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Comparative voltammetric behaviour of isatin and some of its Schiff bases at a solid electrode

The electrochemical behaviour of isatin (1) and its Schiff base, 3-arylimino-2H-indol-2-ones (2a-g), has been investigated and compared using cyclic (CV) and differential pulse voltammetry (DPV) techniques at glassy carbon electrode (GCE) in different solvent systems. CV of isatin (1) solution in DMF in 0.1 M LiCl showed two irreversible reduction step due to successive transfer of two electrons leading to formation of dioxindole whereas Schiff bases in this system gave a single two-electron transfer irreversible reduction peak at all scan rates studied. This is due to high basicity of nitrogen atom of imine bond, proton abstraction and second electron transfer are both rapid. The product was secondary amine in case of Schiff bases. However, in acidic BR buffer, isatin (1) is preprotonated and showed a single irreversible one-electron reduction wave due to formation of its dimer, isatide. Controlled potential electrolysis was carried out to find the number of electrons transferred and products were isolated and identified by spectroscopy. Kinetic parameters i.e. charge transfer coefficient (α na ), forward rate constant (K f,h ), diffusion constant (D 0 ½) have also been calculated.