Anthraquinone dyes

[3] One of the most important anthraquinone dyes of herbal origin is alizarin, which is extracted from the dyer's madder (Rubia tinctorum).

Because demand for red dyes is predicted to increase, researchers are exploring metabolic engineering approaches for the production of synthetic carminic acid.

Aminoanthraquinone (4) is thus accessible by reaction of anthraquinone sulfonic acid with ammonia or by reduction of nitroanthraquinone.

By replacing the bromine substituent with an aliphatic or aromatic amine, vibrant blue dyes are obtained.

Vat Blue 4) - the synthesis of which was developed by René Bohn in 1901: By dimerization of 2-aminoanthraquinone (1) under strongly alkaline conditions at 220-235 °C, intermediate stage 3 is obtained in two steps, which is cyclized intramolecularly and oxidized to indanthrone 5.