Determination of Infinite Dilution Partial Molar Excess Enthalpies and Volumes for Some Ionic Liquid Precursors in Water and Methanol Using Tandem Flow Mixing Calorimetry and Vibrating-Tube Densimetry

Abstract

A flow mixing microcalorimetric system we developed recently was appended in this work with a vibrating tube densimeter into a tandem flow arrangement. This new combined apparatus (calo/densimeter) allows simultaneous automatic measurement of mixing enthalpies and densities of highly dilute solutions as a function of composition and, in turn, reliable determination of the solute's infinite dilution partial molar excess enthalpies H̅1E,∞ and volumes V̅1E,∞. The performance of the calo/densimeter was verified using 1-propanol in water, and then the apparatus was employed to determine H̅1E,∞ and V̅1E,∞ of several ionic liquid precursors (N-methylimidazole, N-methylpiperidine, N-methylmorpholine, 2-picoline, 3-picoline, and 2,6-lutidine) in water and methanol at 298.15 K. The changes of enthalpy associated with solvation and the transfer of the solutes from water to methanol were evaluated. The thermodynamic behavior observed for individual solutes was compared and briefly discussed in terms of molecular interactions.