Relationship between solvatochromic solvent polarity and various thermodynamic and kinetic data in mixed solvent systems

Abstract

The relationships between solvent polarity in binary mixed solvents, as measured by the solvatochromic E_T values, and various thermodynamic and kinetic data have been investigated with a view to judging the presence of preferential solvation effects. The free energies of transfer, ΔG_t, of simple inorganic ions from water to water–propanol, water–acetone, water–THF mixtures, and the ΔG_t values of whole electrolytes from water to water–methanol, water–propanol, water–acetone and water–THF mixtures do not correlate in a linear fashion with E_T values. On the other hand, ΔG_t data for the solute 1-naphthoic acid transferred from water to water–ethanol mixtures vary linearly with E_T values and it is suggested that this is due to preferential solvation by ethanol. The activities of the organic co-solvent in water–organic solvent mixtures do not correlate linearly with E_T. The rates (as log k) of a range of reactions in mixed solvents correlate linearly with E_T and it is suggested that preferential solvation plays a significant role in influencing the solvent dependence of reaction rate. Anomalous results are observed for the correlation of rate data in the water–methanol system and this is discussed.