cosmet Sci Technol Ser. 1985, 4:65-79.
  11. ^ Vandeputte M, Dryon L, Van Den Winkel P, Mertens J, Massart DL. Determination of thioglycolic acid using a silver sulfide single crystal electrode. Analysis. 1975,3:500-504.
  12. ^ Sigma-Aldrich MSDS. http://www.sigmaaldrich.com/safety-center.html?cm_sp=Search-_-MSDS-_-MSDS1 (accessed Nov 10, 2013). Product Number – T3758