Predicting Partition Coefficients of Short-Chain Chlorinated Paraffin Congeners by COSMO-RS-Trained Fragment Contribution Models

Chlorinated paraffins (CPs) are highly complex mixtures of polychlorinated n-alkanes with differing chain lengths and chlorination patterns. Knowledge on physicochemical properties of individual congeners is limited but needed to understand their environmental fate and potential risks. This work uses a sophisticated but time-demanding quantum chemically based method COSMO-RS and a fast-running fragment contribution approach to enable prediction of partition coefficients for a large number of short-chain chlorinated paraffin (SCCP) congeners. Fragment contribution models (FCMs) were developed using molecular fragments with a length of up to C₄ in CP molecules as explanatory variables and COSMO-RS-calculated partition coefficients as training data. The resulting FCMs can quickly provide COSMO-RS predictions for octanol–water (K_ow), air–water (K_aw), and octanol–air (K_oa) partition coefficients of SCCP congeners with an accuracy of 0.1–0.3 log units root mean squared errors. The FCM predictions for K_ow agree with experimental values for individual constitutional isomers within 1 log unit. The distribution of partition coefficients for each SCCP congener group was computed, which successfully reproduced experimental log K_ow ranges of industrial CP mixtures. As an application of the developed FCMs, the predicted K_aw and K_oa were plotted to evaluate the bioaccumulation potential of each SCCP congener group.