Gold and silver catalyzed reductive amination of aromatic carboxylic acids to benzylic amines

Abstract

The reductive amination of benzoic acid and its derivatives would be an effective addition to current synthesis methods for benzylamine. However, with current technology it is very difficult to keep the aromaticity intact when starting from benzoic acid, and salt wastes are often generated in the process. Here, we report a heterogeneous catalytic system for such a reductive amination, requiring solely H2 and NH3 as the reactants. The Ag/TiO2 or Au/TiO2 catalysts can be used multiple times and very little noble metal is required; only 0.025 mol% Au. The catalysts are bifunctional: the support catalyzes the dehydration of both the ammonium carboxylate to the amide and of the amide to the nitrile, while the sites at the metal-support interface promote the hydrogenation of the in situ generated nitrile. Yields of up to 92% benzylamine were obtained.