Enthalpies of solution of 1,1,3,3-tetramethylurea in normal and branched alkanols (C2–C4) at 298.15 K

The enthalpies of solution ΔsolHmm were determined for 1,1,3,3-tetramethylurea in ethanol, 1-propanol, 2-propanol, 1-butanol, and t-butanol (2-methyl-2-propanol). Measurements were made at 298.15 K and molalities m ≅ (0.007 to 0.036) mol · kg−1 with a precise isoperibol ampoule-type calorimeter. Standard enthalpies of solution ΔsolHm∘ and transfer ΔtrHm∘ from one alkanol to the other (including methanol) were calculated. The obvious relationship between the enthalpic and volumetric effects of solution of tetramethylurea in the n-alkanols (C1–C4) was discovered. The enthalpic effects of transfer caused by branching of the alkanol molecules, 1-propanol → 2-propanol, and 1-butanol → t-butanol, are opposite in sign and dominated by the configurational changes in the solvation environment of tetramethylurea.