Abstract: Solutions of tetraethylammonium phthalate in non-aqueous solvents (ethanol,dimethylsulfoxide, dimethylformamide, and acetonitrile) were studied byelectronic absorption spectroscopy. It was shown that the phthalate aniondimerizes in acetonitrile and dimethylformamide solutions due to π-stacking, theexperimental equilibrium constants being 550±50 and 900±50, respectively.Dimerization of the phthalate anion was not observed in ethanol anddimethylsulfoxide solutions.