The kinetics of the reaction between magnesium and EBT

The kinetics of the reaction between Mg 2+ and Eriochrome‐Black‐T (EBT) has been investigated in the pH range between 7.05 and 9.0, in the presence of 12% ethanol. The reaction is found to consist of two parallel paths, one involving the tervalent unprotonated ligand, and one its monoprotonated form. The rate constant for the unprotonated ligand has a “normal” value, whereas that for the protonated form is much lower. The numerical value of the rate constant for the unprotonated ligand obtained from results at a magnesium concentration of 10 −3 M and a pH up to 9.0 is, however, inconsistent with that obtained from results at [Mg 2+ ] = (1 to 4) × 10 −3 M and pH up to 8.1. This can be explained, at least partially, if we assume the intermediate MgHD to lose its proton not only to H 2 O, but also to other bases present in the solution.