Highly efficient enantio-selective hydrogenation of methyl acetoacetate over chirally modified Raney nickel catalytic system

A new method of preparing a tartaric acid modified Raney nickel (TA-MRNi-NaBr) catalytic system has been studied. Raney nickel was modified with (R,R)-tartaric acid. Then, methanol, in which an appropriate amount of NaBr dissolved, was used as the hydrogenation reaction medium. This new catalytic system showed high efficiency and high durability in enantio-selective hydrogenation of methyl acetoacetate (MAA). The influence of the important modifying parameter (modifying pH) and reaction variables (solvent type, the types of inorganic salts and their amount, reaction temperature and hydrogen initial pressure) on the hydrogenation rate and optical yield were systematically investigated. The high optical yield of 85% was achieved at pressure (0.6 MPa) nearly 17-fold lower than those previously used to achieve such results, and the hydrogenation rate was enhanced significantly. For comparison, the conventional TA-NaBr-MRNi catalyst was also prepared. Characterization data confirmed that compared with the conventional TA-NaBr-MRNi catalyst, the improved TA-MRNi-NaBr catalyst had lower weight ratio of Al–Ni, higher total surface area and more acid-corrosion on its surface, which could lead to the high efficiency of the TA-MRNi-NaBr catalytic system.

Graphical abstractUsing methanol containing an appropriate amount of NaBr as the reaction medium, a high optical yield of 85% was achieved in the enantio-selective hydrogenation of methyl acetoacetate over a tartaric acid modified Raney nickel catalyst under comparatively mild conditions (0.6 MPa, 60 °C, 1 h). The characterization data indicated that the improved TA-MRNi-NaBr catalyst had a lower weight ratio of Al–Ni, higher total surface area and more acid-corrosion on its surface. Figure optionsDownload full-size imageDownload as PowerPoint slide