Thermodynamic Characteristics of Uranyl Benzenesulfonate and p-Toluenesulfonate

The enthalpies of solution of anhydrous and hydrated uranyl benzenesulfonate (I) and p-toluenesulfonate II) in 4 M HCl were determined. The standard enthalpies of formation of I and II and their crystal hydrates from uranium trioxide, sulfonic acids, and water and enthalpies of water addition to anhydrous salts and lower hydrates of II were calculated. The enthalpy of addition of water molecule to II·H₂O is about half that of addition to II·3H₂O. With regard to all approximations in calculations, the enthalpy of formation of II from amorphous uranium trioxide and aqueous solution of the corresponding acid is by approximately 20 kJ mol^-1 more negative as compared to I. It was concluded that the electron-donor power of the p-toluenesulfonate ion is noticeably greater than that of the benzenesulfonate ion, which determines the difference in the properties of II and I.