Kinetics of reduction of tris(dithiocarbamato)iron(III) complexes by oxalic acid - influence of added dithiocarbamate ligand on the rate of reaction

The reduction of tris(diethyldithiocarbamato)iron(III), (Fe(dedtc)(3)); tri s(dimethyldithiocarbamato)iron(III), (Fe(dmdtc)(3)); tris(N-methyl,N-phenyl dithiocarbamato)iron(III) (Fe(N-me,N-phdtc)(3)) and tris(morpholine- N-carb odithioato)iron(III), (Fe(morphdtc)(3)) by oxalic acid in benzene-methanol mixtures has been found to proceed with a first order dependence on the [co mplexes]. The order with respect to oxalic acid increases with an increase in [oxalic acid]. An induction period has been observed in the presence of added dithiocarbamate ligand and variation in the concentration of the liga nd increases the rate of reduction of [Fe(dmdtc)(3)] and [Fe(dedtc)(3)] and decreases the rate of reduction of [Fe(N-me(chi)N-phdtc)(3)], while it has no effect on the rate of reduction of [Fe(morphdtc)(3)]. Increase in the d ielectric constant of the medium increases the rate of the reaction. The ra tes of reduction of the various complexes employed were in the order, [Fe(d edtc)(3)] < [Fe(dmdtc)(3)] similar to [Fe(morphdtc)(3)] < [Fe(N-me,N-phdtc) (3)]. These results are explained by assuming a dissociation equilibrium be tween tris(dithiocarbamato)iron(III) and a bis(dithiocarbamato)iron(III) sp ecies through the dithiocarbamate ligand. A suitable mechanism has been pro posed.