Potassium Thioglycolate, Potassium Mercaptoacetate, Potassium Sulfanylacetate, 34452-51-2

Potassium Thioglycolate, Potassium Mercaptoacetate, Potassium Sulfanylacetate, 34452-51-2

Potassium Thioglycolate Monograph

1. General Information and Identification

Potassium Thioglycolate is the potassium salt of thioglycolic acid (mercaptoacetic acid). It is an organic compound widely recognized for its ability to break down disulfide bonds in keratin, making it a key active ingredient in the cosmetic industry, particularly for depilatory and hair straightening products.

• IUPAC Name: Potassium 2-sulfanylacetate (or Potassium 2-mercaptoacetate)

• Common Names:

  • Potassium Mercaptoacetate

  • Thioglycolic Acid, Potassium Salt

  • Acetic Acid, Mercapto-, Monopotassium Salt

  • Potassium 2-sulfanylacetate

• CAS Number: 34452-51-2

• Molecular Formula: C₂H₃KO₂S

• Molecular Weight: 130.21 g/mol

2. Chemical Classification and Structure

• Chemical Class: Organopotassium compound; Thiol (Mercaptan) derivative

• Related Compound: Thioglycolic Acid (HS-CH₂-COOH)

As a salt, it exists in an ionic form: K⁺ [⁻S-CH₂-COO⁻]. The key functional group is the thiol group (-SH) (or its ionized form, thiolate -S⁻), which is responsible for its reducing activity. This allows it to cleave the disulfide bonds (-S-S-) in the keratin protein structure.

3. Comparison with Calcium Thioglycolate

• Preference: Potassium Thioglycolate is generally less preferred compared to its "sister product," Calcium Thioglycolate, for some applications.

• Reason: Calcium Thioglycolate is often considered more effective or provides different formulation characteristics (such as cream consistency).

• Key Difference: The most significant distinction lies in the active ingredient concentration. Potassium Thioglycolate solutions typically have a lower concentration of the active thiol compound compared to equivalent calcium-based formulations.

  • Example: A standard 42% Potassium Thioglycolate solution contains approximately 30% Thioglycolic Acid equivalent.

4. Production Method

• Synthesis: Potassium Thioglycolate is produced by reacting Thioglycolic Acid (TGA) with a potassium-containing base (such as Potassium Hydroxide, KOH).

  • Reaction: HS-CH₂-COOH + KOH → HS-CH₂-COOK + H₂O

• Note: Specific industrial synthesis details (catalysts, purification steps) are often proprietary and not widely published.

5. Physical and Chemical Properties

• Appearance: Typically exists as a liquid with a color ranging from clear to light pink.

• Odor: Possesses a strong, characteristic, unpleasant odor often described as "sulfurous" or reminiscent of rotten eggs, which is typical for thiol-containing compounds.

• Melting Point: 226 °C to 229 °C (for the pure solid salt; however, it is commercially handled in solution).

• Solubility: Highly soluble in water.

• Density: Approximately 1.311 g/cm³ (for the concentrated solution).

• Concentration: Commercial grades are often supplied as an aqueous solution, with 42% being a common concentration standard. In this 42% solution, the active Thioglycolic Acid content is roughly 30%.

• pH: The solution is alkaline.

6. Mechanism of Action

Potassium Thioglycolate works by reducing (breaking) the disulfide bonds present in the keratin protein structure of hair.

1. Hair gets its strength and shape from these cross-linking disulfide bonds.

2. The thiol group (-SH) in Potassium Thioglycolate attacks these bonds, converting them into thiol groups (-SH).

3. This chemical reduction weakens the hair fiber, making it soft, brittle, and easily broken or mechanically manipulated.

7. Applications and Uses

Potassium Thioglycolate is used almost exclusively in cosmetic and personal care formulations.

• Depilatory Creams (Hair Removal): This is its primary use. It serves as the main active ingredient in creams, lotions, and aerosol foams designed to remove unwanted body hair. By breaking down the keratin, the hair turns into a gelatinous mass that can be easily wiped away.

• Hair Straightening/Relaxing Products: It is used to chemically straighten curly or wavy hair. The cream breaks the natural disulfide bonds; the hair is then mechanically straightened (e.g., with a comb), and a neutralizing (oxidizing) agent is applied to reform the bonds in the new, straight position.

• Formulation Variations: Depilatory products containing Potassium Thioglycolate can be found in several forms:

  • Standard cream format

  • Aerosol (foam)

  • Shower cream (wash-off depilatories)

• Combination with Other Agents: In some formulations, it is modified or combined with Calcium Thioglycolate to adjust efficacy and texture. Products may also include soothing agents like Lidocaine to reduce skin irritation during the hair removal process.

• Dermatological Preparations: It can be a component in medications or peels formulated for the treatment of comedones (clogged pores), acne lesions, and blemished skin. Its keratolytic property (ability to break down keratin) helps in exfoliating dead skin cells and unclogging pores. (Note: Calcium Thioglycolate is a common alternative in this specific category).

8. Safety and Handling

• Skin Irritant: Potassium Thioglycolate is a strong alkali and can cause significant skin irritation, burns, and allergic reactions if left on the skin for too long or used incorrectly.

• Corrosive: It is corrosive to eyes and mucous membranes.

• Usage Instructions: Depilatory products must be used strictly according to package directions (usually applied for a maximum of 5-10 minutes) and never used on broken, irritated, or sunburned skin. A patch test is highly recommended before first use.

• Odor Control: Due to its strong thiol odor, cosmetic formulations often contain significant amounts of fragrances to mask the smell.

• Storage: Should be stored in tightly sealed containers, away from air (oxidation) and light, in a cool place.