The mechanism of electrochemical oxidation of p-phenylenediamine and 4-aminophenol in the presence of malononitrile, as a nucleophile is studied in a phosphate buffer solution (0.15 M) mixed with ethanol (v:v) using the cyclic voltammetry, controlled-potential coulometry and UV-spectroscopy methods. The results obtained indicate that the oxidation form of p-phenylenediamine and 4-aminophenol participate in the 1,4-michael addition reactions with malononitrile via the ECECCC mechanism (E: electrochemical and C: chemical) for the electrochemical synthesis of new indole derivatives with good yield under controlled potential conditions. The products obtained were characterized after purification by the FT-IR, H-1 NMR, C-13 NMR, mass spectroscopy and elemental analysis. (C) 2014 Elsevier B.V. All rights reserved.