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Abstract:
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In piridine - formic acid buffer and tetramethylammonium chloride solution of pH 4.5 at a dropping mercury or a glassy carbon electrode, nitrofurazone, furazolidone and nitrofurantoin are reduced in a single six-electron wave, the nitro group being reduced to the amine or the hydroxylamine, respectively. Theelectrochemical behaviour of these compounds depends mainly on the nature and position of the substituents. Reduction to the primary amine occurs when the substituents possess available π electrons to conjugate with the nitro group of the aromatic ring, which determines the transformation of the hydroxylamine into the amine via formation of a highly reducible intermediate imine or a quinonoid structure. In contrast, if the formation of the intermediate imine is made impossible by an adverse effect of the substituent, the hydroxylamine does not undergo further reduction. Cyclic voltammograms were recorded at different pH values and at differents can rates in order to identify certain relatively unstable species. The effect of pH on the difussion-limited current and on the E1/2 values of the polarographic waves was also studied and the results obtained were compared with those obtained by cyclic voltammetry. On this basis, and according to the polarographic and cyclic voltammetric data, a reduction mechanism for the nitrofuran derivatives is suggested, in which the importance of the homogeneous chemical reactions associated with the electron-transfer steps is examined. |