Direct Measurements of Vapor Pressures of Chlorinated Paraffin Congeners from Technical Mixtures

Chlorinated Paraffins (CPs) are a complex group of manmade chemicals detected widely in the environment. To predict their environmental fate and effects, it is important to understand their physical-chemical properties including vapor pressure. In this study, the first direct measurements of the vapor pressure for CP congener groups (C_10–16Cl_4–11) are presented. Vapor pressure was measured above three industrial CP mixtures with different congener distributions between 20 and 50°C using a gas saturation method. The measured saturated vapor pressure (P^*) decreased with increasing carbon chain length and Cl content. ΔH_vap ranged between 73 and 122 kJ mol^-1, consistent with data from the literature and model prediction. The experimental log P^* at 25°C agreed well with predictions from an empirical regression model in the literature (R² = 0.97; RSME = 0.25) and with those predicted from the COSMO-RS-trained fragment contribution model (R² = 0.95; RSME = 0.35). A new empirical model was calibrated with the P^* data for 35 congener groups measured in this study. Predicted log P^* values correlate well with field-measured gas/particle partition coefficients and may therefore be used for estimating the environmental fate and pathways of a broad range of CPs in the environment.