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    Equilibrium solubility of vanillin in some (ethanol plus water) mixtures: determination, correlation, thermodynamics and preferential solvation
    (Elsevier, 2021) Akay, Sema; Kayan, Berkant; Jouyban, Abolghasem; Martinez, Fleming; Acree, William E., Jr.
    Equilibrium mole fraction solubility of vanillin in nine aqueous-ethanolic mixtures, as well as in neat water and neat ethanol, was determined at seven temperatures from T = 293.15 to T = 323.15 K. Vanillin solubility in these mixtures was adequately correlated with several well-known correlation models with the mean percentage deviations of 5.9 to 18.3%. Respective apparent thermodynamic functions, i.e. Gibbs energy, enthalpy, and entropy, for the dissolution, mixing and solvation processes, were computed using the van't Hoff and Gibbs equations. The enthalpy-entropy relationship for vanillin was non-linear in the plot of enthalpy vs. Gibbs energy of dissolution with positive slopes from neat water to the mixture of w(1) = 0.10 and the interval 0.50 < w(1) < 0.90 but negative in the interval 0.10 < w(1) < 0.50 and from w(1) = 0.90 to neat ethanol. Accordingly, in the first cases the vanillin transfer from more polar to less polar solvent systems is enthalpy-driven but entropy-driven for the last ones. Moreover, by means of the inverse Kirkwood-Buff integrals is observed that vanillin is preferentially solvated by water molecules in water-rich mixtures but preferentially solvated by ethanol molecules in mixtures of 0.23 < x(1) < 1.00.