Thioglycolic Acid

Thioglycolic acid (mercaptoacetic acid, CAS 68-11-1) is the free-acid form of the thioglycolate family. Its salts, ammonium thioglycolate and sodium thioglycolate, are the chemistry behind the classic purple/red "iron-reactive" color-change wheel cleaners in this catalog. The free acid form is distinct: it is used in some acid wheel-cleaner formulas as a reducing/chelating component rather than as the color-indicator salt, and a visible color-change reaction on brake dust is not guaranteed from the free-acid form alone — confirm against the specific finished product's marketing and independent user reports before describing a product containing it as "color-changing."

Hazard profile

Supplier GHS classifications for the pure substance list Skin Corrosion Category 1B, serious eye damage, Acute Toxicity Category 3 (oral, dermal, and inhalation routes), and Skin Sensitizer 1B. This corrosive/acute-toxic profile is a meaningful driver of DANGER-signal-word classifications in finished acid wheel cleaners that disclose it in SDS Section 3.

Regulatory status

• Not Prop 65 listed (no name or CAS match on the OEHHA list as of the current data pull).
• Confirmed acute aquatic toxicity (Daphnia magna EC50 38 mg/L, 48h; algae EC50 13 mg/L, 72h) with a chronic aquatic hazard Category 3 classification reported by chemical suppliers.
• Readily biodegradable: 67% biodegradation in 28 days (OECD closed-bottle test) and 100% of theoretical BOD in 4 weeks (Japanese MITI test).

Sources

• Supplier SDS/GHS classification data (ECHEMI, ChemicalBook, TCI America, Sigma-Aldrich product listings for CAS 68-11-1).
• OECD closed-bottle and MITI biodegradation study data as reported by chemical suppliers.
• OEHHA Proposition 65 list cross-check (name and CAS, no match).