Hydrothermal Carbonization of Renewable Natural Plants as Superior Metal-Free Catalysts for Aerobic Oxidative Coupling of Amines to Imines

Abstract

Seeking low-cost sustainable catalysts with high stability and excellent catalytic activity to substitute traditional metal or petroleum-based catalysts is a desirable strategy for catalytic reactions. Here, we report a simple fabrication of biomass-derived hydrochar catalysts with various oxygen functional groups by hydrothermal carbonization of renewable natural plants using water at 190 °C. These prepared hydrochars from maple and straw are found to be very effective in the gram-scale aerobic oxidation of a variety of different amines. The results show that most of the imine yields are over 90% (4 h, 100 °C), and the cycling performance of the catalyst can be tested seven times. Mode studies and density functional theory calculations reveal that the surface carboxylic acid groups (adsorption energy = −25.0 kJ/mol for amine) and quinone moieties (adsorption energy = −22.7 kJ/mol for amine or 9.0 kJ/mol for O2) are the dominant active sites of the hydrochar catalyst, which may participate in substrate binding and facilitate amine oxidation. This study provides a simple chemical processing step using natural plants to prepare an ecofriendly and highly active biochar catalyst, allowing the premises of sustainable biomass-derived carbocatalysis to be explored for industrial applications.

A Porphyrin‐Based Covalent Organic Framework for Metal‐Free Photocatalytic Aerobic Oxidative Coupling of Amines

“…Noble metals such as gold, [12] platinum [13] and osmium, [14] have been widely used to catalyze the reaction, which show good catalytic performance. But the high cost limits their potential for large‐scale application [15] . Non‐noble metal catalysts such as copper, cobalt and iron [16] can also catalyze benzylamine heterocyclic amine to synthesize imines with high conversion rate and selectivity, even for the synthesis of asymmetric imines.…”

“…But the high cost limits their potential for large-scale application. [15] Non-noble metal catalysts such as copper, cobalt and iron [16] can also catalyze benzylamine heterocyclic amine to synthesize imines with high conversion rate and selectivity, even for the synthesis of asymmetric imines. However, most of them need to add oxidant, alkali and other auxiliary agents, which make the reaction system complex.…”

Metal Free Porphyrin Photocatalyst Comprising Ionic Liquid with Electron Donor Acceptor Moiety for Visible Light Assisted Oxidative Amination

“…Supporting information consist of the description of synthetic methods, materials and the experimental part which has been used in present work and characterization including FT-IR, 1 H NMR, 13 C NMR, HRMS, GCMS of intermediates, photocatalyst, benzyl-1-phenylmethanimine and 2-substituted benzimidazole. It also includes the structures of comparative study of photocatalyst and leaching test.…”

“…[8] Therefore, heterogeneous catalysts have received precise attention using metal based, [9] polymer based catalysts and organo-catalysts. [10] In this context, [11] different heterogeneous catalyzed systems such as silica gel supported salicylic acid derivatives, [12] biochar catalyst, [13] inorganic ligand supported zinc catalyst, [14] and cobalt complex, [15] alumina-supported gold, [16] activated carbon supported ruthenium nanoparticles, [17] mesoporous manganese-zirconium solid catalyst, [18] and vanadium sites anchored on N-doped porous carbon were reported for the synthesis of imines. [19] Furthermore, many approaches have been implemented for the synthesis of imines using different metal oxides such as cerium oxide, [20] mesoporous copper aluminum mixed metal oxides, [21] and zinc doped aluminum oxide incorporated with gold nanoparticles.…”

Selective Synthesis of Imines by Photo-Oxidative Amine Cross-Condensation Catalyzed by PCN-222(Pd)

“…Imines are a useful nitrogen source for the synthesis of nitrogen-containing heterocycles. − For example, benzimidazoles are cyclic structures that contain an imine moiety, and these heterocycles are important structural subunits in biologically active organic compounds …”