H₂O−D₂O Solvent Isotope Effects on Apparent and Partial Molar Volumes of 1,3-Dimethylurea and Tetramethylurea Solutions

Abstract

Densities of solutions of 1,3-dimethylurea and tetramethylurea in H2O and D2O have been measured at 15, 25, and 40 °C over wide concentration ranges using a vibrating tube densitometer to obtain apparent (VΦ) and partial (V2) molar volumes. A comparison of the data with those for urea shows interesting differences. While for urea is positive, monotonously increases with concentration, and displays an inverse isotope effect, (H) − (D) < 0, values for the methylureas are negative, go through a minimum, and show positive solvent isotope effects which are smaller than those for typical inorganic electrolyte solutions.