Thermodynamic properties of 1-butyl-3-methylpyridinium tetrafluoroborate and its mixtures with water and alkanols

In this article, we study the behavior of an ionic liquid (IL) derived from pyridinium, 1-butyl-3-methylpyridinium tetrafluoroborate [b3mpy][BF4], in mixtures with water and with the first alkanols of the series from methanol to butan-1-ol, at the temperatures of (298.15 and 318.15) K. First, the miscibility regions with the alkanols were established at these two temperatures, determining experimentally the liquid-liquid equilibria and the upper critical solution temperature (UCST) for each binary mixture, confirming the quasiexponential variation of the UCST with the alkanol chain. The enthalpies H-m(E) were determined experimentally with a newly designed calorimetric cell, and the excess molar volumes V-m(E) were determined from densities, at (298.15 and 318.15) K. In all cases, the H-m(E) are positive with (dH(m)(E)/dT)p > 0, whereas the V-m(E) are negative for mixtures with alkanols but positive for the mixture of IL + water. The thermal coefficient (dV(m)(E)/dT)p > 0 was also positive in all cases. All data were correlated with a suitable polynomial equation, and the area and volume parameters of [b3mpy][BF4] were calculated. Finally, we give an interpretation of the results and of the behavior of the mixtures.