Xylene, anodic processes

Alkyl alkanoates are reduced only at very negative potentials so that preparative scale experiments at mercury or lead cathodes are not successful. Phenyl alkanoates afford 30-36% yields of the alkan-l-ol under acid conditions [148]. Preparative scale reduction of methyl alkanoates is best achieved at a magnesium cathode in tetrahydrofuran containing tm-butanol as proton donor. The reaction is carried out in an undivided cell with a sacrificial magnesium anode and affords the alkan-l-ol in good yields [151]. In the absence of a proton donor and in the presence of chlorotrimethylsilane, acyloin derivatives 30 arc formed in a process related to the acyloin condensation of esters using sodium in xylene [152], Radical-anions formed initially can be trapped by intramolecular addition to an alkene function in substrates such as 31 to give aiicyclic products [151]. 

In contrast to the electrochemical route to other important conducting polymers such as polypyrrole and polyaniline, which are obtained anodically and oxidize at the electrode to conducting forms that allow current to be passed continuously, PPV is obtained cathodically and the films formed at solid electrodes are insulating and halt the electrochemical process. Thus, the reduction of a,a,a, a -tetrabromo-p-xylene in aprotic solvents at indium-tin oxide (ITO) or Pt cathodes gives thin PPV films suitable only for optical studies [60, 61]. On the other hand, if the reduction is carried out using a stirred mercury pool cathode [62], the process may be operated at a preparative scale, because any film formed at the electrode is continuously broken up. 

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