Flow synthesis of secondary amines over Ag/Al₂O₃ catalyst by one-pot reductive amination of aldehydes with nitroarenes

An alumina-supported silver catalyst was investigated in the one-pot reductive amination of aldehydes with nitroarenes in a continuous flow reactor using molecular hydrogen as a reducing agent. A series of secondary amines containing alkyl, OH, OCH₃, Cl, Br and CC groups was synthesized in good to excellent yields. The yield of the secondary amine depends on the rate of formation of an intermediate imine. It was shown that the accumulation of carbonaceous deposits on the catalyst is the main reason of catalyst deactivation. The spent catalyst can be easily regenerated and reused without losing catalytic activity.