Solubility and preferential solvation of benzocaine in {methanol (1) + water (2)} mixtures at 298.15 K

The equilibrium solubility of benzocaine (BZC) in several {methanol (1) + water (2)} mixtures at 298.15K was determined. Solubility values are expressed in mole fraction and molarity and were calculated with the Jouyban-Acree model. Preferential solvation parameters of BZC by methanol (x(1,3)) were derived from their thermodynamic solution properties using the inverse Kirkwood-Buff integrals method. x(1,3) values are negative in water-rich mixtures (0.00<x(1)<0.32) but positive in the other mixtures (0.32 < x(1)<1.00). To explain the preferential solvation by water in the former case, it is conjecturable that the hydrophobic hydration around non-polar groups of BZC plays a relevant role in the solvation. Moreover, the higher solvation by methanol in mixtures of similar cosolvent compositions and methanol-rich mixtures could be explained in terms of the higher basic behaviour of methanol regarding water.