Author(s)

Rabindra N. Roy, Lakshmi N. Roy, John J. Dinga, Mathew R. Medcalf, Katherine E. Hundley, Eric B. Hines, Clark B. Summers, Lucas S. Tebbe, Jamie Veliz

Drury University, Springfield, USA.

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.

Dissociation Constant, ADA, Emf, Buffer, Thermodynamic Quantity

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.