Abstract
A Taylor dispersion tube has been used to measure mutual diffusion in aqueous solutions of glycine hydrochloride at 25°C and concentrations from 0.0005 to 0.5 M. Analysis of the dispersion profiles shows that the diffusion of glycine hydrochloride (GlyHCl) produces a subtantial additional flow of hydrochloric acid that is liberated by the dissociation: GlyH+ + Cl- ⇌ Gly + H+ + Cl-. Diffusion in this system is, therefore, a ternary process described by the equations J 1(GlyHCl) = − D 11∇C 1 − D 12∇C 2 and J 2(HCl) = −D 21∇C 1 − D 22∇C 2 for the coupled fluxes of total glycine hydrochloride (1) and hydrochloric acid (2) components. The ratio D 21/D 11 of measured diffusion coefficients indicates that up to two moles of HCl are cotransported per mole of GlyHCl. Although protonated glycine diffuses with relatively mobile Cl− counterions, the main diffusion coefficient of glycine hydrochloride, D 11, is lower than or nearly identical to the diffusion coefficient of aqueous glycine. A model for the diffusion of protonated solutes is developed to interpret this result and the large coupled flows of HCl. Diffusion coefficients are also reported for the aqueous hydrochlorides of 3- and 4-aminobenzoic acids.
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Lu, R., Leaist, D.G. Comparison of the Diffusion of Aqueous Glycine Hydrochloride and Aqueous Glycine. Journal of Solution Chemistry 27, 285–297 (1998). https://doi.org/10.1023/A:1022619430507
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DOI: https://doi.org/10.1023/A:1022619430507