Viscosity and Apparent Molal Volumes of Aqueous Triethylenediamine

The relative viscosities eta(r) and apparent molal volumes phi(V) of aqueous triethylenediamine (or 1,4-diazabicyclo[2,2,2]octane) solution have been measured as a function of concentration at 15 and 25 degrees C and at pH 5.8 and 12.1. The solute is in the hydrochloride form at pH 5.8 and in the free base form at pH 12.1. The viscosity data were treated to yield values of B and D coefficients in the extended Jones-Dole equation, eta(r) = 1 + Ac(1/2) + Bc + Dc(2). Based on the obtained sign and magnitude of (B - 0.0025 (V) over bar (2)degrees') and dB/dT, where (V) over bar (2)degrees is the partial molal volume of the solute at infinite dilution and T the temperature, the hydrochloride is found to be a weak water-structure breaker, while the free base interacts with water and enhances the structure markedly. The effect of protonation on the triethylenediamine is to cause a large decrease in the partial molal volume (by about 11.8 ml-mole(-1)) and a considerable disruption of water structure surrounding the organic molecule [indicated by the decrease in the value of (B(i) - 00025 (V) over bar (2i)degrees) by 0.138 at 25 degrees C and by 0.179 at 15 degrees C]. Our results are in agreement with the water-proton chemical shift measurements and the dielectric relaxation studies.