Thermodynamic study of the partitioning of organic compounds between water and octan-1-ol. Effects of water as cosolvent in the organic phase

The effect of water, as cosolvent, in changing the affinity of octan-1-ol towards organic solutes according to their chemical nature, has been examined by determining the thermodynamic functions of solvation, ΔsolvX°(j)(X=G, H, S), in anhydrous (j= oct) and in water-saturated octan-1-ol (j= oct*) of organic compounds of the RY type (R = hydrocarbon frame, Y = H, O, CO, NH2, NH, N). From these data and the analogous thermodynamic functions of hydration, ΔsolvX°(W), the thermodynamic functions, ΔtrX°(j→j*), for the three ideal or practical processes of transfer (namely, w→oct, w→oct*, oct→oct*) have been calculated.The ΔtrX°(j→j*) functions have been correlated with the structure of the solutes by using their intrinsic volume as a unique structural parameter. The coefficients of the linear equations obtained give information about the contributions to the envisaged thermodynamic function, connected with the formation of a cavity containing the solute and to the solute–solvent interactions. In the case of the ΔtrG°(j→j*) functions, the LSERs (linear solvation energy relationships) have also been used for correlating the thermodynamic functions to the structural features of the solutes.