Solute interactions in dilute aqueous solutions. Part 5.—Microcalorimetric study of polyols and their mixtures with alkanols

Abstract

Heats of dilution of ethanediol, propane-1,2-diol, glycerol and erythritol and their heats of mixing with alkanols with the same number of carbon atoms have been measured at 25 °C; the system propanol + glycerol has also been studied at 5 °C. The various molecular pair and triplet interaction coefficients h_xy, h_xyy etc. have been evaluated. All pair interaction parameters are positive, but the h_yyy coefficients are negative, increasing in magnitude with molecular size. This is an opposite trend to that observed from homologous series of monoalkyl derivatives. The cross-terms h_xy do not lie close to the means of the h_xx and h_yy parameters. The results for the ternary mixtures are compared with similar data for the interactions of polyols with amino acids and proteins. The behaviour of binary polyol solutions is discussed in terms of their possible steric configurations. Schemes for the calculation of thermodynamic properties of polyols, based on the additivity of functional-group contributions, cannot account well for the experimentally established trends.