ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2014, Vol. 88, No. 4, pp. 601–606. © Pleiades Publishing, Ltd., 2014. 601 1 INTRODUCTION Ultrasonic technique is one of the sensitive meth- ods of elucidation of the molecular interactions between polar and non polar components. Such stud- ies in liquid mixtures have great relevance in many fields of applied and theoretical research [1–5]. Methyl formate is an ester. It is used in the lacquer industry as a solvent for cellulose nitrate. It is also used as a fumigant and larvacide for tobacco. The molecular interaction studies of liquid mixtures with alcohols as one of the components is of particular interest, since alcohols are highly polar and self associ- ated through hydrogen bonding in pure state [6–8]. Excess molar enthalpies of ethyl formate and 1-pro- panol, 2-propanol, 1-butanol, and 2-butanol, and 1-pentanol at 308.15 K were reported by Dong et al [9]. Excess molar volumes and viscosities for binary mixtures of butyrolactone with methyl formate, ethyl formate, methyl acetate, ethyl acetate and acetonitrile at 298.15 K were reported by Lu et al. [10]. The survey of literature shows that there are no reports on molec- ular interaction studies of the system undertaken in the present study. The present work is an attempt to elucidate the molecular interactions between methyl formate and ethanol at 303, 308, and 313 K by ultrasonic tech- nique. 1 The article is published in the original. EXPERIMENTAL Binary mixtures were prepared by mixing appropri- ate volume of the liquid components in the standard flasks with air tight caps. The masses were recorded on digital electronic balance (ACM-78094L, ACMAS Ltd., India) to an uncertainty of ±1 mg. The density and viscosity were measured by using specific gravity bottle and Ostwald’s viscometer with accuracy of ±0.01 kg m –3 and ±0.001 N s m –2 respectively. The ultrasonic veloc- ities in the liquid mixtures were measured with a single crystal ultrasonic interferometer (Mittal Enterprizes, New Delhi, Model f81) operated at 2 MHz, which was calibrated with water. The accuracy of the ultrasonic velocity measurements was in the order of ±1 m s –1 . All measurements were made using a constant tempera- ture bath [INSREF model IRI-016C, India] by circu- lating water from the thermostat with accuracy ±0.01 K. In the present study the chemicals used are of Analytical Grade (AR) purchased from Sd fine Chem- icals, India. The purity of the chemicals was checked by comparing the density (ρ), viscosity (η), and ultra- sonic velocity (U) with available literature data [11– 13] and listed in Table 1. THEORETICAL ASPECTS The different parameters such as ultrasonic velocity (U), adiabatic compressibility (β), acoustic imped- ance (Z) were found using different formulae reported Intermolecular Interactions in Methyl Formate–Ethanol Mixtures at 303–313 K according to Ultrasonic Data 1 S. Elangovan a,c and S. Mullainathan b,c a Department of Physics, Easwari Engineering College, Chennai 600089, Tamil Nadu, India b Department of Physics, A.V.C College of Engineering, Mayiladuthurai 609305, Tamil Nadu, India c Research and Development Centre, Bharathiar University, Coimbatore 641046, Tamil Nadu, India e-mail: elangovan.physics@rediffmail.com Received March 13, 2013 Abstract—Density (ρ), viscosity (η), and ultrasonic velocity (U) have been measured for a binary mixture composed of methyl formate and ethanol at 303, 308, and 313 K. The adiabatic compressibility (β), acoustic impedance (Z), free length (L f ), free volume (V f ), internal pressure (π i ), viscous relaxation time (τ), and Gibbs free energy (ΔG) were calculated from the experimental data. The excess values of these parameters (β E , Z E , , , , τ E , and ΔG E ) have also been calculated using the determined parameters and inter- preted in terms of molecular interactions. The deviations in the sign and values of these excess parameters from the ideal mixing reveal the nature of intermolecular interactions between components of the mixture. Keywords: methyl formate, ethanol, ultrasonic velocity and hydrogen bonding. DOI: 10.1134/S0036024414040086 L f E V f E π i E PHYSICAL CHEMISTRY OF SOLUTIONS