Electrochemical Debromination of 1-Aryl-1,2-dibromo-2-nitropropanes in Dimethyl Sulfoxide

Electrochemical debromination reactions oferythro-dl-l-aryl-l,2-dibromo-2-nitropropanes la-d at a platinum electrode have been investigated by cyclic voltammetry in 0.10 M LiClO₄/DMSO. The reactions produced (E)-l-ary--2-nitropropenes 2a-d in high yields. The cyclic voltammograms were irreversible and the reduction current decreased as the number of cycles increased. The peak potential for the reductions wavss are in the range of —0.51 to —0.56 V (vs Ag/Ag+) and show no clear trend with different aryl substituent. The current density increased as the concentration of the substrate increased. The slopes of the plots of log(I/A) vs log[C] are close to unity, indicating unimolecular processes. For all reactions, the Tafel slopes are in the range of 115-125 mV. The logarithm of the ratio i_X/in at -0.16 V did not correlate with the Hammett substituent constants. From these results, the mechanism of these reactions is assessed.