Electro-catalytic scission of carbon-iodine bonds. Building of SAMs at gold surfaces through long chain primary radical adsorption

Primary alkyl iodides (RI) are reduced at smooth gold electrodes in polar organic solvents such as N,N-dimethylformamide (DMF) in the presence of divers tetraalkylammonium salts (TAAX). Beside a main two-electron step currently observed at potential > -2.0 V vs Ag/AgCl, a bell-shaped step appears with all organic iodides within a potential range between -0.6V to 1.2V. This peak does not depend on the organic substrate concentration, its current is proportional to the scan rate in voltammetry; it disappears at the second scan. These features arise form slow adsorption of the RI at gold, followed by an electro-catalytic reduction induced by the metal. It is expected that this (simple) process allows the formation of alkyl radicals readily adsorbed at the metal surface and thus produced layer strongly inhibits the main cathodic step at more negative potentials. With linear chains in C10, C12, C16 and C18, the coverage of gold leads to self-assembled monolayers (SAMs). The compactness of this coverage was found to be about 10 mol cm.