Spectrophotometric studies of acidity constant and Cu2+ ion complexation of 1-hydroxy-2-(prop-2 '-enyl)-4-(prop-2 '-enyloxy)-9,10-anthraquinone in methanol-water mixtures

The acidity constant of 1-hydroxy-2-(prop-2'-enyl)-4-(prop-2'-enyloxy)-9,10 -anthraquinone in different methanol-water mixtures at 25 degreesC has been determined spectrophotometrically. A linear reverse relationship is observ ed between tile pK(a) and mole fraction of methanol in the solvent mixtures . Tile complexation reaction between the anthraquinone derivative used and Cu2+ ion has been studied in methanol solution at 25 degreesC by a spectrop hotometric technique. The stoichiometry of tile resulting complex was found to be 1:1. The formation constant of the Cu2+-anthraquinone complex, evalu ated from the computer fitting of the absorbance-mole ratio data at 5 diffe rent wavelengths, is log K-f = 4.59 +/- 0.06.