Cu-Al mixed oxide derived from layered double hydroxide as an efficient catalyst for continuous-flow reductive amination of aromatic aldehydes

BACKGROUND: Secondary amines are important intermediates in the manufacture of pharmaceuticals and other valuable chemicals. Hence, there is a continuing interest in cost-effective and environmentally friendly methods for producing these compounds. Reductive amination of aldehydes or ketones with primary amines over heterogeneous metal catalysts is an attractive approach due to the use of inexpensive and environmentally benign molecular hydrogen as a reducing agent. RESULTS: Various secondary amines were obtained by two-step reductive amination of benzaldehyde derivatives and furfural with primary amines. The condensation of aromatic aldehydes with amines at room temperature in low water methanol gives imines, which are then hydrogenated in a flow reactor over CuAlOx catalyst derived from layered double hydroxide. This process does not require isolation and purification of intermediate imines and can be utilized to obtain several secondary amines in good to excellent yield. The time-dependent study showed that CuAlOx catalyst demonstrates excellent stability in imine hydrogenation. CONCLUSION: An environmentally friendly procedure has been developed for the synthesis of secondary amines through a reductive amination of aromatic aldehydes with primary amines over Cu-based catalyst. This procedure presents a novel way for the sustainable production of secondary amines. (C) 2020 Society of Chemical Industry