Kinetics of Substitution of Aquo-ligands from cis-Diaquobisoxalatochromium(III) Ion by Quinolinic Acid in Water―Ethanol Medium

Department of Chemistry, University of Kalyani, Kalyani-741 235

Manuscript received 13 November 1986, revised 24 July 1987, accepted 22 August 1987

The kinetics of substitution of aquo-ligand from 088-diaquobisoxalatochromium(III) ion by quinolinic acid has been studied spectrophotometrically. The following rate law has been established,

                                \(x = {d[Cr(OX)_2(quinH)^{-2} \over dt}=k_2 [Cr(OX)_2(H_3O)_2^-] [quinH^-]\)

in the pH range 2.0— 5.9, where k₂ is the second order rate constant. The rate is slow at low pH around 2, increases with increasing pH and reaches a maximum at pH 4.5, then decreases with further increase of pH. The anation rate and activation para-­meters have been calculated and compared with isotopic water exchange reaction. A reaction mechanism involving SN² path has been suggested.