The reduction of m-iodo-nitrobenzene: A comparative study using microdisk and channel electrodes

The reduction of m-iodo-nitrobenzene, m-I-φ-NO2, in acetonitrile solution was studied using both microdisk and channel electrodes. A voltammetric wave with a halfwave potential of -1.09 V (vs. saturated calomel reference electrode) was observed and both techniques showed that more than one electron was passed per molecule of the substrate. The rates of mass transport were varied in both electrode systems by changing either the electrode radius in the case of microelectrodes, or the electrolyte flow rate in the case of channel electrodes so as to identify the kinetics and mechanism of the electrode process. Both approaches indicated an ECE mechanism operates: m-I-φ-NO2 + e- → [m-I-φ-NO2]·- [m-I-φ-NO2]·- → I· + ·C6H4NO2 ·C6H4NO2 + HS → φ-NO2 φ.NO2 + e- → [φ-NO2]·- where HS denotes the solvent-supporting electrolyte system. The rate constants for the decomposition of the radical anion, [m-I-φ-NO2]·-, as determined by the two methods, were in excellent agreement and equal to 0.30 (0.05) s-1. Comparisons between the use of microdisks and channel electrodes for such studies are reported and their relative sensitivity assessed