Energetics of pairwise interaction between glycidol enantiomers in (dimethylformamide + water) mixtures rich in water at T = 298.15 K

Abstract

Successive dilution enthalpies (ΔH(mN-1→mN)) of glycidol enantiomers (R-(+)-glycidol, S-(−)-glycidol) and the racemate (R/S-(±)-glycidol) in (dimethylformamide (DMF)+water) mixtures rich in water (mass fractions of DMF, wDMF=0 to 0.25) have been determined respectively by isothermal titration calorimetry (ITC) at T=298.15 K. The corresponding homotactic enthalpic pairwise interaction coefficients (hXX) of each compound have been evaluated from the framework of McMillan–Mayer theory. Across the studied composition range of (DMF+water) mixtures the hXX values of these compounds are all positive, and decrease gradually with the mass fraction of DMF by the order hRR>hRS≈hMM>hSS>0 (M represents the racemate R/S-(±)-glycidol, and hRS is the estimated value for the heterochiral pair R–S). The positive values of hXX indicate that pairwise interactions of these compounds are endothermic and unfavourable from the point of view of enthalpy. The interaction of S–S pair is considered to be slightly stronger than M–M, R–S and R–R pairs since the former absorbs less heat than the latter in pairwise interactions. The addition of cosolvent (DMF) is in favour of pairwise interactions of these compounds in the mixtures rich in water.