Chrysoine resorcinol

Chrysoine resorcinol is a synthetic azo dye which was formerly used as a food additive. In Europe, it was banned as a food additive in 1977. In the US, it was banned in 1988.

Chrysoine resorcinol can be used as a pH indicator with a color change between pH 11 and pH 12.7. In colorimetry, it has an absorption maximum of 387 nm.

Preparation
Acid orange 6 can be synthesised via the azo coupling of sulfanilic acid and resorcinol,