The electrochemical degradation of i00 ppm aniline and 4-chloroaniline in basic aqueous solutions of pH ranging between I0.i and 12.7 has been studied at constant current intensity using a Pb/PbQ anode and a carbon-polytetrafluoroethylene O2-fed cathode. Under these conditions, hydrogen peroxide was electrogenerated in the cell via a two-electron reduction of oxygen gas fed to the cathode. The current efficiency for H~O2 generation depended on the applied current intensity and the background electrolyte used. The concentration decay for each contaminant with electrolysis time was followed by high pressure liquid chromotography (HPLC). Kinetic analysis of these data showed a pseudo first-order decomposition reaction for both substrates at anodic current densities of 30 mAcm -2 or higher, as well as a decrease of their half-lifetimes when current intensity increased. A gradual decrease in total organic carbon (TOC) for 0.05 tool dm 3 NaOH solutions with electrolysis time was always found. Product analysis of these electrolyzed solutions by gas chromatographymass spectroscopy (GC-MS) and HPLC allowed the detection of nitrobenzene and l-chloro-4-nitrobenzene proceeding from the anodic decomposition of aniline and 4-chloroaniline, respectively. Maleic acid was also detected as intermediate and ammonia was found as final product. Destruction of initial pollutants and intermediates is explained by their oxidative reactions with OH" and HO~ at the anode reaction layer. The effect of HO~ upon decomposition pathways of anilines is discussed.
Electrohydrodimerization (EHD) of 2‐cyclopenten‐1‐one in buffered hydroethanolic solutions containing 50% (v/v) ethanol over the pH range 3.5–12.5 on mercury has been studied by polarography, cyclic voltammetry, and controlled‐potential electrolysis. A one‐electron reduction process is always found, the electroactive species being either its protonated form below pH 6.0 or its unprotonated form above pH 6.3. The diketone (1,1′‐bicyclopentyl)‐3,3′‐dione is obtained as reaction product in all tested media. Voltammetric data allow the proposition that the protonated form is reduced in a one‐electron step to give the corresponding neutral radical, which subsequently couples to yield the final diketone. For the unprotonated form, however, different EHD mechanisms can be established depending on the solution pH. All these pathways are initiated by generation of the radical anion via a one‐electron reduction step. In the pH region 6.3–7.5, the final diketone is formed by dimerization of the neutral radical obtained by protonation of the radical anion with H+ ion. In the pH zone 8.0–11.0, the same hydrodimer is generated via coupling of the radical anion with the neutral radical, followed by protonation of the resulting dimer anion. Under such conditions, voltammetric results indicate that at pH 8.0–8.5, the proton donor is either boric acid of the buffer or H+ ion, whereas at pH 9.0–11.0 it is only the H+ ion. Above pH 11.0 the radical anion couples to form a dimer dianion, which is further protonated by water to give the final diketone. The rate‐determining step of each EHD reaction depends on the voltammetric conditions employed.
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