Tautomeric composition and tautomeric transformation sequence of 1,4-bis(alkylamino)anthraquinones

Compounds widely known as 1,4-bis(alkylamino)-9,10-anthraquinones are in fact neither individual substances nor substituted 9,10-anthraquinones but equilibrium mixtures of tautomers. Their aminoimine tautomeric transformations follow the sequence 4,9-bis(alkylamino)-1,10-anthraquinones ? 9-alkylamino-4-(alkylimino)-10-hydroxy-1,4-dihydroanthracen-1-ones ? N ¹,N ¹⁰-dialkyl-4,9-dihydroxy-1,10-dihydroanthracene-1,10-diimines.