Sudan IV

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Sudan IV

Sudan IV (C₂₄H₂₀N₄O) is a lysochrome (fat-soluble dye) diazo dye used for staining of lipids, triglycerides and lipoproteins on frozen paraffin sections. Staining is an important biochemical technique, offering the ability to visually qualify the presence of the fatty compound of interest without isolating it. It has the appearance of reddish brown crystals with melting point 199 °C and maximum absorption at 520(357) nm.

Sudan IV is one of the dyes used for Sudan staining. Similar dyes include Oil Red O, Sudan III, and Sudan Black B.

Its CAS number is [85-83-6] and its SMILES structure is OC1=C(N=NC3=CC=C (N=NC4=CC=CC=C4C) C=C3C)C2=C (C=CC=C2)C=C1.

Its risk and safety phrases are R36/R38 and S26.

Its other names are Sudan R, C.I. Solvent Red 24, C.I. 26105, Lipid Crimson, Oil Red, Oil Red BB, Fat Red B, Oil Red IV, Scarlet Red, Scarlet Red N.F, Scarlet Red Scharlach, and Scarlet R. Its purified form is called Biebrich scarlet R, which should not be confused with the water-soluble Biebrich scarlet.

In industry, it is used to color nonpolar substances like oils, fats, waxes, greases, various hydrocarbon products, and acrylic emulsions.

Sudan IV is also used in United Kingdom as a fuel dye to dye lower-taxed heating oil; because of that it is also known as Oil Tax Red.

As a food dye, Sudan IV is considered an illegal dye, mainly because of its harmful effect over a long period of time. It was ruled unsafe in the 1995 food safety regulations report.