Temperature dependence of Henry's law constants and K-OA for simple and heteroatom-substituted PAHs by COSMO-RS

摘要

Henry's Law constants (H) and octanol air partition coefficients (K-OA) for polycyclic aromatic hydrocarbons (PAHs) and selected nitrogen-, oxygen- and sulfur-containing derivatives have been computed using the COSMO-RS method between -5 and 40 degrees C in 5 degrees C intervals. The accuracy of the estimation was assessed by comparison of COSMOtherm values with published experimental temperature-dependence data for these and similar PAHs. COSMOtherm log H estimates with temperature-variation for parent PAHs are shown to have a root-mean-square (RMS) error of 0.38 (PAH), based on available validation data. Estimates of O-, N- and S-substituted derivative log H values are found to have RMS errors of 0.30 at 25 degrees C. Log K-OA estimates with temperature variation from COSMOtherm are shown to be strongly correlated with experimental values for a small set of unsubstituted PAHs, but with a systematic underestimation and associated RMS error of 1.11. Similar RMS error of 1.64 was found for COSMO-RS estimates of a group of critically-evaluated log K-OA, values at room temperature. Validation demonstrates that COSMOtherm estimates of H and K-OA are of sufficient accuracy to be used for property screening and preliminary environmental risk assessment, and perform very well for modeling the influence of temperature on partitioning behavior in the temperature range -5 to 40 degrees C. Temperature-dependent shifts of up to 2 log units in log H and one log unit for log K-OA are predicted for PAH species over the range -5 and 40 degrees C. Within the family of PAH molecules, COSMO-RS is sufficiently accurate to make it useful as a source of estimate for modeling purposes, following corrections for systematic underestimation of K-OA. Average changes in the values for log H and log K-OA, upon substitution are given for various PAH substituent categories, with the most significant shifts being associated with the ionizing nitro functionality and keto groups. (C) 2015 Elsevier Ltd. All rights reserved.