Thioglycolic acid:Functions,Preparation and Side effects

Thioglycolic acid is a colorless liquid with an unpleasantodor (like rotten eggs). It is used in making hair dressingsolutions, pharmaceuticals and chemicals.

Functions

Thioglycolic acid is a chemical compound commonly used in cosmetics, particularly in hair removal products. Its primary function is to break down the protein structure of hair, making it more pliable and easier to remove. Thioglycolic acid is a key component in depilatory creams and lotions, where it works by disrupting the disulfide bonds in the keratin protein of hair. This chemical reaction weakens the hair shaft, allowing for mechanical removal or its dissolution. While effective in hair removal, products containing thioglycolic acid should be used with caution, as they may cause skin irritation.

Preparation

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

Side effects

Thioglycolic acid is toxic corrosives. Ingestions can cause irritation of the mouth and throat accompanied by nausea, vomiting, and possibly diarrhea. Thioglycolate can cause immediate-type hypersensitivity reaction. In large amounts, it can cause hypoglycemia and cyanosis.[1]

Reference

[1] Caraccio, T. and R. Mcfee.“Cosmetics and Toilet Articles.”1900. 0.

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