Aniline, anodic electrolysis

Both PAn and PPy can be prepared only by anodic electrolysis at the electrode surface because anilines and pyrroles cannot be reduced within the potential limit of solvents such as water or acetonitrile. 

These polymers, particularly poly(pyrrole), are most conveniently prepared from the parent molecule via electrolysis. So far, furan, pyrrole, thiophene, and various methylated derivatives have been polymerized by this procedure (10). The anodic polymerization apparently also works for relatively electron rich aromatic compounds such as aniline and azulene (11). 

Chelate cobalt complex was synthesized electrochemically by reacting 2-N-tosylamino (2 -hydroxybenzylidene)aniline with 2-amino-l-methylbenzimidazole on a cobalt anode (2x2 cm2 plate) at room temperature. A working acetonitrile solution (50 mL) contained azomethine (0.250 g), N-base (0.185 g), and Et4NC104 (0.01 g). Electrolysis was carried out in a special-purpose electrolytic cell at a direct current of 10 mA with a voltage of 20 V for 4 hr. The resulting green powder was filtered off and recrystallized from ethanol giving brown crystals. 

The above process was applied initially [142,144] to destroy 100 ppm aniline and 4-chloroaniline in alkaline solutions of pH between 11 and 13 by anodic oxidation in the presence of H202 electrogenerated at an ODC (54 mM H202 at 600 mA). Both substrates presented pseudo first-order decays with half-lives less than 30 min at 600 mA. After 11 hr of electrolysis at 300 mA, a TOC decay >95% was found (see Table 4). Nitrobenzene and p-chloronitrobenzene were detected, respectively, as intermediates, which degraded via maleic acid. Cl was quantitatively released from 4-chloroaniline, and NH3 was a final product of both substrates. General reaction pathways involving oxidation of organics by OH and H02 were proposed. 

Table 1. Influence of electrolysis conditions on product distribution in the anodic oxidation of aniline and A -alkylanilines. ...

Table 1 Influence of Electrolysis Conditions on Product Distribution for Anodic Oxidation of Aniline and A-Alkylanilines...

In 1862, Letheby [30] discussed the production of a blue substance by the electrolysis of sulfate of aniline, nowadays considered as the first reported electrochemical synthesis of a conjugated polymer, in his case poly(aniline). Since then a great number of different monomers were synthesized that form conducting polymers. The synthesis method of choice for preparing these polymers involves the anodic oxidation of a suitable monomer M into a cation radical... 

From this figure it is clear that the reaction is highly pH dependent. It has been observed that the prolonged electrolysis can lead to the decomposition of the above product to benzoquinone, which can be represented as The final product of the anodic oxidation of aniline can be summarized as in Table 12.6. 

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