Para red

Para red (paranitraniline red, Pigment Red 1, C.I. 12070) is a dye. Chemically, it is similar to Sudan I. It was discovered in 1880 by von Gallois and Ullrich and was the first azo dye. It dyes cellulose fabrics a brilliant red color, but is not very fast. The dye can be washed away easily from cellulose fabrics if not dyed correctly. Acidic and basic stages both occur during the standard formation of Para Red, and acidic or basic byproducts may be present in the final product.

Para red
Names
Preferred IUPAC name
1-[(E)-(4-Nitrophenyl)diazenyl]naphthalen-2-ol
Other names
1-[(4-Nitrophenyl)azo]-2-naphthalenol, 1-((4-nitrophenyl)azo)-2-naphthol, 1-[(p-nitrophenyl)azo]-2-naphthalenol, 1-[(p-nitrophenyl)azo]-2-naphthol, 1-[(E)-(4-Nitrophenyl)diazenyl]-2-naphthol, paranitraniline red, Pigment Red 1, C.I. 12070, Recolite Para Red B, Carnelio Para Red BS
Identifiers
3D model (JSmol)
ChEMBL
ChemSpider
ECHA InfoCard 100.026.449
EC Number
  • 229-093-8
UNII
  • InChI=1S/C16H11N3O3/c20-15-10-5-11-3-1-2-4-14(11)16(15)18-17-12-6-8-13(9-7-12)19(21)22/h1-10,20H/b18-17+ checkY
    Key: WOTPFVNWMLFMFW-ISLYRVAYSA-N checkY
  • InChI=1/C16H11N3O3/c20-15-10-5-11-3-1-2-4-14(11)16(15)18-17-12-6-8-13(9-7-12)19(21)22/h1-10,20H/b18-17+
    Key: WOTPFVNWMLFMFW-ISLYRVAYBR
  • O=N(=O)c1ccc(cc1)/N=N/c2c3ccccc3ccc2O
Properties
C16H11N3O3
Molar mass 293.282 g·mol−1
Appearance Red solid
Melting point 248 to 252 °C (478 to 486 °F; 521 to 525 K)
Hazards
GHS labelling:
GHS07: Exclamation mark
Warning
H315, H319, H335
P261, P264, P271, P280, P302+P352, P304+P340, P305+P351+P338, P312, P321, P332+P313, P337+P313, P362, P403+P233, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Synthesis

Para red is prepared by diazotization of para-nitroaniline at ice-cold temperatures, followed by coupling with β-naphthol:[1]

Synthesis of Para Red
Synthesis of Para Red

Regulation

Para red is not approved for use in food in any jurisdiction. In 2005, Old El Paso dinner kits were found to be contaminated with the dye and removed from supermarket shelves.[2][3]

References
  1. Williamson, Kenneth L. (2002). Macroscale and Microscale Organic Experiments, Fourth Edition. Houghton-Mifflin. ISBN 0-618-19702-8.
  2. "Old El Paso Dinner Kits for enchiladas and burritos found with illegal dye" (press release). Food Standards Agency. 21 April 2005.
  3. "Banned dye found in more products". BBC News. 5 May 2005.
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