Comparative solubility investigations of anthraquinone disperse dyes in near- and supercritical fluids

The present study covers equilibrium solubilities of a homologous series of 1,4-bis-(alkylamino)-9,10-anthraquinones (with alkyl from methyl to octadecyl) and additionally of the more polar anthraquinone derivatives 1-amino-4-hydroxy-2-phenoxy-9,10-anthraquinone (C. I. Disperse Red 60) and 1,4-diamino-2-methoxy-9,10-anthraquinone (C. I. Disperse Red 11) in several near- and supercritical fluids. The solubilities of the 1,4-bis-(alkylamino)-substituted anthraquinones except the octadecyl-derivative were measured by means of a supercritical fluid chromatograph (SFC) between 299 and 346 K and up to a maximum pressure of 20 MPa. On the contrary, the measurements of 1,4-bis-(octadecylamino)-9,10-anthraquinone as well the two Disperse Red representatives 60 and 11 were performed using a static optical high-pressure autoclave within pressures from 7 to 180 MPa and temperatures up to 400 K. We reflected on the results from three different points of view, namely the influence of different substituents, of the particular solid state, and of different solvent gases. A complex pattern of interrelations of these parameters determining equilibrium solubilities opened; decoupling and a separate view proved to be insufficient.