Selective Synthesis of Furfurylamine by Reductive Amination of Furfural over Raney Cobalt

Abstract

Effect of metal nature on reductive amination was investigated with biomass‐based furfural as a typical substrate. Among the tested heterogeneous metal catalysts, cobalt proved to be the most effective metal for the synthesis of the corresponding primary amine. Under a relatively mild reaction condition, 98.9 % yield of furfurylamine was obtained over Raney Co and it can be reused more than eight times without a significant decrease in the catalytic performance. By extensively studying the catalytic pathways and reaction mechanism, it is found that the selectivity to primary amine and secondary amine was governed by the relative rate of hydrogenolysis and hydrogenation of the Schiff base intermediate. The superiority of Raney Co in furfurylamine synthesis can be ascribed to its high efficiency on hydrogenolysis of the Schiff base intermediate and its low performance in the hydrogenation of the Schiff base, carbonyl group and furan ring. Furthermore, ammonia greatly promoted the catalytic hydrogenolysis of the Schiff base intermediate over Raney Co without clear deactivation of the metal active sites.

Selective Catalysis for the Reductive Amination of Furfural Towards Furfurylamine by the Graphene-Co-Shelled Cobalt Nanoparticles

“…Analogous to furfural, reductive amination of HMF constitutes a significant fundamental route for the sustainable production of N-containing compounds from renewable biomass. Some of the reported literatures also suggested that the reactivity of HMF in the reductive amination with gaseous or aqueous ammonia was superior to furfural in terms of target yield and reaction conditions 21,22,40 , in according with our results in Entry 39 and 41. Other kinds of biomass-derived platforms such as phenolic model monomers (e.g., phenol and substituted phenol) derived from lignin were also tolerated in our experiments (Entry 46-61).…”

“…This might be caused by the fact that the cobalt-based catalysts were inactive towards the hydrogenation of furfuryl alcohol, in accordance with the higher selectivity towards furfurylamine in Raney Co system when compared to that of Raney Ni (Entry 10,11). Xu et al 21 also confirmed that the cobalt nanoparticles were identified as the active sites for the reductive amination, which is very meaningful to get a satisfied yield of target product. Note: Screening of prepared and commercial catalysts are based on the below conditions: 90 °C, 2 h, 10 mg catalyst, 5 ml ammonia solution (7M NH3 in MeOH), 2 MPa H2, and 0.5 mmol furfural; the better catalyst of Co@C-600-EtOH was selected to further optimize the reaction conditions.…”

“…On another hands, the expensive and scarcity of noble metal-based catalysts arise negative effects on the production cost as well as its large-scale application, which motivates the low-cost and abundant non-noble metal-based catalysts for the reductive amination of furfural 6 . Xu and co-workers 21 indicated that both of the commercial Raney Ni and Raney Co enabled the reductive amination of furfural with ammonia to proceed well, but the latter was proved to be superior to the former in terms of higher selectivity towards furfurylamine as the metallic cobalt facilitates hydrogenolysis of N-furfurylidenefurfurylamine. Additionally, Varma et al 22 prepared a magnetic Fe3O4@SiO2-Ni catalyst with core-shell structure for the reductive amination of furfural in ammonia solution under 115 °C, 2 h and 2 MPa H2, which yield 73 % furfurylamine but meanwhile exhibited extra merits on high stability, facile separability, and long-term reusability.…”

“…The reductive amination of furfural with other N-containing compounds (e.g., aminopropanol, glycine and β-alanine) also proceeded well depending on the type of heterogeneous catalysts, giving rise to 50-90 % yields of the corresponding target amines. Based on the above findings in relation to the reductive amination of furfural, it can be clearly induced that the current state of relevant works commonly has one or several of the following issues 3,4,9,[11][12][13][14][19][20][21] : 1) noble metal-based homogeneous catalysts need complex or even toxic ligands, tedious product/catalyst separation process, difficult catalyst recycles and reusability; 2) heterogeneous catalysts with earth-abundant transition metal can induce reductive amination but commonly requires harsh conditions; 3) structural features of heterogeneous support obviously affect the catalytic activity and selectivity, which requires a more simplified method in catalyst preparation. In attempt to overcome these problems, especially for the development perspectives with sustainable and environmental goals in the near future, several main factors are necessary in providing a relatively brand-new methodology of reductive amination, i.e., green and renewable reacting reagent, a full atom-economic process without any by-product generation, fairly cheap and possible widely applied industrial scalable heterogeneous catalysts, relatively mild condition, easy and convenient procedures of product separation and downstream processing.…”

Earth‐abundant Metal‐catalyzed Reductive Amination: Recent Advances and Prospect for Future Catalysis

“…Raney Co may have a high efficiency on hydrogenolysis of the Schiff base intermediate, low performance in the hydrogenation of the Schiff base, carbonyl group, and furan ring. NH 3 could promote the Schiff base intermediate hydrogenolysis process on Raney Co while the metal active sites were not clear deactivated [43] . As mentioned above, the homogeneous and heterogeneous Co catalyst played an important role in the reductive amination of carbonyl compounds in the past few years.…”