Chemical Concepts Related To Perms
When discussing the chemistry of perms, one should consider two chemical facts. First is the thiol-disulfide equilibrium:
- RSH + R'SSR' ⇌ R'SH + RSSR'
where R and R' are organic substituents such as methyl (-CH3), ethyl (-C2H5), or -CH2COO−.
The thiol-disulfide exchange reaction is accelerated by bases such as ammonia, because the base generates some thiolate anion (RS-), which attacks the disulfide. Thus the ammonia plays multiple roles (and more, see below) in this application.
The second chemical fact is that polar molecules are less volatile than nonpolar ones. So the glycolate substituent makes the thiol non-volatile and hence non-odorous. An added advantage is that the glycolate confers some solubility in water. One could almost certainly use HSCH3 and ammonia to give a perm, but there would be serious olfactory consequences.
Read more about this topic: Ammonium Thioglycolate
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