SAR/QSAR approaches to solubility, partitioning and sorption of phthalates

The environmental behavior of xenobiotics such as phthalates is closely connected to parameters such as are solubility (Cwsat), partitioning (e.g. Kow) and sorption (e.g. Koc). In this paper the solubility, octanol-water partitioning and sorption of a series of phthalic acid esters are described through various SAR/QSAR concepts including molecular connectivity indices (MCI), electrotopological atomic state indices (EASI) and group-contribution (UNIFAC). Advantages and disadvantages of MCI and UNIFAC based QSARʹs for phthalates are discussed. The water solubility as well as the octanol - water partitioning are satisfactorily calculated by application of UNIFAC-derived activity coefficients. Octanol-water partitioning and sorption, but to a lesser extent solubility are, according to MCI analyses, well correlated to molecular size. Octanol-water partitioning and sorption, but to a lesser extent solubility are, according to EASI analyses, well correlated to hydrophobicity as expressed by the “alkyl- group” electrotopological index. The latter correlations is further improved by introducing the polar component as expressed by the “ester- group” electrotopological index.