Ru-Catalyzed Hydrogenation-Decarbonylation of Amino Acids to Bio-based Primary Amines

Amino acids are considered to be a valuable renewable resource for the production of bio-based chemicals. Here, the Ru-catalyzed hydrogenationdecarbonylation toward primary amines is presented. In contrast to the direct Pd-catalyzed decarboxylation, this catalytic system operates at much lower temperatures, safeguarding the stability of the primary amines. Moreover, instead of producing CO2, the cleaved carbon is released as CH4, 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 H3PO4. 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.