Towards methods for facile estimation of enthalpies of vaporization of neutral organic chemicals using the principles of linear free energy relationship

Abstract

Recently, research interest is revolving in understanding the temperature dependence of environmental partitioning properties governing the fate, behavior, and transport of organic pollutants, which may be attributed to the global warming phenomenon. The environmental partitioning property data are generally measured at room temperature (20-25◦C) which requires the temperature correction for the hot climatic regions. Enthalpy is an important thermodynamic parameter required to correct partitioning property data for temperatures differences. In this thesis, I developed an easy and parsimonious 2-parameter partitioning model (2p-PM) to predict standard molar enthalpies of vaporization. Unlike previous models such as the widely used Abraham Solvation Model (ASM), my 2p-PM — based on correlation of enthalpy of vaporization with a linear combination of two partition coefficients of octanol-water and air-water systems — is computationally fast and parametrically parsimonious with almost similar predictive performance as observed for the ASM. This new model can be integrated in the US EPA’s EPI-Suite Software. In the second part of my thesis, I developed a GC×GC model which is based on the retention time information of non-polar chemicals on the comprehensive two-dimensional gas chromatography (GC×GC). It can be applied to complex environmental mixtures such as polyhalogenated flame retardants, paint additives, and plasticizers. Taken together, this study provides the means and methods to understand the temperature dependence of vaporization of chemicals in different climatic scenarios.