Promoted Raney Ni catalyzed hydrodefluorination of fluorophenols under mild conditions via controlling solvents and bases

Abstract

Fluorinated organic compounds (FOCs) are difficult to degrade and persistent in the environment due to the strong CF bond strength. In this context, the applicability of Raney Ni to catalytic hydrodefluorination (HDF) of FOCs under mild conditions remains an important challenge. In this study, the effects of solvent systems and bases on Raney Ni catalyzed HDF reaction were investigated and evaluated with 4-FP using as a model fluoroaromatic compound (FAC). It was found that the HDF reactivity of 4-FP over Raney Ni increased with the increase of water proportion and polarity of homogeneous ethanol–water solvents, and Raney Ni exhibited highest activity and stability in catalytic HDF of 4-FP in water with appropriate NaOH amount (1.5NaOH) under mild conditions. The mechanisms of these phenomena were clarified with the aid of catalyst characterization (SEM, EDX, and XRD) combined with ICP-OES. The results suggested that water could efficiently dissolve inorganic salt (NaF) produced in situ, which avoided the decrease in the catalytic activity of Raney Ni in the HDF of 4-FP due to the deposition of NaF on the surface of the catalyst. Moreover, the appropriate NaOH amount (1.5NaOH) in water could efficiently avoid the corrosion effect of HF on Raney Ni and eliminate the framework collapse of the catalyst resulted from the corrosion of Al. In water with 1.5NaOH, Raney Ni exhibited the highest activity and stability in catalytic HDF of 4-FP, with a complete conversion of 4-FP for at least 10 times. Based on these studies, an efficient reaction system was developed for Raney Ni catalyzed HDF of 4-FP, which would provide guidance to apply Raney Ni for catalytic HDF of FACs under mild conditions.