Deuterium isotope effects in liquid-liquid phase diagrams: Water + phenol and water + 2-methylpropanoic acid systems

Abstract

Phase-separation temperatures T_p have been measured for the systems H₂O+C₆H₅OH_, H₂O+ C₆H₅OD, H₂0+ C_sD₅OD, D₂0+ C₆H₅0H, D₂O+ C₆H₅OD_, D₂O+ C₆D_sOD, H₂O+ (CH₃)₂CHCO₂H and D₂O+ (CH₃)₂CHCO₂H. For water+ 2-methylpropanoic acid, the differences in the T_p-x curves for the exchange and no-exchange systems are striking. For water + phenol, on the other hand, the effect of deuterium-exchange reactions on the T_p-x curves is very small. The results for all systems are in accord with the qualitative predictions of the Rabinovich theory, which accounts for deuterium isotope effects in liquid-liquid phase diagrams in terms of hydrogen bond and London dispersion interactions. Molar excess enthalpies and molar excess volumes at 300.15 K are reported for the system water + 2-methylpropanoic acid. The results are compared with those for water + acetic acid.