Add time:08/24/2019         Source:sciencedirect.com

N,N′-diethylethylenediamine-N,N′-diacetic acid and N′,N′-diethylethylenediamine-N,N-diacetic acid were prepared via a classical cyanomethylation process and subsequently isolated by displacement cation-exchange chromatography. N,N′-diethylethylenediamine-N,N′-diacetic acid melted with decomposition at 205–208° and N′,N′-diethylethylenediamine-N,N-diacetic acid at 175–177°. Successive pK1 and pK2 values measured at 25° and μ = 0.10 (KNOa) for N,N′-diethylethylenediamine-N,N′-diacetic acid and N′,N′-diethylethylenediamine-N,N-diacetic acid were, respectively, 6.31, 10.42 and 4.71, 11.65. Log KLnCh+ values of 7.1, 6.9, 7.0, 7.0, 6.9, 7.0, 7.1, 7.1, 7.1 and 6.8 were determined by a potentiometric method for Ch = (anion of N,N′-diethylethylenediamine-N,N′-diacetic acid)2- and Ln = Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+, Lu3+ and Y3+, respectively. Because the pK2 value of N′,N′-diethylethylenediamine-N,N-diacetic acid was so high (11.65), the formation constants of its LnCh+ species could not be ascertained below pH 7. The high pK2 value of unsymmetrical N′,N′-diethylethylenediamine-N,N-diacetic acid has been rationalized by classical arguments.

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