Enthalpies of solution of N,N,N′,N′-tetramethylurea in amides, dimethylsulphoxide, and acetone at 298.15 K

The enthalpies of solution ΔsolHmm were determined for N,N,N′,N′-tetramethylurea in formamide, N-methylformamide, N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulphoxide, and acetone. Measurements were made at 298.15 K and molalities m = (0.004 to 0.031) mol · kg−1 with a precise isoperibol ampoule-type calorimeter. Standard enthalpies of solution ΔsolHm∘ and transfer ΔtrHm∘ from one solvent to another were computed. The enthalpies of solution of the solute in the hydrogen-non-bonding media were found to be endothermic and weak depending on the nature of methylation in a solvent molecule. It was concluded that the solvent proton-donor ability and existing steric hindrances for hydrogen bonding and other intermolecular interactions play the key role in solvation of tetramethylurea.