Voltammetric studies of aromatic nitro compounds: pH-dependence on decay of the nitro radical anion in mixed media

In this report we have chosen ethyl-m-nitrobenzoate (EMNB) as a prototype of a nitroaromatic compound in order to carry out a detailed cyclic voltammetric study focused on the coupled chemical reaction of the generated nitro radical anion. The study was carried out in mixed media (water+DMF) at different DMF contents and several pH values on both mercury and carbon electrodes. In order to study the coupled chemical reaction it was necessary to choose a narrow pH range between 8 and 10. The coupled chemical reaction follows second order kinetics and we have used Olmsteadʹs procedure to calculate the second order rate constant k2. The k2 values are strongly pH dependent. Typical values of k2=are 1.68×104 l mol−1 s−1 and 1.15×104 l mol−1 s−1 for 60% DMF, pH 9.5 on mercury and GCE, respectively. Considering an EMNB concentration of 0.1 mM the corresponding half life time values were 0.59 s and 0.86 s.