Influence of the acidity level change in aprotic media on the voltammetric behavior of nitrogabacinamamides

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This work presents a comparative voltammetric study of o-, m- and p-nitrogabacinamamides ( N-[3(X-nitrophenyl)-(2E)-propenyl]-4-aminobutanoic acids), NG, in acetonitrile. These compounds, a HDR-NO 2 nitro compounds type, display three reduction waves, two of them are waves similar to those appearing in the reduction of the nitro compounds lacking a proton donor group and one new wave at less negative potentials, associated with the nitro-to-hydroxylamine reduction through a self-protonation reaction. Experiments were carried out in the presence of different chemical species giving an acidity level control by homogeneous buffer systems. The presence of tetraethylammonium phenolate achieves complete inhibition of self-protonation reactions, thus recovering the behavior established by ( − DR- NO 2/ − DR- NO 2 − ) system. When the conjugated acid of the above mentioned base is added to the acetonitrile solution, where the acidity level was controlled by the phenol/phenolate system (acidity level buffer), only the second electroreduction wave ( − DR- NO 2 −/ HDR- NHOH ) shows to be affected by the presence of phenol in the electrolytic medium and displaces towards less negative potential values. On the other hand, in the benzoic acid (HBz)/benzoate (Bz −) medium, the electrochemical behavior of these nitro compounds changes completely passing from ( − DR- NO 2/ − DR- NO 2 − ) system to (HDR-NO 2 + 4HBz/HDR-NHOH + 4Bz −) type system, in which both the stoichiometry of the electroreduction process and the energetic requirement for its realization are changed. The comparison of the different voltammetric behavior in the presence of the different acidic and basic additives allowed constructing an acidity level scale where the different acid base couples of the intermediaries of the NG electroreduction were placed. This kind of scale allows choosing the chemical conditions necessaries to drive the pathway of the electrochemical transformation of nitro compounds.