COMPARISON BETWEEN SOLVATOCHROMIC AND CHROMATOGRAPHIC STUDIES OF ANTHRAQUINONES IN BINARY AQUEOUS MIXTURES

The solvatochromic studies on 9,10-anthraquinone (AQ), and its symmetr ic dihydroxy derivatives namely 1,5-dihydroxyanthraquinone (1,5-DHAQ) and 2,6-dihydroxyanthraquinone (2,6-DHAQ) in aqueous solvent mixtures of methanol, acetonitrile, tetrahydrofuran and n-propanol are reported . Preferential solvation is detected in every case. However, a remarka ble variation in the magnitude of the preferential solvation constant K-AB is observed when the composition of the mixture is changed. This effect is attributed to the solvent-solvent interaction between compon ents. Moreover, and although stronger dipolar interactions are to be e xpected between the solute and water, only preferential solvation by t he organic solvent is detected in every case. These effects may be exp lained in terms of self association of water through hydrogen bonding and the ''microheterogeneity'' of the binary mixtures. Moreover, diffe rences are observed in the solvatochromic behavior of the solutes. In the case of 2,6-DHAQ the so-called synergistic effect is observed and explained as a function of the strong hydrogen bond solute-solvents in teractions. Reversed-phase liquid chromatographic (RPLC) studies of AQ and 2,6-DHAQ in aqueous mixtures of methanol, acetonitrile and tetrah ydrofuran were also performed. The results were interpreted by the Kam let-Taft solvatochromic comparison method showing that the solvatochro mic results can be correlated with certain success with RPLC data.