Transport Properties of Aqueous Solutions of (1R,2S)-(-)- and (1S,2R)-(+)-Ephedrine Hydrochloride at Different Temperatures

Electrical conductivity and mutual diffusion coefficients of aqueous Solutions of two ephedrine enantiomers ((1S,2R)-(+)-ephedrine hydrochloride and (1R,2S)-(-)-ephedrine hydrochloride), at a concentration range of (0 to 0.17) mol.dm(-3) and (0.001 to 0.01) mol.dm(-3), respectively) have been measured. The effect of temperature, ranging from (298.15 to 323.15) K, has also been studied. The experimental data of electrical conductivity follow the Kohlrausch equation, and the hydration radius of ephedrines can be calculated from Walden rule equation. The activation enthalpies of the transport process for ephedrine cations, (1R,2S)-(-)-ephedrine and (1S,2R)-(+)-ephedrine, 7.4 (+/- 0.5) kJ.mol(-1) and 19.3 (+/- 0.4) kJ.mol(-1), respectively, show a slight discrimination between both enantiomers. The experimental data are discussed on the basis of the Onsager-Fuoss model. The Nernst diffusion coefficients for (1 R,2S)-(-)- and ()S,2R)-(+)-ephedrine hydrochloride in water, at (298.15 and 310.15) K, derived froth conductance and from diffusion experiments are in good agreement.