Indigotindisulfonic acid
Indigo carmine (acid form) is a member of the class of indolones obtained by formal 2,2'-oxidative coupling of two molecules of 3-oxo-2,3-dihydroindole-5-sulfonic acids. It has a role as a food colouring and a histological dye. It is a member of indolones, an olefinic compound, an enone, an arenesulfonic acid and a ring assembly. It is a conjugate acid of an indigo carmine(2-).