D&C RED NO. 40 or CI 16035 is a synthetic chemical, azo derivative, water-soluble dye, referred to by many synonyms, of which the most common is Allura Red 40 or Allura Red AC and is among the most widely used dyes in the world. 

The name describes the structure of the molecule:

• CI: Color Index, a reference database managed by the Society of Dyers and Colourists and the American Association of Textile Chemists and Colorists. The color index assigns unique numbers to each dye or pigment.
• 16035:  the specific number assigned to a synthetic red dye known as Allura Red AC,  Food Red 17, C.I. Acid Red 18 and FD&C Red 40.

The synthesis process takes place in different steps:

• Preparation. The synthesis of FD&C Red 40 begins with the preparation of the necessary raw materials. This typically includes naphthalene, which is a polycyclic aromatic hydrocarbon, and other chemicals.
• Sulphonation. Naphthalene undergoes a process called sulfonation, in which a group of sulfuric acid is added to the naphthalene molecule.
• Diazotization and coupling. Naphthalene sulfonate and diazotized, a procedure that involves replacing an amino group with a diazo group. This is followed by a coupling reaction, where diazo is combined with another molecule to form the azo dye.
• Purification. This is the final stage of the synthesis process and involves the removal of any raw materials and by-products not reacted by the reaction mixture to obtain the pure FD&C Red 40.

It occurs as a fine red powder. Soluble in water and ethanol.

It contains the azo group, which is the largest group of colours and accounts for more than half of global colour production. In food it is labelled as E129 on the European Food Additives List and is subject to an Acceptable Daily Intake of 0.7 mg/kg body weight (1).

Industrial dyes, which are used to colour food, drink, meat, sweets, hair dyes, face and body care cosmetics, fall into two categories: 

• natural compounds or additives derived from the natural ingredient (i)
• synthetic chemicals (ii)

Safety

Some countries have regulated and, in some cases, banned the use of Allura red in food and beverages.  It's approved for use in the EU, US, and many other countries, although there have been concerns about its potential to cause allergic reactions and its safety has been the subject of debate.

There is no consensus in the scientific literature that Allura Red is genotoxic. In vivo tests on laboratory animals have provided conflicting results (2).

CI 16035 Allura red studies

Optimal typical characteristics of the commercial product Allura Red

• Molecular Formula : C₁₈H₁₄N₂Na₂O₈S₂
• Molecular Weight : 496.42
• Exact mass  495.998688
• CAS : 25956-17-6
• UNII WZB9127XOA
• EC Number 247-368-0
• DSSTox Substance ID DTXSID4024436
• MDL number  MFCD00059526
• PubChem Substance ID 24869338
• InChI=1S/C18H16N2O8S2.2Na/c1-10-7-14(16(28-2)9-17(10)30(25,26)27)19-20-18-13-5-4-12(29(22,23)24)8-11(13)3-6-15(18)21;;/h3-9,21H,1-2H3,(H,22,23,24)(H,25,26,27);;/q;2*+1/p-2  
• InChl Key      CEZCCHQBSQPRMU-UHFFFAOYSA-L
• SMILES    CC1=CC(=C(C=C1S(=O)(=O)[O-])OC)N=NC2=C(C=CC3=C2C=CC(=C3)S(=O)(=O)[O-])O.[Na+].[Na+]
• IUPAC   disodium;6-hydroxy-5-[(2-methoxy-5-methyl-4-sulfonatophenyl)diazenyl]naphthalene-2-sulfonate
• ChEBI  172687
• NACRES  NA.47

Synonyms :

• Allura Red AC
• Allura Red 40
• FDC Red 40
• Red No. 40
• Allura red AC dye
• C.I. Food Red 17
• Food red 17
• Food Red No. 40
• FD&C Red No. 40
• Disodium 6-hydroxy-5-((6-methoxy-4-sulfo-m-tolyl)azo)-2-naphthalenesulfonate
• 2-Naphthalenesulfonic acid, 6-hydroxy-5-((6-methoxy-4-sulfo-m-tolyl)azo)-, disodium salt
• Disodium 6-hydroxy-5-((2-methoxy-5-methyl-4-sulfophenyl)azo)-2-naphthalenesulfonate

References________________________________________________________________________

(1) Rovina K, Siddiquee S, Shaarani SM. Extraction, Analytical and Advanced Methods for Detection of Allura Red AC (E129) in Food and Beverages Products. Front Microbiol. 2016 May 27;7:798. doi: 10.3389/fmicb.2016.00798.

(2) Tsuda S, Murakami M, Matsusaka N, Kano K, Taniguchi K, Sasaki YF. DNA damage induced by red food dyes orally administered to pregnant and male mice. Toxicol Sci. 2001 May;61(1):92-9. doi: 10.1093/toxsci/61.1.92.

Ferrer Amate C, Unterluggauer H, Fischer RJ, Fernández-Alba AR, Masselter S. Development and validation of a LC-MS/MS method for the simultaneous determination of aflatoxins, dyes and pesticides in spices. Anal Bioanal Chem. 2010 May;397(1):93-107. doi: 10.1007/s00216-010-3526-x.

Honma M. Evaluation of the in vivo genotoxicity of Allura Red AC (Food Red No. 40). Food Chem Toxicol. 2015 Oct;84:270-5. doi: 10.1016/j.fct.2015.09.007.