Thermodynamics of dissolution of urea in water, alcohols, and their mixtures

Abstract

A study has been carried out by making use of published data for the solubility of urea to evaluate the thermodynamic quantities associated with the dissolution of urea in water, alcohols, and mixture of these solvents. The ΔG values show an increase with the nature of the solvent in the order water, −1.75; methanol, +2.46; ethanol, +5.74; and 2-propanol, +7.26kJmol−1, respectively. For mixtures containing 33.3, 50, or 66.7% water, there is little difference in the thermodynamic parameters regardless of the identity of the alcohol or the composition of the mixture. In the case of the pure alcohols, values for ΔS and ΔG show that dissolution is most favorable in methanol and least favorable in 2-propanol. For mixtures containing methanol/ethanol, ethanol/2-propanol, and methanol/2-propanol, the solubility data show that the mixture containing ethanol and 2-propanol is the least favorable to dissolution of urea whereas that containing methanol and ethanol is most favorable on the basis of values for ΔS and ΔG. These trends in thermodynamic properties are considered with regard to the nature of the solute-solvent interaction, the expected degree of aggregation of urea in the solvents, and the characteristics of the solvents.