Salting-in of Alcohols by Symmetrical Tetra-alkylammonium Bromides

Abstract

The changes in free energy, enthalpy and entropy associated with the transfer of several alkanols at high dilution from water to aqueous solutions of some symmetrical tetra-alkylammonium bromides (R4NBr) have been determined at 20°C. The enthalpies were determined calorimetrically for several salt concentrations. The treatment of salt effects based on the scaled particle theory has been applied to the salting-in of butanol by solutions of R4NBr. For this purpose it was necessary to obtain the cation diameter indirectly by fitting experimental salting-in data for alkanes to the theory. It is concluded that the theory is as successful for butanol as it is for the alkanes. The thermodynamic parameters of transfer are consistent with the assumption that the salting-in of alkanols (and alkanes) by R4N+ ions is caused by the formation of short-lived cation-solute “pairs” and the resultant disruption of water structure surrounding both the cation and non-electrolyte.