Kinetics and Mechanisms of Reactions of some complexes of Chromium(III). Formation of Oxalatobis(biguanide) chromium(III) Ion from Diaquobis(biguanide) chromium(III) Ion and its Dissociation in Acid Medium

The kinetics of formation of oxalatobis(biguanide)chromium(III) ion from diaquobis(biguanide)chromium(III) ion and oxalate has been studied in aqueous solution (pH ca. 3–4). The results indicate ion-pair formation between the reacting species followed by reaction by an essentially dissociative mechanism (S_N1IP). The kinetics of dissociation of the oxalatobis(biguanide)chromium(III) ion in acid medium has also been studied. The reactions involved are the loss of the two biguanide ligands in stages and by proper choice of acid concentrations and temperature the rates of the two steps could be followed separately. The results indicate S_N2CA mechanism.