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Volumetric, Viscometric, and Refractive Index Behaviour of Glycine in Aqueous Diols at Different Temperatures
Author(s) -
Ali Anwar,
Khan Shahla,
Hyder Soghra
Publication year - 2005
Publication title -
journal of the chinese chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.329
H-Index - 45
eISSN - 2192-6549
pISSN - 0009-4536
DOI - 10.1002/jccs.200500031
Subject(s) - chemistry , aqueous solution , solvent , moiety , viscosity , diol , analytical chemistry (journal) , stereochemistry , chromatography , thermodynamics , organic chemistry , physics
Densities, ρ, viscosities, η, and refractive indices, n D , of glycine (Gly) (0.1 — 0.5 M) in aqueous 1,2‐ethanediol (1,2‐EtD), 1,2‐propanediol (1,2‐PrD), and 1,3‐butanediol (1,3‐BuD) (30% v/v) were measured at 298, 303, 308, and 313 K. Experimental values of ρ and η were used to calculate partial molar volumes, ϕ 0 v , partial molar volumes of transfer of Gly from water to aqueous diol solutions, ϕ 0 v (tr), Falkenhagen and Jones ‐Dole coefficients, A and B, respectively, free energies of activation of viscous flow, Δμ 0 * 1 and Δμ 0 * 2 , per mole of solvent and solute, respectively, enthalpies, ΔH* and entropies, ΔS* of activation of viscous flow. Large positive values of ϕ 0 v , and an increasing value of S v *, for all the three mixtures at each temperature suggest the presence of strong solute‐solvent interaction, and this interaction decreases as the size of alkyl moiety increases from 1,2‐EtD to 1,3‐BuD. Positive ϕ 0 v (tr) values tend to decrease with increasing the number of CH 2 group, thereby indicating that the electrostriction effect in diols follows the sequence; 1,2‐EtD > 1,2‐PrD > 1,3‐BuD. Small A values, with large values of B, are indicative of weak solute‐solute and strong solute‐solvent interactions that operate in the present systems, and that the magnitudes of B are in the sequence: 1,2‐EtD > 1,2‐PrD > 1,3‐BuD and, thus, the sequence represents the strength of interaction between Gly and diol molecules. Moreover, positive SB/ST values suggest the structure‐breaking nature of Gly in diol + water mixtures. The observed values of Δμ 0 * 2 fall in the sequence: 1,2‐EtD > 1,2‐PrD > 1,3‐BuD which, like ϕ 0 v and S v *, reinforce that Gly‐diol interaction decreases with subsequent addition of CH 2 group in diols. The trends in the variation of ΔH* and ΔS* with Gly concentration also reveal the presence of significant solute‐solvent interaction in all three systems. An almost linear increase in RD with an increasing amount of Gly reveals that Gly tends to increase the polarizability of the aqueous‐diol molecules under study. The variation of all these parameters with concentration of Gly and with temperature suggests the presence of strong solute‐solvent interaction, which decreases as the size of alkyl moiety in diols increases from 1,2‐EtD to 1,3‐BuD.