A convenient and efficient process for the manufacture of benzenesulfonic acid, 2-((4-amino-3-bromo-9,10-dihydro-9,10-dioxo-1-anthracenyl)amino)-5-methyl monosodium salt (C.I. Acid Blue 78) directly from anthraquinone

C.I. Acid Blue 78 is an important acid dye; its manufacture depends on 1-nitroanthraquinone and all procedures developed for the mononitration of anthraquinone give by-products such as dinitroanthraquinones. This paper presents a new method for the manufacture of C.I. Acid Blue 78 in high yield and good quality. HPLC was used to follow the formation of nitroanthraquinone from anthraquinone, which allowed the nitration of anthraquinone to be stopped at 35–45% conversion to 1-nitroanthraquinone, as the formation of by-products at this point was minimal. At the end of the formation of C.I. Acid Blue 78 from anthraquinone, residual, unreacted anthraquinone was reused for nitration after a single recrystallization stage from acetic acid.