Abstract: The acidic dissociation constant of N-(2-acetamido)-iminodiacetic acid monosodium (ADA) has been determined at 12 temperatures from 278.15 to 328.15 K by electromotive-force (emf) measurements of hydrogen-silver chloride cells without liquid junction. At 298.15 K, the value of the dissociation constant (pK2) is 6.8416 ± 0.0004. In response to the need for new physiological pH standards, buffer solutions of NaADA and its disodium salt, Na2ADA would be useful for pH control in the biological region of pH 6.5 to 7.5. The pK2 values over the experimental temperature range are given as a function of the thermodynamic temperature (T) by the equation pK2 = 2943.784/T - 47.05762 + 7.72703 ln T. At 298.15 K, standard thermodynamic quantities for the dissociation process have been derived from the temperature coefficients; ΔH° = 12,252 J·mol-1, ΔS° = -89.9 J·K-1·mol-1 and = -148 J·K-1·mol-1. The results are interpreted and compared with those of structurally related derivatives of GLYCINE.
Cite this paper:
Roy, R. , Roy, L. , Dinga, J. , Medcalf, M. , Hundley, K. , Hines, E. , Summers, C. , Tebbe, L. and Veliz, J. (2014) Dissociation Constant of N-(2-Acetamido)-Iminodiacetic Acid Monosodium (ADA) from (278.15 to 328.15) K. Open Journal of Physical Chemistry, 4, 73-79. doi: 10.4236/ojpc.2014.42011.
 King, E.J. (1951) The Ionization Constants of Glycine and the Effects of Sodium Chloride upon Its Second Ionization. Open Journal of Physical Chemistry, 73, 155-159.
 Roy, R.N., Robinson, R.A. and Bates, R.G. (1973) Thermodynamics of the Two Dissociation Steps of N-Tris(hydroxymethymethylglycine (“Tricine”) in Water from 5?C to 55?C. Journal of the American Chemical Society, 95, 8231-8235.