Thermodynamics of Ionization of Fluoroalcohols in Aqueous Solution: Hexafluoropropan-2-ol and Hexafluoropropan-2,2-diol

Abstract
Calorimetric measurements have led to ΔH0 = 6.37 kcal mol−1 for ionization of aqueous hexafluoro-propan-2-ol (HFIP) and to ΔH0 = 6.00 kcal mol−1 for ionization of aqueous hexafluoropropan-2,2-diol (HFPD). We have combined these values with our ΔG0 values from pK = 9.42 for HFIP and pK = 6.65 for HFPD to obtain ΔS0 = −21.7 cal deg−1 mol−1 for ionization of aqueous HFIP and ΔS0 = −10.3 cal deg−1 mol−1 for ionization of aqueous HFPD. These results (all for 298 °K) show that most of the difference in pK values is due to the large difference in entropy of ionization. The ΔS0 values can be explained largely in terms of solute-solvent interactions.

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