Solvation and hydrophobic hydration of alkyl-substituted ureas and amides in NN-dimethylformamide + water mixtures

Abstract

Enthalpies of solution of five alkyl-substituted ureas and seven different amides have been determined at 298.15 K in mixtures of NN-dimethylformamide (DMF) and H,O. Methyl substitution of the ureas causes changes in the enthalpies of transfer from H,O to DMF which show that either side of these molecules is solvated independently. From the measurements on the amides it is concluded that methyl substitution at the N atom gives changes in the enthalpies of transfer from H,O to DMF which are different from those caused by methyl substitution at the C atom. Analysis of the data in the mixed solvent shows that introduction of more or longer alkyl groups into the molecules makes both ureas and amides considerably more hydrophobic. After accounting for the influence of the NH protons, in both ureas and amides, the enthalpic effect of hydrophobic hydration of the solutes was calculated by application of a clathrate-like hydration model. Enthalpic effect of N-substituted methyl groups in ureas and amides prove to be virtually equal. The variation in the enthalpic effects of hydrophobic hydration with the number of C atoms in the n-alkyl group is comparable to that found for alcohols and amines.

Calculation of Five Thermodynamic Molecular Descriptors by Means of a General Computer Algorithm Based on the Group-Additivity Method: Standard Enthalpies of Vaporization, Sublimation and Solvation, and Entropy of Fusion of ordinary Organic Molecules and Total Phase-Change Entropy of Liquid Crystals

“…Mintz et al's [69] paper on the application of the Abraham model mentioned earlier on gaseous solutes dissolved in water and 1-octanol. Further studies were made on N-methylimidazole [70], urea and its derivatives [71][72][73], thiourea and its derivatives [74], carboxamides and their N-substituted derivatives [75][76][77][78], and uracil and its alkyl-, amino-, nitro-and halosubstituted derivatives [79][80][81][82]. Of the accordingly limited number of 465 compounds having experimental enthalpy-of-solvation values in their datalist, 436 have been entered into the calculation of the atom-group parameters, resulting in 61 valid groups allowing the evaluation of the cross-validated prediction of the solvation enthalpy of 373 compounds with a cv-goodness of fit of 0.9546 and a corresponding standard deviation Q 2 of 4.34 kJ/mol as is shown in aggregated manner in Table 3.…”

Solvation of urea and methyl-substituted ureas by water and DMF

“…enthalpy of solution of the acid and mode: is measured in the pure base Due to the ability of urea to act as a strong protein denaturant considerable theoretical and experimental research has been focused on aqueous urea solutions (1)(2)(3)(4)(5). In particular, Somsen and co-workers (3)(4)(5) have studied the thermodynamic enthalpies of aqueous solutions of urea and methyl-substituted ureas.…”

“…In particular, Somsen and co-workers (3)(4)(5) have studied the thermodynamic enthalpies of aqueous solutions of urea and methyl-substituted ureas. We have made additional calorimetric measurements on these ureas and have applied a previously developed model (6) to provide more detailed information on the first solvation sphere of dilute solutions of urea in DMF and water.…”

Thermodynamic Study of Oxyethylated Glycols and Their Mixtures with Tertiary Carboxamides

“…Void formation in water is more endothermic than in all other known solvents [28]. The effect of hydrophobic hydration of alkyl radicals in amides, as the most important components of their nonspecific interaction with water, was estimated for dimethylacetamide at 319 kJ mol 31 and for DMF, at 316 kJ mol 31 [39]. However, the enthalpies of hydration of these amides are most contributed by specific interactions [40].…”