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Annex II Entry 9 17/10/2010

Thyropropic acid (INN) and its salts

Thyropropic acid (INN) and its salts is listed in Annex II as a prohibited substance for cosmetic products placed on the EU market.

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Prohibited substance— Annex II, EU Regulation 1223/2009
Entry: 9

Chemical identity and properties

PubChem 2D chemical structure for CAS 51-26-3
CAS 51-26-3PubChem CID 5804

3,3',5-Triiodothyropropionic acid

Thyropropic acid is an aromatic ether. — ChEBI

IUPAC name
3-[4-(4-hydroxy-3-iodophenoxy)-3,5-diiodophenyl]propanoic acid
Molecular formula
C15H11I3O4
Molecular weight
635.96 g/mol
Exact mass
635.7792 Da
XLogP3
4.8
Topological polar surface area
66.8 Ų
Hydrogen-bond donors
2
Hydrogen-bond acceptors
4
Covalent units
1
Defined stereocentres
0

Also known as

4-(4-Hydroxy-3-iodophenoxy)-3,5-diiodobenzenepropanoic acidRefChem:910529THYROPROPIC ACID3,3',5-Triiodo Thyropropionic AcidAcido tiropropicoTriopron; TripropAcide thyropropiqueThyropropic acid [INN]
16 more reported names
3-(4-(4-hydroxy-3-iodophenoxy)-3,5-diiodophenyl)propanoic acidLevothyroxine Impurity 19OK7481S22O4-(4-Hydroxy-3-iodophenoxy)-3,5-diiodohydrocinnamic acid3-[4-(4-hydroxy-3-iodo-phenoxy)-3,5-diiodo-phenyl]propanoic acidAcidum thyropropicumUNII-OK7481S22OAcido tiropropico [INN-Spanish]Acide thyropropique [INN-French]Acidum thyropropicum [INN-Latin]Benzenepropanoic acid, 4-(4-hydroxy-3-iodophenoxy)-3,5-diiodo-C15H11I3O4cid_5804triiodothyropropionic acid, 5THYROPROPIC ACID [MI]CHEBI:135860
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External database identifiers

Retrieved from NIH PubChem on 2026-08-31 by checksum-valid CAS matching. Chemical properties do not replace the regulatory decision on this page.

Record details

Chemical name

Thyropropic acid (INN) and its salts

Chemical / IUPAC name

4-(4-Hydroxy-3-iodophenoxy)-3,5-diiodobenzenepropanoic acid

Regulatory information

Regulation

(EC) 2009/1223

See every entry this act set

Key data

CAS
51-26-3
EC
—
Annex
II
Entry number
9

Direct matches are limited for this record, so nearby entries from Annex II are shown as well.

What Annex II means for Thyropropic acid (INN) and its salts

Thyropropic acid (INN) and its salts is listed as a prohibited substance under Annex II of EU Cosmetics Regulation 1223/2009 and must not be intentionally added. Article 17 separately addresses unintended small quantities that are technically unavoidable under good manufacturing practice and compatible with the Article 3 safety requirement.

Formulators must screen their ingredients and raw materials to ensure none contain this substance. Suppliers should provide documentation confirming absence when requested.

The page also surfaces 12 related annex records with overlapping identifiers, annex logic or naming patterns.

Compliance checklist

  • Verify this substance is absent from all raw materials and finished formulations.
  • Request absence confirmation or CoA from raw material suppliers.
  • Document the screening result in the Product Information File (PIF).

Frequently asked questions

Yes. Thyropropic acid (INN) and its salts is listed in Annex II of EU Cosmetics Regulation 1223/2009 and is prohibited as an intentionally added cosmetic ingredient. Article 17 provides a narrow exception for unintended small quantities that are technically unavoidable under good manufacturing practice, provided the product remains safe under Article 3.

CAS 51-26-3 is the unique numerical identifier assigned to Thyropropic acid (INN) and its salts by the Chemical Abstracts Service. In cosmetic compliance work, the CAS number is used to cross-reference the substance across regulatory databases, raw material specifications and safety assessment reports. Multiple EU annex entries may share the same CAS number if the same substance appears under different conditions or in different annexes.

Use the INCI Checker tool on this site to paste your full ingredient list (INCI) and scan it against all Annex II–VI entries. The tool highlights any ingredients that match restricted, prohibited or allergen-flagged records. This is useful for rapid compliance screening of finished product formulas or raw material declarations.
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Source note for Annex II record Thyropropic acid (INN) and its salts

This page summarizes one Annex II record for Thyropropic acid (INN) and its salts from public European Commission cosmetic materials and adds linked inventory or identifier matches when available.

Use this record page to review Annex II conditions for Thyropropic acid (INN) and its salts, but confirm any final regulatory decision against the current official annex wording and source files.

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