Comparison between solvatochromic and chromatographic studies of anthraquinones in binary aqueous mixtures

Abstract

The solvatochromic studies on 9,10-anthraquinone (AQ), and its symmetric 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 remarkable 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 components. Moreover, and although stronger dipolar interactions are to be expected between the solute and water, only preferential solvation by the organic solvent is detected in every case. These effects may be explained in terms of self association of water through hydrogen bonding and the “microheterogeneity” of the binary mixtures. Moreover, differences 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 interactions. Reversed-phase liquid Chromatographic (RPLC) studies of AQ and 2,6-DHAQ in aqueous mixtures of methanol, acetonitrile and tetrahydrofuran were also performed. The results were interpreted by the Kamlet-Taft solvatochromic comparison method showing that the solvatochromic results can be correlated with certain success with RPLC data.