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Publication costs assisted by KUL and FCFO, Belgium Mixing of aliphatic amines with phenols brings about a spectacular increase of the viscosity which in some cases becomes more than a hundred times greater than that of the pure liquid compounds. These mixtures are also characterized by a great volume contraction, the maximum of which occurs in the vicinity of a mole fraction xa = 0.67 in phenol. The maximal viscosity does not correspond with the maximum in the volume contraction but is shifted toward higher values of xa. The electric conductivity as a function of xa shows in some cases two maxima but this is no longer the case for the product , the single maximum of which lies in the vicinity of that of the viscosity, is proportional to (w,)2Ci where (w¡) is the mean Walden product of the ions and SC¡ their total concentration. It appears that the enhancement of the viscosity occurs in the range of mole fractions where , and thus the ion concentration, becomes nonnegligible. The high value of the viscosity of this mixture is thus related to the presence of ions which are also responsible for the conductivity. These ions are not directly derived from the ab complexes although these are characterized by important volume contractions which extend to parts of the molecules outside the hydrogen bond and which depend on the acid strength of the phenol. The addition of a second phenol molecule to the ab complex causes a marked increase in the volume contraction but the 82b complexes are not yet principally responsible for ion formation and for the increase of the viscosity. This is realized by a"b complexes of still higher stoichiometry. The comparison of the and curves shows that cations of several types participate to a significant extent in the conductivity in the region of high viscosity, namely, the homoconjugated ions RgNH+NRg and the cations where R3NH"1" form a hydrogen bond with a lone pair of electrons of the oxygen atom of the phenol. An important role seems to be devoted to the anions where the phenolate ion is bonded with three phenol molecules. The viscosity depends not only on the concentration of the ions which are responsible for the conductivity but also to an important extent on the size of these ions.

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