Database/Hair Dyeing/Acid Red 18
Mostly natural · ISO 16128

Is Acid Red 18 natural?

Mostly. The dye chromophore is a synthetic azo compound, but its three sodium sulfonate groups count as natural mineral-origin mass under ISO 16128, giving a nonzero index.

INCI nameAcid Red 18
CAS2611-82-7
FormulaC20H11N2Na3O10S3 · 604.5 Da
FunctionHair Dyeing
FeedstockManufactured by diazotising petrochemical naphthylamine/naphthol-sulfonic-acid intermediates and coupling…

How we scored it

3 Na (69 Da) + 3 sulfonate SO3 groups (240 Da) = 309 Da natural mineral mass; aromatic azo/naphthol backbone C20H11N2O (295 Da) petrochemical; 309/604=0.51.
What counts. ISO 16128-2 scores the atoms that remain in the final ingredient. Reagents, solvents, catalysts and protecting groups used during manufacture leave no mass behind and are not counted.

Where it comes from

Manufactured by diazotising petrochemical naphthylamine/naphthol-sulfonic-acid intermediates and coupling them, then neutralising with sodium hydroxide. The aromatic backbone is entirely synthetic; only the sodium and sulfonate mass is mineral in origin.

In plain English

A synthetic red dye used in hair colourants. Most of its structure is man-made, though part of its weight comes from mineral sodium and sulfonate salt groups.

CosIng definition: Acid Red 18 is classed chemically as a monoazo colour. It conforms to the formula:

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Structure

2D structure of Acid Red 18

trisodium;7-hydroxy-8-[(4-sulfonatonaphthalen-1-yl)diazenyl]naphthalene-1,3-disulfonate

PubChem CID 17466 ↗

References

  1. 1ISO 16128-1:2016 and ISO 16128-2:2017 — Guidelines on technical definitions and criteria for natural and organic cosmetic ingredients and products. ISO, Geneva.
  2. 2Acid Red 18. PubChem CID 17466. National Center for Biotechnology Information. pubchem.ncbi.nlm.nih.gov ↗
  3. 3ACID RED 18. CosIng — European Commission cosmetic ingredient database. ec.europa.eu/cosing ↗
  4. 4ACID RED 18. CosIng u2014 European Commission database for information on cosmetic substances and ingredients. https://ec.europa.eu/growth/tools-databases/cosing/search?search=ACID%20RED%2018