Thermodynamics of transfer of naphthalene and 2-naphthoic acid from water to (water plus ethanol) mixtures at T=298.15 K

Standard thermodynamic functions of transfer of naphthalene and 2-naphthoic acid from water to (water + ethanol) mixtures at T = 298.15 K have been determined from solubility measurements at different temperatures. Standard free energies of transfer of both naphthalene and 2-naphthoic acid showed decreasing tendency with the increasing x(EtOH), and the standard entropy and enthalpy of transfer exhibited a change of double peaks with x(EtOH). The Delta(Tr)G(0) of 2-naphthoic acid decreased more rapidly than that of naphthalene when x(EtOH) < 0.746 and lower than that of naphthalene when x(EtOH) >0.746 at T = 298.15 K. The double peaks in the curves of standard entropy and enthalpy of transfer illustrated that the microstructure of the series of mixed solvents of (water + ethanol) underwent a variable process from ordered to disordered and then from disordered to ordered. The results mean that there is a relatively ordered structure near x(EtOH) = 0.13 in the (water + ethanol) solutions besides the existence of a clathrate structure in the water-rich region. (C) 2003 Elsevier Science Ltd. All rights reserved.