Kinetic and mechanistic studies on the complexation of aquachromium(III) with DL-tryptophan in aqueous acidic media

Abstract

Aquachromium(III) has been found to form a 1 : 3 complex with DL-tryptophan. The kinetics of the reaction has been followed over the range pH 2.75–3.75 by visible spectrophotometry. The effect of the total ligand and chromium(III) concentrations, ethanol content, and temperature on the rate of the reaction was determined. The results are best accounted for by the ‘Eigen-Tamm’ mechanism. A rate law based on the outer-sphere complexation equilibrium preceding the anation has been established. Values for the outer-sphere complex-formation constants were also calculated from the kinetic data. Anations of [Cr(H₂O)₆]³⁺ and [Cr(H₂O)₅(OH)]²⁺ are discussed in terms of associative interchange (I_a) and dissociative interchange (I_d) mechanisms.