Abstract
Electromotive-force measurements on cells without liquid junction have been used to determine the pK 1 and pK 2 values of glycine in 50 mass % aqueous monoglyme at 11 temperatures from 5 to 55°C. The change in the first dissociation constant is given as a function of the thermodynamic temperatureT by the equation pK 1=−2058.6/T+15.421−0.019169T, whereas that for the second dissociation constant is given by the equation pK 2=1200.5/T+6.7211−0.0042897T. At 25°C, the pK 1 is 2.806 in the mixed solvent, as compared with 2.350 in water; hence, protonated glycine becomes a weaker acid in the mixed solvent. The pK 2 is 9.453 in the mixed solvent, whereas that in water is 9.780, suggesting that the second dissociation process becomes stronger in terms of acidity. The thermodynamic quantities ΔG o, ΔH o, ΔS o, and ΔC op have been calculated, and the results have been discussed with respect to preferential solvation and also compared with similar data for the same two processes in 50 mass % methanol.
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Roy, R.N., Gibbons, J.J. & Snelling, R. Thermodynamics of the dissociations of glycine in 50 mass % aqueous monoglyme from 5 to 55°C. J Solution Chem 6, 475–485 (1977). https://doi.org/10.1007/BF00645841
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DOI: https://doi.org/10.1007/BF00645841