Nitroradical anion formation from some iodo-substituted nitroimidazoles

The electrochemical behavior of iodo nitroimidazole derivatives such as 1-methyl-4-iodo-5-nitroimidazole (M-I-NIm) and 1-methyl-2,4-diiodo-5-nitroimidazole (M-I-2-NIm) and the parent compound 1-methyl-5-nitroimidazole (M-NIm), was studied in protic, mixed and non-aqueous media. The electrochemical study was carried out using Differential Pulse Polarography (DPP), Cyclic Voltammetry (CV), Differential Pulse Voltammetry (DPV) and coulometry and as working electrodes mercury and glassy carbon were used. As can be expected, in all media, the effect of introduce iodo as substituent in the nitroimidazole ring produced a decrease of the energy requirements of the nitro group reduction. Certainly, this fact can be explained by the electron withdrawing character of the iodo substituent that acts diminishing the electronic density on the nitro group thus facilitating their reduction. In all the studied media the reduction of M-NIm produced a detectable signal for a nitro radical anion derivative. In the case of M-I-NIm the nitro radical anion was only detectable in both mixed and non-aqueous media. On the other hand the nitro radical anion for the M-I-2-NIm was detected only in non-aqueous medium. When glassy carbon electrode was used as the working electrode in a mixed medium a detectable nitro radical anion derivative appeared for all compounds, thus permitting an adequate comparison between them. The obtained values of k(2) for M-NIm, M-I-NIm and M-I-2-NIm in nonaqueous medium were 5.81 X 10(2), 132 x 10(2) and 1100 x 10(2) M-1 s(-1), respectively. From the obtained k(2) and t(1/2) values in this medium, it is concluded that there is a direct dependence between the presence of iodo substitution in the nitroimidazole ring with the stability of the nitro radical anion.