Thermodynamics of protonation of amines. Values of log K, ΔH, and ΔS for the protonation of NN′- and NN-dimethylethylenediamine and NNN′N′-tetramethylethylenediamine

Abstract

The thermodynamic functions ΔG, ΔH, and ΔS for the protonation of NN-dimethylethylenediamine, NN′-dimethylethylenediamine, and NNN′N′-tetramethylethylenediamine at 25 °C in 0·5M-KNO₃ have been determined by potentiometric and calorimetric methods. The values are compared with those published for ethylenediamine and N-methylethylenediamine. The percentage of monoprotonated tautomer for the amines having non-equivalent basic sites were calculated from enthalpy changes and microconstants. For the symmetrical amines (ethylenediamine, NN′-dimethylethylenediamine, and NNN′N′-tetramethylethylenediamine) the ratios between the enthalpy values for successive stages of protonation were found to be constant.