The reductive amination of carboxylic acids is a very green, efficient and sustainable method for the production of (bio-based) amines. However, with current technology, this reaction requires two to three...

Amino acids are considered to be a valuable renewable resource for the production of bio-based chemicals.Here, the Ru-catalyzed hydrogenation−decarbonylation toward primary amines is presented. In contrast to the direct Pdcatalyzed decarboxylation, this catalytic system operates at much lower temperatures, safeguarding the stability of the primary amines. Moreover, instead of producing CO 2 , the cleaved carbon is released as CH 4 , which can be recycled for other applications (e.g., energy purposes). After a general catalyst screening, the Ru-based system is optimized for the model reaction of L-valine in water, resulting in isobutylamine yields of up to 87%. Stronger acidity in the aqueous solution improves the stability of isobutylamine, but simultaneously promotes the parallel formation of 2-amino-3-methylbutane, which is the most important side product. This tradeoff is controlled by adding an appropriate amount of H 3 PO 4 . Besides pH, the other reaction parameters are also screened: H 2 pressure, temperature, and catalyst-to-substrate ratio. Kinetic profiles are recorded to gain a thorough understanding of the reaction network and the product stability. Finally, the stability and broad applicability of the Ru/C catalyst are demonstrated.

Hydrogenation of primary aliphatic amides was achieved in CPME with a novel RuWOx/MgAl2O4 catalyst with yields up to 83%.

Long-chain polyamides (LCPAs) are depolymerized by ammonolysis of the secondary amide bonds into building blocks for new polymer synthesis. Research on the ammonolysis of PA is quite limited and often proposes harsh reaction conditions with homogeneous catalysts. Here, we describe a heterogeneous catalytic system based on Nb 2 O 5 . Reactions were performed at a relatively low temperature of 200 °C in cyclopentyl methyl ether (CPME) as a green solvent and with limited addition of NH 3 and H 2 . The ammonolysis of secondary amides was extensively studied, initially with N-hexylhexanamide as a model compound. Since ammonolysis is an equilibrium reaction, it was eventually coupled to a hydrogenation process, with addition of a RuWO x /MgAl 2 O 4 hydrogenation catalyst, in order to achieve complete depolymerization. Industrial LCPA samples were successfully and completely depolymerized to α,ω-diamine monomers and oligomers, resulting in product distributions of 62% primary amines and 36% secondary amines. The catalytic system was proven to be very robust against a variety of contaminants, e.g., fillers, other plastics, and additives. Only sulfur-containing compounds poison the Ru-catalyst and have to be removed completely.

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.