Selectivity Control in Catalytic Reductive Amination of Furfural to Furfurylamine on Supported Catalysts

Abstract

Amines are widely used in the manufacture of pharmaceuticals, agricultural chemicals, polymers, and surfactants. However, amines are mostly produced via petrochemical means, which motivates amine production from renewable resources, such as biomass. However, biomass compounds present added challenges involving poor carbon balances. We show that furfural reacts homogeneously with ammonia to produce reactive primary imines, which form large side products and leads to significant carbon losses. The carbon balance is improved by mixing furfural with furfurylamine prior to reaction to form a secondary imine for use as the reaction substrate. While controlling the primary to secondary amine selectivity is a common challenge in reductive amination, supported metal catalysts, including Ni/SiO2, Co/SiO2, and Ru/SiO2 optimize the primary amine yield to 90 to 94 % by using the secondary imine as the reaction substrate. A qualitative correlation between the primary to secondary amine selectivity with the nitrogen binding energy of metals is identified.

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

“…In addition to furfurylamine, another condensation product of N-furfurylidenefurfurylamine (i.e., 1b) was identified to be one of the intermediates for the reductive amination of furfural. The hydrogenation of N-furfurylidenefurfurylamine could easily produce the by-product of Difurfurylamine (i.e., 1c), while its subsequent thermal cyclization to furfurin (i.e., 1d) has also been noted in previous works 39 . Interestingly, the hydrogenation of furfural into furfuryl alcohol was not detected in our catalyst system, which was commonly observed in other catalytic systems, especially using noble metal catalyst 6 .…”

“…During the process of reductive amination, N-furfurylidenefurfurylamine was identified to be the sole intermediate by gas chromatography, which was formed from the condensation of furfural with furfurylamine via the direct pathway according to the previous literatures 13,39 ; in here, methylfurimidate formed by the condensation of furfural with NH3 was unstable to be detected by gas chromatography. The molar percentage content of Difurfurylamine was mostly eliminated after 4 h while the formation of furfurylamine kept almost unchanged, which suggests that the transformation of N-furfurylidenefurfurylamine into furfurylamine might be the rate determining step 14 .…”

“…The yield of furfurylamine was found to have a positive relationship with reaction temperature, increasing up to 92.4 % with the elevation of temperature from 60 °C to 120 °C; however, the most obvious increase occurred between the range of 60-90 °C where the yield of furfurylamine could reach a relatively high level of 85.8 %. Difurfurylamine were observed at first but nearly not produced at higher temperature, which suggested that the transformation of Nfurfurylidenefurfurylamine into furfurylamine was promoted by the reaction temperature, while the side reaction of the hydrogenation of intermediates into Difurfurylamine was thus inhibited 39 . The formation of furfurin caused by the thermal cyclization always existed but with a negligible value less than 2.8 %.…”

“…This characteristic facilitated the delivery of electron catalyzed by metallic cobalt, thereby forming imines after a dehydration reaction. In the following step, the H-H bond is activated on the surface of Co@C-600-EtOH, and in the meantime, the imine was reduced to furfurylamine by the introduction of H + under a very mild environment eventually 39 . The most accepted reductive amination pathway refers to the nucleophilic addition of amine and carbonyl groups to yield an imine, and the imine was then hydrogenated to the desired amine 25 .…”

Base-Free Synthesis of Furfurylamines from Biomass Furans Using Ru Pincer Complexes

“…Hydrogen gas as reductant is an interesting green tool; however, the method needs to operate under pressure of a highly flammable gas, increasing the operating cost. Nevertheless, there are many examples in the literature using H 2 as reductant for reductive amination with noble and non-noble metal catalysts such as Ru, Au, Ir, Pt, Ni, Co and Fe [5][6][7][8][9][10][11]. Although silane is obtained from waste residues of the silicon industry, their use is still in stoichiometric amounts, generating excessive amounts of waste [12][13][14].…”