METAL-ION CATALYSIS OF HYDROLYSIS OF SOME AMINO ACID ESTER N,N-DIACETIC ACIDS

The N, N-diacetic acids derived from the amino acid esters ethyl glycinate, butyl glycinate, ethyl alaninate, ethyl valinate, ethyl β-alaninate, and ethyl 4-aminobutyrate were prepared and identified by their nmr spectra. These ligands coordinate strongly with a number of metal ions. The rate of hydrolysis of the metal ion complexes in the pH range 5.0-8.0 depends more on the number of carbon atoms in the N-COOC2H5 linkage than on the substituent, R, of the amino acid ester NH2CHRCOOC2H5, with the exception of valine and leucine ethyl esters. The rates of hydrolysis of ethyl glycinate-N,N-diacetic acid (EGDA) complexed with the metal ions Cd(II), Ni(II), Mn(II), Co(II), Fe(II), Zn(II), La(III), Cu(II), Pb(II), Nd(III), Gd(III), Sm(III), Dy(III), Er(III), Yb(III), and Lu(III) were studied and found to increase in the order listed. Temperature-dependence studies of the rates of hydrolysis were made for the metal ions Cu(II), Pb(II), Ni(II), Sm(III), and Lu(III) and were interpreted in terms of a mechanism consistent with the observed rate law, rate = k[M(EGDA)][OH-], in which an hydroxide ion attacks the carbonyl carbon of the ester which has coordinated to the metal ion in a rapid prior equilibrium. © 1968, American Chemical Society. All rights reserved.