Kinetics of the Cu(II) – Nitrilotriacetic Acid Reaction

Abstract

The kinetics of the reaction between Cu(II) and nitrilotriacetic acid (NTA) to form the 1:1 complex have been studied by the stopped-flow technique over the pH range 2–6. The reaction is kinetically first order in both [Cu(II)] and [NTA]total; the rate constant has a minimum value of 1.1 × 105 l mol−1 s−1 in the pH range 3.5–5 and increases with either increasing or decreasing pH. An explanation for the observed kinetic behavior may be that in the case of the monoprotonated species HNTA2− there is a rate-limiting transfer of a proton from nitrogen before complex formation takes place, and that this transfer is facilitated with increasing acidity.