SOLVENT POLARITY STUDIES OF THE WATER+T-BUTYL ALCOHOL AND WATER+T-BUTYLAMINE BINARY-SYSTEMS WITH THE SOLVATOCHROMIC DYES NILE RED AND PYRIDINIUM-N-PHENOXIDE BETAINE, REFRACTOMETRY AND PERMITTIVITY MEASUREMENTS

The empirical solvent polarity parameters E(NR) and E(T) for the solvatochromic compounds Nile Red (1) and pyridinium-N-phenoxide betaine (2), respectively, have been determined as a function of composition for water+t-butyl alcohol and water+t-butylamine binary mixtures, over the whole composition range at 298 K. For both systems the two parameters vary with composition in a strongly non-linear fashion, and the polarity of the mixture decreases with increasing proportion of the organic cosolvent. The non-linear variation the polarity parameters is attributed to water-cosolvent hydrophobic interactions at low cosolvent contents, and hydrogen-bonding interactions at higher cosolvent contents. Permittivity and refractive index have also been measured at 298 K for both systems, and both properties are strongly non-linear functions of composition.