Enthalpies of transfer of tetra-alkylammonium halides from water to water–propan-1-ol mixtures at 25 °C

Abstract

The enthalpies of transfer of several tetra-alkylammonium halides in water–propan-1-ol mixtures have been measured. These data are analysed in terms of recently developed solvation theory. The results of this analysis indicate that solvation of the electrolytes involves a net breaking of solvent–solvent bonds at all solvent compositions. The extent of bond-breaking increases dramatically with the size of the tetra-alkylammonium ion in the highly aqueous solvent systems but is relatively insensitive to the size of the cation in solvents with higher alcohol content. The results for the propan-1-ol system are compared to those for t-butanol–water solvent systems.

The change in the extent of solvent–solvent bond-breaking is discussed in terms of changes in the structure of the mixed aqueous solvent system with changing composition. The change in solvent structure appears to occur over a relatively small range of solvent compositions at around 0.25 volume fraction of the alcohol.