Electrografting of the cyanomethyl radical onto carbon and metal surfaces

Nanometer layers are grafted on the surface of carbon or metallic electrodes by electrochemical reduction of iodo or bromoacetonitrile in acetonitrile. The structure of these layers, (carbon or metal)–[CH2–CH(NH2)–]n, is determined by electrochemistry, ellipsometry and IRRAS. The bond between the surface and the organic layer is evidenced by ToF-SIMS. A mechanism is proposed to account for the formation of the layers: the grafting is assigned to the reaction of the cyanomethyl radical, CH2CN, with the electrode surface and the latter is partly reduced to the cyanomethyl anion −CH2CN that attacks the first grafted –CH2CN group, leading to the growth of the layer. It is also possible to produce the same radical by oxidation of the −CH2CN anion -obtained by deprotonation of acetonitrile-, but in this case only traces of grafting are detected on the electrode as the radical is trapped by the large excess of anions.