Ultrasonic Speed and Related Thermo-acoustical Parameters of Solutions of 1,1'-Bis(3-methyl-4-ethoxyacetylphenoxy)cyclohexane at Four Different Temperatures

The density (rho), viscosity (eta) and ultrasonic speed (U) of the pure solvents: 1,4-dioxane (DO), ethyl acetate (EA), tetrahydrofuran (THF) and solutions of the biologically active 1,1'-bis(3-methyl-4-ethoxyacetylphenoxy)cyclohexane were investigated at four temperatures: 298, 303, 308 and 313 K over a wide range of concentrations (0.1-0.01 mol center dot dm(-3)) to understand molecular interactions in these solutions. Various acoustical and thermodynamic parameters such as specific acoustical impedance (Z), isentropic (adiabatic) compressibility (kappa (S) ), Rao's molar sound function (R (m)), van der Waals constant (b), internal pressure (pi), free volume (V (f)), intermolecular free path length (L (f)), classical absorption coefficient {(alpha/f (2))(Cl)}, viscous relaxation time (tau), Gibbs energy of activation (Delta G*), enthalpy of activation (Delta H*) and entropy of activation (Delta S*) were determined using the rho, eta and U data. A good to excellent correlation between a given parameter and concentration (C) is observed at all temperatures (T) and solvent systems studied. A linear increase or decrease of acoustical and thermodynamic parameters with concentration and temperature indicate the presence of strong molecular interactions in the solutions. Delta G* decreases linearly with increasing concentration and temperature in the DO system, while it decreases with C and increases with temperature in the EA and THF systems. The enthalpy of activation (Delta H*) was found to be practically independent of concentration but Delta H* and Delta S* were found to be slightly concentration dependent. In the DO system they are positive, while in the EA and THF systems they are negative.