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Organic electrosynthesis using toluates as simple and versatile radical precursors.

Bibliographic reference Lam, Kevin ; Marko, Istvan. Organic electrosynthesis using toluates as simple and versatile radical precursors.. In: Chemical communications (Cambridge, England), , no. 1, p. 95-7 (2009)
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  17. DigitalSimulations were performed by using DigiElch Pro software
  18. The decomposition of the aromatic radical-anion is faster when the aromatic nucleus bears an inductive electron substituent, such as a methyl group. The methoxy-substituted benzoates are slightly more difficult to reduce but the rate of decomposition of the corresponding anion-radical is similar to that derived from the toluate. Finally, in the case of the simple benzoate, competing addition of the in situ generated radical to the para position of the aromatic ring has been observed
  19. We suspect the tetrabutylammonium cation to be the hydrogen atom donor since only degradation occurred when lithium perchlorate was used as the supporting electrolyte
  20. Standard electrolysis procedure: An H-type cell, with two compartments of 100 ml, separated by a sintered glass with a porosity of 40 μm, was dried during one night at 200 °C. Then, each cell was equipped with a graphite electrode of 6 cm2 and a magnetic stir bar. Both compartments were then flushed with argon during 10 min. After filling them with 5 g of NBu4BF4 and with 100 ml of NMP, freshly distilled under argon, 600 mg (0.6 mmol) of 9-fluorenyl toluate, dissolved in a little NMP, were added to the cathodic compartment and the solution was stirred and heated up to 130 °C. Then, the intensity of the current was fixed at 90 mA and the mixture was electrolysed until completion of the reaction, as shown by TLC or by GC. The cell was then cooled down to room temperature and the catholyte was carefully diluted with 100 ml of 4 N HCl. The resulting solution was extracted 4 times with 30 ml of ether. The organic phases were pooled, dried over sodium sulfate and the solvent was removed under reduced pressure. Finally, the crude product was purified by chromatography on silica gel, using pentane as eluent (Rf = 0.7), affording the title compound as a white powder in 50% yield. This material proved to be identical to an authentic sample of fluorene
  21. A plausible explanation could be a reaction between the fluorenyl radical and the oxide layer of the electrode. Indeed, copper and lead electrodes are usually covered by a reactive oxide layer. In this regard, we have obtained a similar result when using Cgraphite electrodes in non-degassed NMP