Kinetics and Mechanisms of the Reaction of Aluminium(III) with Polyaminocarboxylic Acids

Abstract The kinetics and mechanisms of the reactions of aluminium(III) with ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) have been investigated in aqueous solution at 25°C and ionic strength 0.5 mol dm-3 NaClO4. Al3+ reacts with the H4DTPA- and H3DTPA2- with rate constants of 2.06(±0.35) and 19.3(±1.6) respectively while Al(OH)2+ reacts with H3DTPA2- with a rate constant of 1.34(±0.20) × 103 dm3 mol-1 s-1. The outersphere association constant for reaction of Al3+ with H3DTPA2- was found to be 175(±38) mol-1 dm3. Al3+ reacts with H3EDTA and H2EDTA2- with rate constants of 4.73(±1.25) and 21.5(±2.21) dm3 mol-1 s-1 respectively. The outer-sphere association constant for reaction of Al3+ with H2EDTA2- is 164(±52.9) mol-1 dm3.