Kinetics and mechanism of anation of cis -diaquo- bis -oxalatochromate(III) ion byDL -alanine in ethanol-water mixtures of varying dielectric constant

The kinetics of the anation reaction of cis-diaquo-bis-oxalatochromate(III) ion by DL-alanine has been studied spectrophotometrically in the pH range 3.8 to 7.3, where DL-alanine remains in zwitterionic form. A second-order rate law has been established. Reaction rates in three different ethanol-water mixtures were measured. In each solvent medium the anation rate is higher as compared to water exchange reaction at a particular temperature. The activation parameters (gDH^# and ΔS^#) in different ethanol-water mixtures were obtained from Eyring plots. ΔG^#(ΔH^# −TΔS ^#) values were calculated in each solvent medium and compared with that of the isotopic water exchange process. A reaction mechanism involving theS _N2 path has been suggested.