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Para Red

Para Red

IUPAC name	1-[(E)-(4-Nitrophenyl)diazenyl]-2-naphthol
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, paranitraniline red, Pigment Red 1, C.I. 12070, Recolite Para Red B, Carnelio Para Red BS
Identifiers
CAS number	6410-10-2
EINECS number	229-093-8
SMILES	OC1=C(N=NC3=C C=C([N+]([O-])=O) C=C3)C2=C(C=C C=C2)C=C1
Properties
Molecular formula	C₁₆H₁₁N₃O₃
Appearance	Red solid
Melting point	248 - 252 °C
Hazards
R-phrases	R36/37/38
S-phrases	S26, S36
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Para Red (paranitraniline red, Pigment Red 1, C.I. 12070) is a chemical dye. Chemically, the dye is similar to Sudan I. The dye was discovered in 1880 by von Gallois and Ullrich, and was the first azo dye. It dyes cellulose fabrics a brilliant red, but is not very fast. The dye can be washed away easily off of cellulose fabrics if not dyed correctly. Throughout making Para Red, the solution will become acidic and basic. Small amounts of byproducts may be left over after the Para Red dye is made that may be acidic or basic, but if made correctly there are little of these and the byproducts have no effect.

Additional recommended knowledge

Correct Test Weight Handling Guide: 12 Practical Tips

Essential Laboratory Skills Guide

Safe Weighing Range Ensures Accurate Results

Synthesis

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

UK food alert

In the United Kingdom, the dye is not permitted in food. The UK's Food Standards Agency (FSA) stated that "the Agency’s independent scientific experts have advised that, although there are very limited data available, it would be prudent to assume that it could be a genotoxic carcinogen". ^[2]

On 21 April 2005, the FSA announced that some batches of Old El Paso dinner kits had been contaminated with the dye, and issued an alert.^[2] Also, reported on the 5 May 2005, the dye was found in 35 products which have now been taken off supermarket shelves. The products were mainly cooking sauces, though some are also spices.^[3]

References

^ Williamson, Kenneth L. (2002). Macroscale and Microscale Organic Experiments, Fourth Edition. Houghton-Mifflin. ISBN 0618197028.
^ ^a ^b "Old El Paso Dinner Kits for enchiladas and burritos found with illegal dye" (press release), Food Standards Agency, 21 April 2005.
^ "Banned dye found in more products", BBC News, 5 May 2005.