Ultrasonic Investigations in Ternary Mixtures Containing Water, 2-Butoxyethanol and t-Butanol at 298.15 K

Abstract

Ultrasonic speeds in, and isentropic compressibilities of, aqueous solutions of water + 2-butoxyethanol (2BE)+t-butanol have been determined at 298.15 K. The concentrations of t-butanol at which the ultrasonic speed becomes maximum and isentropic compressibility becomes minimum are found to decrease with increases in the concentration of 2BE, x2BE, in the cosolvent (aqueous 2BE). This behavior indicates that the aqueous ternary solutions are less structured than aqueous t-butanol. In the presence of 2-butoxyethanol, enhancement in the hydrogen bonded structure of water due to hydrophobic hydration between t-butanol and water molecules decreases as the concentration of x2BE in the cosolvent increases. When x2BE>0.2, the ternary solution behaves like a normal liquid. This behavior is also very well reflected in the concentration dependence of the excess ultrasonic speed and excess isentropic compressibility. The optimum concentrations of t-butanol, (\(x_{\mathrm{t}\mbox{-}\mathrm{B}}\))opt, at which extrema in ultrasonic speed, isentropic compressibility, excess ultrasonic speed and excess isentropic compressibility are observed decrease with increase in x2BE in the cosolvent. The results are explained as being due to a reduction in the strength of hydrophobic interactions responsible for enhancement in the structure of water in aqueous t-butanol in the presence 2BE. Beyond (\(x_{\mathrm{t}\mbox{-}\mathrm{B}}\))opt, the hydrogen bonded network of water collapses and water, 2-butoxyethanol and t-butanol molecules interact with each other as normal liquid molecules.