Ultrasonic and Thermodynamic Studies on the Aqueous Solutions of Tetramethylurea

Ultrasonic absorption and sound velocity were measured for aqueous solutions of tetramethylurea at temperatures 10–30 °C. Excess compressibility and partial molar volume were obtained. The curves for the concentration dependence of density, viscosity, and absorption show a maximum at about 60 vol% (20 mol%). The excess compressibility curve shows a minimum at the same concentration. It is concluded that a molecular complex of the molar ratio 4: 1 (water: tetramethylurea) linked with hydrogen-bonds is formed at 20mol%. In a dilute solution (below 4mol%), the magnitude of ultrasonic absorption of tetramethylurea solutions is equal to that of 1,3-dimethylurea solutions, but is less than that of 1,3-diethylurea solutions. The tetramethylurea–water interaction is of a similar nature to that between 1,3-dimethylurea and water in a dilute solution.