Density, Speed of Sound, and Refractive Index Measurements for the Binary Mixture (1, 4‑Dioxane + Isobutyric Acid) at T = (295.15, 298.15, 301.15, 304.15, 307.15, 310.15, and 313.15) K Taoufik Kouissi,* ,† Adel Toumi, ‡ and Moncef Bouanz †,‡ † Unite ́ de Recherche de Physique des Liquides et d’Optique Non Line ́ aire, De ́ partement de Physique, Faculte ́ des Sciences de Tunis, Campus Universitaire, 2092 El Manar, Tunisia ‡ Laboratoire de Physique des Liquides Critiques, Dé partement de Physique, Faculte ́ des Sciences de Bizerte, Universite ́ de Carthage, 7021 Zarzouna, Tunisia ABSTRACT: Density, speed of sound, and refractive index for the binary mixture (1,4-dioxane (1) + isobutyric acid (2)) were measured over the whole composition range at temperatures T = (295.15, 298.15, 301.15, 304.15, 307.15, 310.15, and 313.15) K and at the atmospheric pressure. From the experimental data, excess molar volume V E , excess isentropic compressibility κ S E , excess speed of sound c E , excess refractive index n E , molar refraction R, and deviation in molar refraction ΔR were calculated. These results have been fitted to the Redlich-Kister polynomial equation. The excess molar volume, excess isentropic compressibility, and deviation in molar refraction were found to be negative, whereas excess speed of sound and excess refractive index were found to be positive for all temperatures. The thermodynamic properties have been discussed in terms of nature of molecular interactions between the components of the mixture. 1. INTRODUCTION 1,4-Dioxane and isobutyric acid have the same molecular formula, C 4 H 8 O 2 . They are important organic solvents that can be used in industrial applications. The determination and prediction of excess thermodynamic properties of liquid mixtures have a great interest for the convenient design of industrial processes like distillation and fluid phase separation. 1 Moreover, they provide useful information on molecular interactions required for optimizing thermodynamic model development as well as their applications in some branches of science. Considerable progress has been made in the theoretical understanding of liquid-liquid mixtures. 2-5 It is important to know the volumetric and ultrasonic properties together with the refractive index. In this work, the densities, the speed of sound, and refractive indices for the binary mixture (1,4-dioxane (1) + isobutyric acid (2)) have been measured over the entire composition range and in the temperatures range (295.15 to 313.15) K at 3 K intervals. In addition, to our knowledge, there are no other published data that are available in the literature. From these experimental data, excess molar volume, isentropic compressi- bility, excess isentropic compressibility, refractive index deviation, excess refractive index, molar refraction, and molar refraction deviation have been calculated over the entire composition range and at each temperature. Excess molar volume, excess isentropic compressibility, excess speed of sound, excess refractive index, and molar refraction deviation data have been correlated using the Redlich-Kister equation. The thermodynamic properties have been discussed in terms of the nature of molecular interactions between the components of the mixture. This work is a continuation of our research group‘s studies on thermodynamic, transport, and critical properties of liquid-liquid mixtures. 6-16 2. EXPERIMENTAL PROCEDURE 2.1. Chemicals. 1,4-Dioxane and isobutyric acid were obtained from Merck with mass purity >99%. All liquids were used without further purification as indicated in Table 1. The experimental values of density, speed of sound, and refractive index of pure liquids at temperature T = 298.15 K were compared with values available in the literature 17-25 and are listed in Table 2, which leads to a satisfactory agreement. 2.2. Apparatus and Procedure. All mixtures of 1,4- dioxane and isobutyric acid have been prepared by mixing known masses of the pure components. The mass is performed by using a digital electronic balance (Sartorius BP 221S) with a resolution of 10 -4 g. The experimental uncertainty in mole fractions did not exceed ±0.0005. Some care was taken into consideration to avoid moisture and dust in the final sample, namely, baking the cells overnight under vacuum and preparing the mixtures in a dust-free area. The cell, in which the isobutyric acid and 1,4-dioxane were mixed together, was immersed in a thermally stabilized water bath with thermal Received: November 23, 2014 Accepted: June 10, 2015 Article pubs.acs.org/jced © XXXX American Chemical Society A DOI: 10.1021/je5010643 J. Chem. Eng. Data XXXX, XXX, XXX-XXX