Water as a solute in aprotic dipolar solvents: 3. D2O–H2O solute isotope effects on the enthalpy of water dissolution in dimethylsulphoxide, N,N-dimethylformamide and N,N-dimethylacetamide at 298.15 K

The enthalpies of solution of ordinary (H2O) and heavy (D2O) water in dimethylsulphoxide (DMSO), N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) have been measured using an isoperibol sealed calorimeter at 298.15 K. Standard (at infinite dilution) enthalpies of solution and solvation, together with D2O–H2O solute isotope effects on the quantities in question, were calculated. The enthalpies of solution of water H/D isotopologues have been found to be negative by sign and increasing in magnitude on going from DMF to DMSO and DMA. The corresponding positive solute isotope effects are very insignificant and slightly increase in a consequence: DMF < DMSO ≤ DMA. It has been concluded that the enthalpy-isotopic effects of water solvation are qualitatively connected with the donor-accepting and structure-packing properties of the aprotic dipolar solvents compared.

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► Enthalpies of solutions of H2O and D2O in DMSO, DMF and DMA were measured.
► The exothermicity of water dissolution increases in a series DMF < DMSO ≤ DMA.
► D2O–H2O enthalpy-isotopic effects of solution of water are positive in all cases.
► Enthalpy-isotopic effect of solution of water increases in a series DMF < DMSO ≤ DMA.