Indian Journal of Chemical Technology Vol. 13, March 2006, pp. 149-155 Densities and ultrasonic velocities of binary mixtures of 2,4,6-trimethyl-1,3,5- trioxane + n-alcohols at 298.15, 303.15 and 308.15 K N N Wankhede, D S Wankhede, M K Lande & B R Arbad * Department of Chemistry, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad 431 004, India Email: abr_chem@yahoo.co.in Received 8 February 2005; revised received 2 November 2005; accepted 10 January 2006 The densities and ultrasonic velocities of binary mixtures of 2,4,6-trimethyl-1,3,5-trioxane + ethanol, 1-propanol and 1- butanol at 298.15, 303.15 and 308.15 K were measured over the whole mole fraction range. Experimental data were used to estimate isentropic compressibility (κ s ), intermolecular free length (L f ), specific acoustic impedance (Z) and their deviations, such as deviation in isentropic compressibility (Δκ s ), excess intermolecular free length (L f E ) and excess acoustic impedance (Z E ). The results are fitted to a Redlich-Kister equation. The results are discussed in terms of molecular interactions. Keywords: Ultrosonic velocities, Binary mixtures, n-Alcohols, 2,4,6-Trimethyl-1,3,5-trioxane IPC Code: B01J19/00 Drug macro-molecular interactions are important phenomenon in physiological media such as blood, membranes and intra and extra cellular fluids 1-3 . In recent years, ultrasonic studies are extensively carried out to measure the thermodynamic properties and predict intermolecular interactions in binary liquid mixtures 4-6 . The sound velocity is one of those physical properties that help in understanding the nature of liquid state. Using the measured values of ultrasonic velocity and density, the thermodynamic properties such as isentropic compressibility (κ s ), intermolecular free length (L f ), specific acoustic impedance (Z) can be computed. 2,4,6-Trimethyl- 1,3,5-trioxane commonly known as paraldehyde is a cyclic trimer of acetaldehyde, is a pharmaceutically important drug as a nervous system depressant and used as a sedative and given to psychiatric patients. Alcohols also find wide applications in pharmaceutical industries. Alcohols are highly self- associated through hydrogen bonding and protic while 2,4,6-trimethyl-1,3,5-trioxane involves weak dipole- dipole interactions. Literature survey reveals that the thermodynamic properties of binary mixtures of 2,4,6-trimethyl-1,3,5-trioxane with n-alcohols have not yet been reported so far hence in order to understand the molecular interactions in the solution phase, a study of measurement of physical properties of 2,4,6-trimethyl-1,3,5-trioxane with n-alcohols was undertaken. In the present paper densities and ultrasonic velocities of binary mixtures of 2,4,6-trimethyl-1,3,5- trioxane + ethanol, 1-propanol and 1-butanol are reported at 298.15, 303.15 and 308.15 K over the entire range of mole fractions. From these experimental values isentropic compressibility (κ s ), intermolecular free length (L f ), specific acoustic impedance (Z) and their deviations such as deviation in isentropic compressibility (Δκ s ), excess intermolecular free length (L f E ) and excess acoustic impedance (Z E ) have been calculated. Experimental Procedure 2,4,6-Trimethyl-1,3,5-trioxane (AR grade) was supplied by Merck and used as such without further purification. Alcohols (Qualigens AR) were refluxed over CaO and distilled at atmospheric pressure. The middle fraction collected of all the liquids were stored over 4 Å type molecular sieve 7,8 . The purity of the purified chemicals was checked by comparing their measured densities and ultrasonic velocities with those reported in the literature 8-10,13 . The experimental and literature values are listed in Table 1. The binary mixtures were prepared by mixing known masses of pure liquids. All measurements of mass were performed on a Mettler one pan balance (E-METTLER, ZURICH) which can read up to fifth place of decimal, with an accuracy of ± 0.05 mg.