The Electroreduction of Acrylonitrile: A New Insight into the Mechanism

Several complementary electrochemical techniques have been used in order to clear up the mechanism of the electrochemical reduction of acrylonitrile (AN) on nickel. According to Lecayon et al., the electropolymerization of AN occurs in acetonitrile in the presence of tetraethylammonium perchlorate in such a way that polyacrylonitrile (PAN) is "grafted" onto the cathode. This electrochemical reaction has been reinvestigated both in acetonitrile, a nonsolvent of PAN, and in N,N-dimethylformamide (DMF), a good solvent for the polymer. The key role of the reduction potential on the electrografting reaction has been emphasized. The two electrochemical phenomena previously reported by Lecayon et al. have indeed been confirmed, but now it is clear that the "electrografting" of PAN selectively occurs at the less cathodic potential. At this potential, a PAN film is formed by a radical process and firmly secured onto the electrode, even in DMF. If the cathodic potential is further increased, the PAN film is easily removed from the metal and dissolves quickly in DMF. The transfer of one electron from the metal to the monomer occurs when the reduction is carried out at the more cathodic potential. A nonadherent PAN film is then formed onto Ni in acetonitrile, although the AN polymerization occurs in solution when acetonitrile is replaced by DMF. The AN polymerization is then consistent with an anionic process.