isopurpurin

Century Dictionary and Cyclopedia

1. n. A coal-tar color (C₁₄H₅O₂(OH)₃) used in dyeing, closely allied to alizarin, formed by heating beta-anthraquinon disulphonic acid with caustic soda and potassium chlorate. It is sold in commerce under the name of alizarin, and produces the yellow shade of red, while true alizarin gives bluish shades of red. Also called anthrapurpurin.

Wiktionary

1. n. organic chemistry 1,2,7-trihydroxyanthraquinone