Study of preferential solvation in mixed binary solvents by ultraviolet–visible spectroscopy

Abstract
The longest-wavelength band of N-alkylpyridinium iodide has been studied as a function of the solvent composition in various mixed binary solvents. It has been observed that the quantity [E12–(x1E1+x2E2)] serves as a measure of the extent of preferential solvation, where E and x stand for the position of band maximum and the mole fraction values, respectively, and the subscripts 1, 2 and 12 indicate the pure solvents and their binary mixtures. The local mole fractions of the component solvents have been calculated from the E12vs. bulk mole fraction curves. The nature of the preferential solvation agrees well with the quasi-lattice quasi-chemical theoretical result. Stepwise solvent exchange equilibria, e.g. SAiBj+ B ⇌ SAi–1Bj+1+ A, have been used as a chemical model to explain the experimental findings. The influence of component solvents on the extent of preferential solvation has also been discussed.

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