Reduction electrochimique de composes organiques en presence de tensio-actifs—IV. Etudes polarographique et spectroscopique des nitroanilines

Abstract

In order to elucidate the location of substrates in micelles we studied the polarographic and spectroscopic (ESR) behaviour of nitroanilines isomers as a function of pH in the presence of a neutral surfactant (BRIJ 35). In basic or neutral media, two polarogaphic waves are observed and the spectra of anion radicals can be recorded during “ in situ” electrochemical reductions. In acidic aqueous solutions and without surfactant, o and p-nitroanilines give a six-electron wave whereas a four-electron wave is observed for m-nitroaniline. If BRIJ is added, the three isomers lead to four electron processes. Presence of surfactant causes a decreasing of the rate of the intermediate chemical step for the ECE mechanism. When the surfactant concentration reaches 0.1 M, electrolysis “ in situ” (pH = 3.5) gives no ESR signal for o- and m-nitroaniline. Under the same conditions, the p-nitroaniline solution exhibits a well resolved spectrum of p-phenyl-enediamine cation radical. Formation of such a cationic intermediate during the reduction process is discussed and its stabilization is conceivable by means of a solvent “cage effect”.