EQUILIBRIUM AND KINETIC STUDIES OF THE REACTIONS OF N-SUBSTITUTED (ETHYLENEDIAMINE-N,N',N'-TRIACETATO)AQUACHROMIUM(III) WITH SEVERAL ANIONS

The reactions [CrY(H2O)](n-3)- + X- ⇌ [CrXY](n-2)- + H2O were investigated at 25.0 °C and I = 1.0 (NaC1O4); Y represents ethylenediamine-N, N, Nʹ, Nʹ-tetraacetate (edta), AKhydroxyethyl)ethylenediamine-N, Nʹ, Nʹ-triacetate (hedtra), ethyl-enediamine-N, Nʹ, Nʹ-triacetate (edtra), and N-methylethylenediamine-N, Nʹ, Nʹ-triacetate (medtra); n is 4 for edta and 3 for hedtra, edtra, and medtra. The equilibrium constants of the reactions were 13.6 ±1.2 M-1 (X- = NCS-), 1.9 ± 0.2 M- (X- = ONO-), and 110 ± 15 M-1 (X- = N3-) for [CrX(hedtra)]-, 12.3 ± 1.0 M-1 for [Cr(NCS)(edtra)]-, 2.1 ± 0.3 M-1 for [Cr(ONO)(medtra)]- 21.8 ± 0.4 M-1 for [Cr(NCS)(Hedta)]-, and 0.57 ± 0.07 M-1 for [Cr(NCS)(edta)]2-. The observed pseudo-first-order rate constants of the reactions (k0) were found to be expressed as k0 = kf[X-] + kb, except for the reactions of [Cr(edta)(H20)]_ with NCS” and of [Cr(medtra)(H2O)] with ONO-. The rate constants of the forward reaction (k;, M-1 s-1) and of the backward reaction (kb, s-1) were kf = 3.32 ± 0.11 and kb = 0.244 ± 0.019 for the reaction with X- = NCS- and Y = hedtra, kf = (2.95 ± 0.10) X 10-2 and kb = (2.40 ± 0.17) X 10-3 for the reaction with X- = NCS- and Y = edtra, kf = 12 ± 2 and kb = 6.24 ± 0.32 for the reaction with X- = ONO- and Y = hedtra, and kf = 19.8 ± 1.2 and kb = 0.189 ± 0.012 for the reaction with X-1 = N3-1 and Y = hedtra, respectively. The k0 values for the reaction of [Cr(edta)(H2O)]-1 with NCS-1 could be expressed as k0 = {KHk1 + k2[H+]}[NCS-]/{KH + [H+]} + {KH Cr(NCS)Y + k-2 [H+]}/{KH Cr(NCS)Y + [H+]} where k1, = 13.7 ± 0.6 M-1 s-1, k-1= 26.8 ± 1.9 s-1, k-2 = 0.773 ± 0.042 M-1 s-1, k-2 = (3.17 ± 0.33) x 10-2 s-1, KH = [H+][[Cr(edta)(H2O)]-]/[Cr(Hedta)(H2O]-] = (1.54 ± 0.16) x 10-2 M, and KH Cr(NCS)Y = [H+][[Cr(NCS)(edta))2-]/[[Cr(NCS)(Hedta)]- Cr(NCS)Y] = (4.08 ± 0.55) x 10-4 M. The k0 values (s-1) for the reaction of [Cr(medtra)(H2O)] with ONO- were found to conform to the equation k0 = {(1.7 ± 0.9) X 10-3 + (0.856 ± 0.065). [HNO2]|[ONO-] + (8 ± 3) X 10-4 + (0.41 ± 0.02)[HNO2]. The mechanisms of the reactions are presented. © 1979, American Chemical Society. All rights reserved.