Effect of Phosphorus Precursor, Reduction Temperature, and Support on the Catalytic Properties of Nickel Phosphide Catalysts in Continuous-Flow Reductive Amination of Ethyl Levulinate

Abstract

Levulinic acid and its esters (e.g., ethyl levulinate, EL) are platform chemicals derived from biomass feedstocks that can be converted to a variety of valuable compounds. Reductive amination of levulinates with primary amines and H2 over heterogeneous catalysts is an attractive method for the synthesis of N-alkyl-5-methyl-2-pyrrolidones, which are an environmentally friendly alternative to the common solvent N-methyl-2-pyrrolidone (NMP). In the present work, the catalytic properties of the different nickel phosphide catalysts supported on SiO2 and Al2O3 were studied in a reductive amination of EL with n-hexylamine to N-hexyl-5-methyl-2-pyrrolidone (HMP) in a flow reactor. The influence of the phosphorus precursor, reduction temperature, reactant ratio, and addition of acidic diluters on the catalyst performance was investigated. The Ni2P/SiO2 catalyst prepared using (NH4)2HPO4 and reduced at 600 °C provides the highest HMP yield, which reaches 98%. Although the presence of acid sites and a sufficient hydrogenating ability are important factors determining the pyrrolidone yield, the selectivity also depends on the specific features of EL adsorption on active catalytic sites.

Highly Efficient and Recyclable Nitrogen-Doped Mesoporous Carbon-Supported Ru Catalyst for the Reductive Amination of Levulinic Acid/Esters to Pyrrolidones

“…In one pathway (path 1), initially, the intermediate imine a was easily generated through the nucleophilic attack of the −NH 2 group to the CO group of LA/esters. Then, imine a was hydrogenated to secondary amine b , followed by the dehydrative cyclization between the −NHR 2 group and the −COOR 1 group to afford the desired pyrrolidones. − The other reaction pathway (path 2) involves the following three steps: (1) formation of an imine a , (2) cyclization of imine a to enamine c , and (3) hydrogenation of enamine c to N -substituted 5-methyl-2-pyrrolidinones. , The hydrogenation step is the rate-determining step in the formation of pyrrolidones, and thus, the hydrogenation catalyst plays a crucial role in this reaction. Several Ir , and Ru complexes have been explored for the reductive amination of LA.…”

“…15−17 The other reaction pathway (path 2) involves the following three steps: pyrrolidinones. 18,19 The hydrogenation step is the ratedetermining step in the formation of pyrrolidones, and thus, the hydrogenation catalyst plays a crucial role in this reaction. Several Ir 20,21 and Ru 22 complexes have been explored for the reductive amination of LA.…”

Transition Metal Phosphide Nanoarchitectonics for Versatile Organic Catalysis

“…Very recently, Bukhtiyarova and co‐workers [ 269 ] investigated the effect of phosphorous, reactant ratio, and reduction temperature on the catalytic hydrogenation reactions. In a flow reactor, the catalytic characteristics of several nickel phosphide catalysts supported on Al 2 O 3 and SiO 2 were investigated for reductive amination of ethyl levulinate (EL) with n‐hexylamine to form N‐hexyl‐5‐methyl‐2‐pyrrolidone (HMP).…”

“…g) Reaction mechanism of the synthesis of primary amines via reductive amination of ethyl levulinate (EL). Reproduced with permission [269]. Copyright 2022, Multidisciplinary Digital Publishing Institute.…”

Reductive Amination of Levulinic Acid to Pyrrolidones: Key Step in Biomass Valorization towards Nitrogen‐Containing Chemicals

“…What's more, it is an excellent advanced polar solvent, [4] which can be used as an outstanding cleaning agent for the production of high‐precision electronics, circuit boards, and lithium batteries [3] . In industrial practices, fossil lactones (i. e., α‐angelica lactone) are usually employed as feedstocks to react with aqueous alkylamine to form pyrrolidones in about 70 % product yield [5] . However, α‐angelica lactone has a certain degree of toxicity and is flammable in nature, and it is rather costly in terms of current market prices [6] .…”