Selective Electrosyntheses on Chemically Modified Electrode: IV. Selective Reduction of o-Nitrophenol in the Presence of p-Nitrophenol with α-Cyclodextrin in Solution and on Electrode Surfaces

By controlled potential electrolyses in the presence of α-cyclodextrin (α-CD) in the electrolyte solution, the preferential reduction of o-nitrophenol in a mixture ofo- and p-nitrophenol was achieved. The ratio of the decrease in the concentration of the o-isomer to that of the p-isomer, ω[o-NP]/A[p- NP], was ca. 10 in the presence of a-CD in solution; whereas, the ratio was only 2.2 in the absence of α-CD, indicating that the o-isomer was reduced with good selectivity by the addition of a-CD. These phenomena may be caused by the cathodic shift in the reduction potential of the p-isomer resulting from the selective inclusion of the p-isomer into the cavity of a-CD. a-CD adsorbed or immobilized on graphite electrodes has a similar effect; however, the ratios observed on the electrodes were not high (3.7 and 3.0, respectively).