Highly Selective Hydrogenative Conversion of Nitriles into Tertiary, Secondary, and Primary Amines under Flow Reaction Conditions

• Published in: ChemSusChem 2022-01, Vol.15 (2), p.e202102138-n/a
• Main Authors: Yamada, Tsuyoshi, Park, Kwihwan, Furugen, Chikara, Jiang, Jing, Shimizu, Eisho, Ito, Naoya, Sajiki, Hironao
• Format: Article
• Language: English
• Subjects: Acetic acid; Amines; Cartridges; Catalysis; Catalysts; Chemical synthesis; Cyclohexane; flow reactions; heterogeneous catalysis; Hydrogenation; Imines; Nitriles; Palladium; Parameters; Solvents
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.202102138

Flow reaction methods have been developed to selectively synthesize tertiary, secondary, and primary amines depending on heterogeneous platinum‐group metal species under catalytic hydrogenation conditions using nitriles as starting materials. A 10 % Pd/C‐packed catalyst cartridge affords symmetrically substituted tertiary amines in good to excellent yields. A 10 % Rh/C‐packed catalyst cartridge enables the divergent synthesis of secondary and primary amines, with either cyclohexane or acetic acid as a solvent, respectively. Reaction parameters, such as the metal catalyst, solvent, and reaction temperature, and continuous‐flow conditions, such as flow direction and second support of the catalyst in a catalyst cartridge, are quite important for controlling the reaction between the hydrogenation of nitriles and nucleophilic attack of in situ‐generated amines to imine intermediates. A wide variety of aliphatic and aromatic nitriles could be highly selectively transformed into the corresponding tertiary, secondary, and primary amines by simply changing the metal species of the catalyst or flow parameters. Furthermore, the selective continuous‐flow methodologies are applied over at least 72 h to afford three different types of amines in 80–99 % yield without decrease in catalytic activities. Three out of one ain't bad: Various tertiary, secondary, and primary amines are synthesized in moderate to quantitative yield by the hydrogenation of nitriles under flow conditions. This method enables selective synthesis of three different types of amine from one type of nitrile by using commercial Pd/C or Rh/C catalysts and solvents. The catalyst‐packed cartridge is continuously used for at least 72 h.