Anthracene anodic processes

Fig. 9. Indirect electrosynthetic process for the oxidation of anthracene to anthraquinone [10]. The charcoal column serves to remove organics which lead to corrosion and poisoning of the lead dioxide (Pb02) anode...

Vanadium2 compounds may be employed as catalysts in oxidation, and reduction processes. Por example, anthracene is oxidised to anthraquinone with a lead anode in 20 per cent, sulphuric acid which contains 3 per cent, of vanadic acid. Aniline under similar conditions may be oxidised to benzoquinone, and the latter substance can be efficiently reduced to hydroquinone. Azobenzene and azoxybenzene are stated to give a good yield of benzidine... 

Chou et al. [79] have studied the anodic oxidation of anthracene to anthraquinone in a slurry electrolyte containing both a Mn3+/Mn2" redox mediator and dodecylbenzenesulfonate (DBS) as surfactant. No reaction of anthraquinone is found in the absence of DBS. The main factors affecting the current efficiency of the process were sulfuric acid concentration, current density, particle size of anthracene, temperature, and concentrations of DBS and redox mediator. 

It has been proposed (e.g. Weinberg and Reddy, 1968) that the cation radical is adsorbed on the anode surface, in which state it might react directly with methanol or undergo further oxidation to a dication in a step prior to or concerted with attack by methanol. Methoxylations of anthracenes (Parker et al., 1971) are regarded as ECE processes. 

The indirect electrolytic processes still employ redox reagents but because they are continuously recycled the effluent problem is greatly reduced. The conversion of anthracene to anthraquinone is a typical example of such a process. A concentrated solution of chromium(III) in aqueous sulphuric acid is partially oxidized to dichromate at a Pb (i.e. Pb covered in situ by Pb02) anode... 

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