Hydrogen Bonding and Proton Transfer Processes during the Electrochemical Reduction of Nitrosobenzene in Acetonitrile

Nitrosobenzene (PhNO) is the central intermediary during the electrochemical reduction of nitrobenzene in the presence of strong and moderately strong proton donors. Its reduction affords phenylhydroxylamine (PhNHOH) as product through a global mechanism involving the exchange of two electrons and two protons. During the analysis from weak to strong proton donors (acetic to trichloroacetic acids), the hydrogen bonding association with nitrosobenzene changes the reduction pathway from stepwise to concerted. The carboxylate ions that are released during the proton transfer steps associate with the phenylhydroxylamine and make its oxidation also concerted. These processes are studied by cyclic voltammetry, and the experimental voltammograms are simulated in the framework of a full mechanism in which the reduction steps as well as those of oxidation are considered. Information about the reliability of the association complexes involved in different steps is obtained from electronic structure calculations.