The 1H-NMR signal of the carboxy methylene protons in Ceedta- or Yedta- is AB multiplet. On formation of the protonated complexes in solutions with lower pH, the multiplet signals are broadened. By means of line-shape analysis, the pH-dependence of the average lifetime (τ) before exchange of the carboxy methylene protons HA and HB was determined (at various temperatures in the case of Ceedta-). The dependence of the rate of the AB exchange process (1/τ) on the H+ ion concentration can be described by a similar relation as for the rate of the proton-catalyzed dissociation of the complexes. On the basis of the rate constants it is assumed that the proton-catalyzed AB exchange process of the carboxy methylene protons in Ceedta- and Yedta- occurs via formation of the same intermediates as in the proton-catalyzed dissociation of Ceedta- and Yedta-. The rate-determining step is also the same in the AB exchange and in the dissociation of the complexes; this is probably the formation of an intermediate containing one free protonated iminodiacetate group.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry