Comparison of the Diffusion of Aqueous Glycine Hydrochloride and Aqueous Glycine |
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Authors: | Ruanhui Lu Derek G. Leaist |
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Affiliation: | (1) Department of Chemistry, University of Western Ontario, London, Ontario, Canada, N6A 5B7 |
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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 J1(GlyHCl) = – D11C1 – D12C2 and J2(HCl) = –D21C1 – D22C2 for the coupled fluxes of total glycine hydrochloride (1) and hydrochloric acid (2) components. The ratio D21/D11 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, D11, 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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Keywords: | Aminobenzoic acids diffusion glycine glycine hydrochloride Taylor dispersion |
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