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

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.

[1]  Y. Marcus.  Preferential solvation of ions in mixed solvents. Part 2.—The solvent composition near the ion , 1988 .

[2]  Richard A. Williams,et al.  A study in preferential solvation using a solvatochromic pyridinium betaine and its relationship with reaction rates in mixed solvents , 1988 .

[3]  K. E. Newman,et al.  Application of Kirkwood–Buff theory to free energies of transfer of electrolytes from one solvent to another , 1988 .

[4]  M. Pal,et al.  The charge-transfer band of N-alkylpyridinium iodides in mixed aqueous solvents , 1988 .

[5]  P. Suppan.  Local polarity of solvent mixtures in the field of electronically excited molecules and exciplexes , 1987 .

[6]  S. Arai,et al.  WATER IN ORGANIC SOLVENTS AS STUDIED BY SOLVATOCHROMISM , 1986 .

[7]  Michael H. Abraham,et al.  Linear solvation energy relationships. 23. A comprehensive collection of the solvatochromic parameters, .pi.*, .alpha., and .beta., and some methods for simplifying the generalized solvatochromic equation , 1983 .

[8]  Y. Marcus.  A quasi-lattice quasi-chemical theory of preferential solvation of ions in mixed solvents , 1983 .

[9]  K. E. Newman,et al.  Approaches to the problems of solvation in pure solvents and preferential solvation in mixed solvents , 1979 .

[10]  S. Bagchi,et al.  Effect of temperature on the charge transfer band of methiodide of some nitrogen heteroaromatics , 1976 .

[11]  J. Scudder,et al.  Effect of pressure on charge-transfer complexes in solution. II. Complexes formed between ions and between ions and neutral molecules , 1972 .

[12]  E. J. Poziomek,et al.  Properties of ion pairs in solution. The reaction of pyridinium iodide charge-transfer complexes with methyl p-toluenesulfonate , 1970 .

[13]  E. Kosower.  The Effect of Solvent on Spectra. I. A New Empirical Measure of Solvent Polarity: Z-Values , 1958 .

[14]  J. Kirkwood,et al.  The Statistical Mechanical Theory of Solutions. I , 1951 .