Kinetics of Ligand Substitution Reactions. 1. A Reinvestigation of the Reaction of Nickel(II) Triethylenetetraminehexaacetate with Cyanide Ion

Article abstract of DOI:10.1021/j100439a004

The kinetics and mechanism of reaction between NiTTHA (where TTHA is triethylenetetraminehexaacetic acid) and cyanide ion at pH 11.0, 25 deg C, μ = 0.1 M (NaClO4) has been reinvestigated.The results are found to be different from those reported by Stara and Kopanica for this reaction, but are in line with results obtained for other aminocarboxylates.The reverse reaction was seen to be suppressed by free cyanide ions which was not accounted for by these workers in their mechanism.A rate expression reflecting this dependence has been proposed.The results obtained in the present work fit a four-step mechanism proposed earlier.The pH dependence of the forward and reverse rates has been investigated and interpreted in terms of the reactivities of CN(1-) and HCN for forward rate and L(n-), HL((n+1)-), and H2L((n+2)-) for reverse rate, respectively.The stability constants of mixed ligand complexes, viz., NiL(CN)(1-n), NiL(CN)2(n-), and also NaL(5-) have been calculated from kinetic data.