Solvent Red 26

  Solvent Red 26, also known as C.I. 26120, is a purplish red synthetic azo dye. Its chemical formula is C₂₅H₂₂N₄O, or 1-[[2,5-dimethyl-4-[(2-methylphenyl)azo]-phenyl]azo]-2-naphthol. It is soluble in oils and insoluble in water.

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Its main use is as a standard fuel dye in the United States of America mandated by the IRS to distinguish low-taxed heating oil from automotive diesel fuel, and by the EPA to mark fuels with higher sulfur content; it is however increasingly replaced with Solvent Red 164, a similar dye with longer alkyl chains, which is better soluble in hydrocarbons. [1] The concentration required by IRS is a spectral equivalent of 3.9 pounds per 1000 barrels, or 11.13 mg/l, of Solvent Red 26 in solid form; the concentrations required by EPA are roughly 5 times lower.

Its CAS number is [4477-79-6] and its SMILES structure is Oc2ccc1ccccc1c2 N=Nc3cc(C)c(N=N c4ccccc4C)cc3C.

See also Solvent Red 27, Solvent Red 164.