Abstract: The dilution enthalpies of D-mannitol and D-sorbitol in aqueous sodium chloride solution have been determined by using flow-mix-isothermal microcalorimetry at 298.15 K. The enthalpic pairwise interaction coefficients(h2) in the range of sodium chloride concentration (0～1.2 mol•kg-1) have been calculated according to the McMillan-Mayer theory. It is found that h2 of coefficients D-mannitol and D-sorbitol are all positive in aqueous sodium chloride solution and become more positive with increase of the concentration of sodium chloride. Further analysis indicates that the increasing rate of the h2 coefficient [dh2/dm(NaCl)] for D-sorbitol is larger than that of D-mannitol. The results are discussed in terms of the different conformations of the two polylols, interactions of solute with solute and solute with solvent.

Key words: D-mannitol, D-sorbitol, Sodium chloride, Dilution enthalpy, Enthalpic pairwise interaction coefficients