Partitioning of Solutes in Different Solvent Systems: The Contribution of Hydrogen-Bonding Capacity and Polarity

Abstract

Published partition coefficient values of 121 solutes in five solvent systems (1-octanol-water, n-heptane-water, chloroform-water, diethyl ether-water, and n-butyl acetate-water) were correlated with solute properties, namely intrinsic molecular volume (indicator of cavity formation) and the solvatochromic parameters (dipolarity/ polarizability), p (H-bond acceptor basicity), and a (H-bond donor acidity). While the cavity term and the H-bond accepting capacity played a comparable role in all solvent systems, the H-bond donor acidity was significant only in the alkane-water and chloroform-water systems. Comparison of the regression coefficients of if", /3, and a demonstrated the important role that water content at saturation in the organic solvents plays in the partitioning of solutes. Analysis of the differences between 1-octanol-water and n-heptane-water partition coefficients (Alog P. hep) and between 1 octanol-water and chloroform-water partition coefficients (Alog Poct-cm) showed that these values mainly quantitate the capacity of solute to donate hydrogen bonds. In contrast, the differences between 1-octanol-water and diethyl ether-water or n-butylacetate- water partition coefficients, (Alog Poc and Alog Poct-ba. respectively) contain no structural information.