Potentiometric studies on the formation of metal complexes with trans-1,2- diaminocyclohexane-N,N,N',N'-tetra-acetic acid--I: protonation of the ligand

The protonation of trans-1,2-diaminocyclohexane-N,N, N',N'-tetraacetic acid is studied potentiometrically with the hydrogen electrode. The formation constants have been re-evaluated at 25.0 degrees at an ionic strength of 3.0 (NaClO(4)), with a least-squares treatment of the data. The potentiometric data are explained from the law of mass action, using a model which assumes five different ligands to be present in the solution; the logarithmic stepwise stability constants are then 9.90, 6.72, 3.65 and 3.21 for the mono-, di-, tri- and tetra-protonated ligand respectively.