Electrocatalytic Dehydrochlorination of Pentachlorophenol to Phenol or Cyclohexanol

The electrocatalytic hydrogenolysis of pentachlorophenol (PCP) was carried out under galvanostatic control, in an aqueous 1 M NaOH solution in which PCP is fully soluble, and on particles of palladium or rhodium supported on alumina (Pd(5%)/Al2O3 or Rh(5%)/Al2O3) and entrapped in a reticulated vitreous carbon (RVC) electrode. On Pd/Al2O3 and at 75 °C, the conversion was complete (>99%) after 16 mol of electrons per mol of substrate (16 F mol-1) were consumed, and phenol was the sole product formed in 98% yield (61% current efficiency). On Rh/Al2O3 and 25 °C, 100% conversion was reached after 24 F mol-1, and cyclohexanol was obtained in 98% yield with some 2% of cyclohexanone (62% current efficiency). The ease of electrocatalytic hyrogenolysis was found to increase in the following order: PCP < 2,6-dichlorophenol < 4-chlorophenol.