Thermodynamic properties of aqueous solutions of pyridine and piperidine

This research was designed to examine the thermodynamic properties of aqueous solutions of pyridine and piperidine. The density, excess molar enthalpy of mixing, HE, and excess molar volume of mixing, v E of piperidine–water and pyridine–water mixtures were studied at three temperatures, ranging from 294 K to 315 K. The HE and v E are negative for both mixtures, minimizing at a water mole fraction of about 0.55. The minimum HE for piperidine–water mixtures is −2.23 kJ/mol which is compared with −1.63 kJ/mol for pyridine–water mixtures. The minimum v E are about −1.7 cm3/mol and −0.7 cm3/mol for piperidine–water and pyridine–water mixtures, respectively. The thermal expansion coefficients αT at 303 K, calculated from the density studies, exhibited significant positive deviations (about 20%) from ideality for piperidine–water mixtures. In contrast to this pyridine–water αT only exhibited small positive deviations from ideality of about 2%. The results predict decreases in the absolute magnitude of v E with an increase in temperature which are 5. × 10−3 cm3/K mol and 1. × 10−3 cm3/K mol, for piperidine–water and pyridine–water mixtures, respectively. The results for v E for piperidine–water mixtures agree with the very precise work of Afzal et al., J. Chem. Thermodyn. 40 (2008) 47–53. The data are interpreted in terms of the greater number of opportunities for hydrogen bonding interactions between the unlike molecules for the piperidine–water mixtures.