Electro-oxidation and electroreduction of acetonitrile in aqueous acid solution

Potentiodynamic and potential step experiments were performed in 0.05 M H2SO4+0.05 M CH3CN electrolyte at porous platinum electrodes using on-line mass spectroscope (DEMS) for product analysis. During the electro-oxidation of acetonitrile, only processes involving adsorbates have been observed, using transient experiments. Different pathways for these reactions have been identified. Desorption of acetonitrile as the intact compound can be observed at potentials above 0.5 V vs. RHE. Additionally, CO2 is formed above 0.7 V, while NOx is produced above 1.2 V. The electroreduction of bulk and adsorbed acetonitrile at potentials below 0.1 V vs. RHE forms ethane. In order to investigate the number of hydrogen atoms being transferred, measurements were taken in 0.05 M D2SO4+D2O+O.05 M CH3CN. Under these conditions 1,1,1-trideuteroethane is produced below 0.1 V vs. RHE. Experiments with adsorbates were performed at different potentials using a flow-cell technique without acetonitrile in solution. It is shown that the amount of acetonitrile desorbed as the intact molecule during potentiodynamic oxidation of the adsorbate is a function of the potential where the adsorbate is formed. The amount of associatively desorbed acetonitrile is decreased, possibly by reductive removal, if the adsorbate is cycled in the hydrogen region of the platinum electrode prior to the oxidation of the adsorbate. A possible reaction mechanism for the electro-oxidation and electroreduction of acetonitrile is discussed.