(750j) Improved Directional Hydrogen Bonding Interactions for the COSMO-SAC Model for Prediction of Activity Coefficients

A Novel Approach for the Determination of Directional
Hydrogen Bonding Interactions for the COSMO-SAC Model based on Molecular
Electrostatic Potentials

Chun-Kai
Chang ^a, Wei-Lin Chen ^b, David T. Wu ^c and Shiang-Tai
Lin ^a*

^a Department of
Chemical Engineering, National Taiwan University, Taiwan

^b Daxin Materials
Corporation, Taiwan

^c Department of
Chemistry and Department of Chemical and Biological Engineering, Colorado
School of Mines, Golden, CO, USA

ABSTRACT

The COSMO-SAC model is a powerful tool for
predicting the phase behavior of liquids based on quantum chemical calculations
of molecules solvated in a medium of infinite dielectric constant. However, many
studies have shown that its accuracy is reduced for
mixtures containing hydrogen bonding species. Therefore, there has been a
continuous effort to improve the description of hydrogen bonding interactions. In
a recent work, Chen and Lin showed that the consideration of directional
hydrogen bonding in the COSMO-SAC model significantly improves the description
of properties of associating fluids (Phys. Chem. Chem. Phys., 2017, 19,
20367-20376). In their method, the direction of a hydrogen bond was determined
based on the VSEPR theory; however, this geometric approach does not reflect
the local electronic environment of the lone pairs and cannot be unambiguously applied
to certain molecules such as CO₂ and HF. In this work, we adopt a
new scheme that determines the hydrogen bond acceptors of a molecule based on
the minima of the molecular electrostatic potential (MESP) instead of the
molecular geometry and bonding assignment. This method is applicable for all
types of compounds as the needed electrostatic potential can be obtained from
quantum chemical calculations. In this work, we compare the performance of the
newly proposed method, referred to as COSMO-SAC(DHB)/MESP, to the VSEPR based
method, denoted as COSMO-SAC(DHB)/VSEPR, and the original COSMO-SAC(2002) and
revised COSMO-SAC(2010) models. The data considered include vapor-liquid
equilibrium (VLE) of 586 binary pairs, liquid-liquid equilibrium (LLE) of 190
binary pairs, 431 infinite dilution activity coefficients (IDAC) and 291 octanol-water
partition coefficients (K_ow). It is shown that the directional
hydrogen bond interactions determined based on the MESP provides the best overall
accuracy for the systems studied.

Keywords: COSMO-SAC, Directional Hydrogen
Bond, Molecular Electrostatic Potential.