Thermodynamics of the dissociations of glycine in 50 mass % aqueous monoglyme from 5 to 55°C

Electromotive-force measurements on cells without liquid junction have been used to determine the pK₁ and pK₂ 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 pK₁=–2058.6/T+15.421–0.019169T, whereas that for the second dissociation constant is given by the equation pK₂=1200.5/T+6.7211–0.0042897T. At 25°C, the pK₁ 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 pK₂ 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 G^o, H^o, S^o, and C_p^o 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.