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| Names | |
|---|---|
| Other names Perm salt | |
| Identifiers | |
3D model (JSmol) | |
| ChemSpider |
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| ECHA InfoCard | 100.024.128 |
| UNII | |
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| Properties | |
| C2H7NO2S | |
| Molar mass | 109.15 g/mol |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Ammonium thioglycolate, also known asperm salt, is thesalt ofthioglycolic acid andammonia. It has the formula HSCH2CO2NH4 and has use inperming hair.[1]
Being the salt of aweak acid andweak base, ammonium thioglycolate exists in solution as anequilibrium mixture of the salt itself as well as thioglycolic acid and ammonia:
Thioglycolate, in turn, is able to cleavedisulfide bonds, capping one side with a hydrogen and forming a new disulfide with the other side:
A solution containing ammonium thioglycolate contains a lot of free ammonia, which swellshair, rendering it permeable. Thethioglycolic acid in the perm solutionreduces the disulfidecystine bonds in thecortex of the hair.[2] In a sense, the thioglycolate removes crosslinks. After washing, the hair is treated with a mild solution ofhydrogen peroxide, which oxidizes thecysteines back tocystine. These new chemical bonds impart the structural rigidity necessary for a successful perm. The rigidification process is akin to thevulcanization of rubber, where commonly polysulfide linkages are used to crosslink the polymer chains. However, not as many disulfide bonds are reformed as there were before the permanent. As a result, the hair is weaker than before the permanent was applied and repeated applications over the same spot may eventually cause strand breakage.
Since polar molecules are less volatile than nonpolar ones, the glycolate substituent makes the thiol non-volatile and hence less odorous. An added advantage is that the glycolate confers some solubility in water. One could almost certainly useHSCH3 and ammonia to give a perm, but there would be serious olfactory consequences.
In the 2001 filmLegally Blonde, the protagonist, law student Elle Woods, wins her first case by proving that a witness who had gotten a perm the day of a murder could not have been in the shower at the time of the murder because "isn't the first cardinal rule of perm maintenance that you're forbidden to wet your hair for at least 24 hours after getting a perm at the risk of deactivating the ammonium thioglycolate?" (but mispronouncing it as "ammonium thyglockalate").
