Beta naphthol pigments
Description
A general class of azo-type organic colorants that are based on β-naphthol (2-naphthol), more specifically, on 1-arylhydrazone-2-naphthol. The beta-naphthol molecules are made into colored pigments or dyes by two different processes. Some pigments are made by coupling the beta-naphthol with a substituted aniline. Other solvent-soluble dyes are made by coupling the beta-naphthol with a sulfonate or carboxylate group to produce an ion, which is then metallized. Both types of dyes are traditionally known as Sudan dyes.
Synonyms and Related Terms
2-naphthol dyes; β-naphthol; naphthalen-2-ol (IUPAC); 2-Hydroxynaphthalene; 2-Naphthalenol; beta-Naphthol; Naphth-2-ol; 2-naphthol derived dyes; dinitroaniline; orthonitroaniline
Tables
β-naphthol Pigment Group:
| Pigment number | Pigment name | Dates | Properties | Uses |
|---|---|---|---|---|
| PO5 | Dinitroaniline Orange, Orthonitroaniline orange, Hansa Orange | first prepared 1895; patented 1909; introduced to US in 1940s | Intense color, but tends to darken | printing inks, architectural paint, artist paints, color plastics |
| PR1 | Para red | first synthesized azo red; made in 1895 | Good chemical resistant but poor lightfastness, as well as poor bleed and heat resistance | Rarely used now, previously used for industrial finishes and printing |
| PR3 | Toluidine red | synthesized in 1905 | Height of popularity in 1970s, decreasing since due to poor lightfastness | wax crayons, pastels, watercolors |
| PR4 | Chlorinated para red | prepared in 1907 | Poor lightfastness and poor bleed resistance | wax crayons, colored pencils, artists color |
| PR6 | Parachlor red | discovered 1906 | Better lightfastness but poor bleed resistance | used in latex paints and outdoor signs |
See also Naphthol pigments.
Physical and Chemical Properties
- Many beta-naphthol pigments are fluorescent
Resources and Citations
- Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
- Hoechst Celanese Corporation, Dictionary of Fiber & Textile Technology (older version called Man-made Fiber and Textile Dictionary, 1965), Hoechst Celanese Corporation, Charlotte NC, 1990
- Rosalie Rosso King, Textile Identification, Conservation, and Preservation, Noyes Publications, Park Ridge, NJ, 1985
- Fairchild's Dictionary of Textiles, Phyllis G.Tortora, Robert S. Merkel (eds.), Fairchild Publications, New York City, 7th edition, 1996
- Encyclopedia Britannica, http://www.britannica.com Comment: "Chemical Compound." (Accessed 13 May 2004). gives date of first use as 1912
- B. Berrie, S.Q. Lomax, 'Azo Pigments: Their History, Synthesis, Properties and Use in Artists' Materials', Studies in the History of Art , National Gallery of Art, Washington DC, No. 57, 1997 Comment: patented 1911
- Wikipedia: 2-Napthol Accessed Apr. 2026