Electrochemical reduction of nitroso compounds: voltammetric, UV-vis and EPR characterization of ortho- and meta-nitrosotoluene derivatives

Abstract

A comprehensive study of the electrochemical reduction, in different electrolytic media, of two nitroso compounds, i.e. ortho- and meta-nitrosotoluene derivatives has been carried out. Furthermore, UV-vis and EPR spectroscopic characterization of the one-electron reduction product from these derivatives in aprotic media is also reported. Controlled potential electrolysis (CPE) was used to generate the nitroso radical and its detection by cyclic voltammetry, UV-vis and EPR spectroscopy was achieved. In protic media (30% ethanol + 0.1 M Britton-Robinson buffer pH 5-12) both derivatives gave a reversible well-defined peak in the whole pH range on Hg in a reaction involving two electrons to give the hydroxylamine derivative. In mixed aqueous organic media (0.015 M aqueous citrate + DMF: 40:60 and 0.1 M TBAI) at pH > 8 isolation and electrochemical characterization of the nitroso radical anion was achieved. Under these experimental conditions, nitroso derivatives are reduced in a quasi-irreversible mechanism. In aprotic media (0.1 M TBAI in DMF), the nitroso radical anions decay by a dimerization, with rate constant values, k(2),: 4100 +/- 52 (M s)(-1) and 2700 +/- 28 (M s)(-1) for ortho- and meta- nitrosotoluene, respectively. The proposed electroreduction mechanism of the nitroso derivatives were supported by digital simulation through a DIGISIM 2.1 software. version.