Ultrasonic behaviour of ternary mixtures containing water, dimethylformamide and t-butanol at 298.15 K

Ultrasonic velocities in and adiabatic compressibilities of aqueous solutions of a water+dimethylformamide (DMF)+t-butanol have been determined at 298.15 K. The concentrations of t-butanol at which ultrasonic velocity becomes maximum and adiabatic compressibility becomes minimum are found to decrease with increase in the concentration of DMF in the cosolvent (aqueous DMF). This behaviour indicates that the aqueous ternary solutions are less structured than aqueous t-butanol. This behaviour is also well reflected in the concentration dependence of excess ultrasonic velocity and excess adiabatic compressibility. It is due to a decrease in the ability of t-butanol to form clathrate hydrates owing to the presence of DMF. When the concentration of DMF in the cosolvent (XDMF)>0.2, ultrasonic velocity decreases and adiabatic compressibility increases with the concentration of t-butanol indicating that the ternary solution behaves as a normal solution where in any further addition of DMF or t-butanol leads to destabilization of the hydrogen bonded structure of water and t-butanol looses its ability to form clathrate hydrates in aqueous solutions.