Activity and Selectivity Control in Reductive Amination of Butyraldehyde over Noble Metal Catalysts

Abstract

Approaches to control selectivity and activity in the catalytic reductive amination of butyraldehyde with ammonia over carbon supported noble metal catalysts (Ru, Rh, Pd, and Pt) were explored. Detailed analysis of the reaction network shows that the Schiff base N-[butylidene]butan-1-amine is the most prominent initial product and, only after nearly all butyraldehyde had been converted to N-[butylidene]butan-1-amine, amines are detected in the product mixture. From this intermediate, good hydrogenolysis catalysts (Ru, Rh) produce mostly butylamine, while catalysts less active in hydrogenolysis (Pd, Pt) lead to the hydrogenation of N-[butylidene]butan-1-amine to mostly dibutylamine.

Heterogeneous Ru-Based Catalysts for One-Pot Synthesis of Primary Amines from Aldehydes and Ammonia

“…Thus, amination and hydrogenolysis of the Schiff base towards a primary amine was the dominant pathway at high temperature. These results were also in agreement with the literature [33]. The results of our experiments also showed that only very little 2c was formed in the catalysis system when the Ru/γ-Al2O3 was used as the catalyst, which may be due to the weak chemisorption of 2b intermediate on the Ru/γ-Al2O3 surface, resulting in a low rate of hydrogenation to 2c.…”

“…The yield of 2b was about 77% at 40 °C, which declined to 0.1% when the reaction temperature increased from 40 °C to 80 °C. The similar Schiff base intermediate was also found in the previous studies [20,33,38]. A closer look was taken to analyze the products after the reaction at 80 °C.…”

“…The results of our experiments with Ru/γ-Al2O3 conducted at different temperatures (40-80 °C) showed that Schiff base 2b can be easily produced at the low temperature of 40 °C. However, only small amount of the Schiff base was further transformed to 2a by hydrogenolysis at low temperature, which needed a high activation energy [33]. High temperatures would accelerate hydrogenolysis rates and benefit for the production of more primary amine.…”

“…Up to now, most of the heterogeneous catalysts for the amination of carbonyl compounds with NH3 and H2 were reported in patent literatures, such as Ni, Co, and noble metal-based solid catalysts [31]. There were only a few papers about the reductive amination of aliphatic primary aldehydes or ketone with solid catalyst and seldom clarify its process [32][33][34]. For instance, Raney Ni was commonly applied to reductive amination of aldehydes with ammonia in the early literature, but it had several disadvantages including the requirement of high H2 pressure (0.2-12.5 MPa) and low activity and selectivity of the final products [32].…”

“…Bodis and co-workers used carbon supported group VIII noble metal (Pt, Pd, Rh, and Ru) as catalysts for the reductive amination of butyraldehyde with NH3. It was found that Rh and Ru catalysts were active and selective in the production of primary amine under 50 bar H2 pressure, while Pt and Pd catalysts favored for the secondary amine formation [33]. MgO/Al2O3 supported Ru was applied to reductive amination of 2-butyl-2-ethyl-4-cyan-butyraldehyde [34].…”