Influence of ΔpK_a and of the molar volume of the base on the viscosity and on the concentration of conducting ions in binary mixtures of phenols and aliphatic amines

Abstract

In this work we measured at 298.2 K the viscosities ' 1, the conductivities K and the densities of the binary mixtures of 4NOZ-phenol with triethylamine (TEA) and of phenols with lower acidities with dibutylamine (DBA) or trihutylamine (TBA) . The metastable liquid TEA-4W2-phenol mixtures exhibit a maxim1 viscosity as high as 8270 cpoise at a mole fraction xA = 0.71 of the acid. ions, as can be deduced from the product ~' 1 using Walden's rule as a first approximation. For the systems with the weaker phenols, for which ApKa is lower than 2.5, a mrked part of the amine is present under the shape of non-conducting entities and the viscosity maxima are m c h lower. Passing from the ethyl bases to the butyl bases does not trigger important changes in the height or in the position of the visocosity peaks. smaller, but this effect is cancelled off by the rise of the molar volumes which enhances rhe viscosity. groups of the bascs by butyl groups is partly due to the decrease of the dielectric constant of the solutions. Around this mole fraction the mixtures are mainly constituted by conductingThe ion concentrations become muchThe drastic drop of the ion concentration in the mixtures when replacing the ethyl This results from the diminution of the number of dipoles per unit volume. Not only the concentration of the conducting ions and their volume determine the viscosity of the mixtures but also the volume of the non-conducting entities which are present into the solution. bulky triethylamine can be related to the difference in the shape of both molecules.