Thermodynamics of solute transfer from water to hexadecane

Abstract

New measurements of enthalpies of solution in hexadecane and in water (ΔH°_s), and gas-hexadecane Ostwald solubility coefficients (L_H) of neutral monomeric organic solutes are reported. These values, together with literature values of ΔH_s°, L_H, and gas-water Ostwald solubility coefficients (L_w), have been used to derive the Gibbs energies, enthalpies, and entropies of solute transfer from water to hexadecane (ΔG°_tr′, ΔH_tr′°, and ΔS_tr°), as well as water–hexadecane partition coefficients (as log P_H). Results have been examined by the method of multiple linear regression analysis, using the equation, SP =c+dδ₂+sπ₂*+aα₂+bβ₂+vV₂

The sπ₂* term is difficult to interpret, but the aα₂ and bβ₂ terms can be shown to arise through hydrogen bonding of solute molecules to the bulk water that is exothermic but rather disfavoured entropically. It is shown also that thevV₂ term arises due to a combination of cavity effects and general dispersion interactions in bulk water and bulk hexadecane.