Enthalpic pairwise self-interactions of urea and its four derivatives in (dimethylformamide + water) mixtures rich in water at T = 298.15 K. (February 2016)

• Record Type: Journal Article
• Authors: Zhu, Li-Yuan; Hu, Xin-Gen; Wang, Hua-Qin; Chen, Nan
• Is Part Of: Journal of chemical thermodynamics. Volume 93(2016:Feb.)
• Page Start: 200
• Page End: 204
• Publication Date: 2016-02
• Subjects: Urea and its derivatives -- (Dimethylformamide + water) mixtures -- Dilution enthalpy -- Enthalpic pairwise self-interaction -- Isothermal titration calorimetry; Thermodynamics -- Periodicals; Thermochemistry -- Periodicals; Thermodynamique -- Périodiques; Thermochimie -- Périodiques; Thermochemistry; Thermodynamics; Periodicals; 541.369
• DOI: 10.1016/j.jct.2015.10.010
• Languages: English
• ISSNs: 0021-9614

Abstract

Graphical abstract: Highlights: Dilution enthalpies of urea and its four derivatives were determined. Enthalpic pairwise interaction coefficients ( h 2 ) were calculated. The h 2 values are all negative in pure water. The h 2 values increase with the content of DMF in mixed solvents. Substituent and solvent effects on h 2 coefficient was discussed. Abstract: Dilution enthalpies of urea (U) and its four derivatives {biuret (BU), methylurea (MU), 1, 1-dimethylurea (1, 1-DMU) and 1, 3-dimethylurea (1, 3-DMU)} in (dimethylformamide (DMF) + water) mixtures of various mole fractions ( x DMF = 0 to 0.10) at T = 298.15 K have been determined by isothermal titration calorimetry (ITC). In light of the approach of McMillan–Mayer's theory, enthalpic pairwise self-interaction coefficients ( h 2 ) of each compound at the corresponding composition ( x DMF ) of mixed solvent (DMF + water) have been calculated. It is found that the h 2 coefficients of each compound are all negative in pure water and increase incrementally with the concentration of DMF in the mixed solvent, following the order h 2 (BU) < h 2 (U) < h 2 (MU) < h 2 (1, 1-DMU) < h 2 (1, 3-DMU). It is concluded that (1) the addition of co-solvent DMF to solvent water is unfavourable to the pairwise self-interactions of these solutes from the point of view of enthalpy; (2) the substitution of methyl (Me) on N atom of urea enhances the component of hydrophobic interactions during the pairwise self-interactions of these solutes; (3) BU is a more hydrophilic molecule than U, and 1, 3-DMU is a more hydrophobic molecule than 1, 1-DMU.