Electrochemical reduction of 2,5-dimethoxy nitrobenzenes: nitro radical anion generation and biological activity

Abstract

The electrochemical reduction of four 2,5-dimethoxy nitrobenzene 6-substituted derivatives in aqueous and mixed media by cyclic voltammetry, tast and differential pulse polarography were studied. In aqueous media, pH>8, it was possible to observe a polarographic peak or wave due to the nitro radical anion formation. This fact is not very common in nitro aromatic compounds where the observation of the nitro radical anion formation peak (or wave) requires the presence of inhibitors or aprotic solvent, besides alkaline pH. In mixed media, all the studied compounds show a well-defined reversible couple, due to the one electron reduction of the nitro group to produce the corresponding nitro radical anion. Cyclic voltammetric studies show that the nitro radical anion generated was relatively stable, although this intermediate specie shows a tendency to undergo further chemical reactions. From these experiments, the kinetic behaviour of the nitro radical anions electrochemically generated was characterized and permitted us to calculate the rate constant k 2 of the second order chemical reaction of the radical anions and their half-life. The electrochemical behaviour is correlated with the in vivo studies of oxygen consumption on Trypanosoma cruzi cell suspensions.