Catalytic hyrodechlorination of chlorophenols in aqueous solution under mild conditions

• Published in: Applied catalysis. A, General Vol. 271; no. 1-2; pp. 137 - 143
• Main Authors: Roy, Heidi M, Wai, Chien M, Yuan, Tao, Kim, Jun-Kyoung, Marshall, William D
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 10.09.2004
• Subjects: Chlorophenols; Formate; Hydrodechlorination (mild conditions); Nickel accelerator; Palladium/alumina; Sodium borohydride; Hydrodechlorination (mild conditions); Nickel accelerator; Formate; Chlorophenols; Sodium borohydride; Palladium/alumina
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/j.apcata.2004.02.053

Hydrogen-saturated water or sodium borohydride were inefficient sources of active hydrogen species for the palladium-alumina accelerated hydrodechlorination (HDC) and subsequent hydrogenolysis of 4-chlorophenol (4-CP) or 2,6-dichlorophenol (2,6-DCP) in water at ambient temperature and pressure. By contrast, hydrogen gas in the presence of Pd0/Al2O3 accelerator mediated both hydrodechlorination and partial hydrogenolysis to cyclohexanone. 4-CP or pentachlorophenol (PCP) was converted quantitatively to cyclohexanone in 1h and subsequently reduced further to cyclohexanol (∼25mol%) after 3h. With ammonium formate, HDC of 4-CP was quantitative but hydrogenolysis to cyclohexanol was sluggish (∼14mol% after 1h). Whereas zero-valent iron or magnesium generated only traces (∼3mol%) of phenol, nickel metal powder (Ni0) and Raney-type nickel (Ni–Al) but not NiCl2 mediated HDC/hydrogenolysis in the presence of NaBH4 but not H2. In these cases, hydrogenolysis, at somewhat elevated temperatures, generated cyclohexanol (14–35mol%) and no cyclohexanone was observed. At elevated H2 pressure (414kPa) and 333K over Pd0/γ-Al2O3, hydrogenolysis of PCP to cyclohexanone was complete after 30min. Further increase in pressure (to 4137kPa) with N2 seemed to accelerate the reaction rate for shorter reaction times (10min) but if CO2 served to increase P, the rates but not the course of reaction were retarded appreciably consistent with competitive inhibition of catalytic sites by CO2.