Gold Catalysis for Selective Hydrogenation of Aldehydes and Valorization of Bio‑Based Chemical Building Blocks

Abstract

Gold catalysts are best known for their selectivity in oxidation reactions, however, there is a promising future for gold in selective hydrogenations. Herein, the hydrogenation of several aldehydes and important bio-based chemical building blocks, namely 5-hydroxymethylfurfural (5-HMF), furfural and vanillin, was performed throughout the combination of Au nanoparticles with Lewis bases. The Au-amine ligand (e.g., 2,4,6-trimethylpyridine) catalytic system could reduce the aldehyde carbonyl group selectively, without reducing alkene moieties or opening the furanic ring that occur on most traditional catalysts. Otherwise, the reduction of nitro group is preferential and the catalytic system was used for the synthesis of furfurylamines, important intermediates in the synthesis of different pharmaceuticals (e.g., furosemide), through the selective reductive amination of furfural starting from nitro-compounds. Moreover, a fully heterogeneous gold catalyst embedded in N-doped carbon (Au@N-doped carbon / TiO 2) was able to perform these reactions in successive recycles without the addition of ligands, with impact in the development of a continuous flow process for biomass valorization.

Sustainable aviation fuel from prehydrolysis liquors

“…Later, this catalyst was tested for the hydrogenation of various aldehydes to alcohols, showing high selectivity. 14 A similar mechanism was also proposed by Nagpure et al, 31 for hydrogenation of cinnamaldehyde, based on the heterolytic dissociation of H2, followed by the transfer of nucleophilic H − ion to electrophilic carbonyl carbon of the aldehyde, whereas the electrophilic H + ion transfers to nucleophilic carbonyl oxygen, leading to the desired alcohol.…”

“…The hydrogenation method follows the conditions reported elsewhere. 14 Furfural (0.1 mmol), Au@NC/TiO 2 catalyst (20 mg, 2 mol%), and 2 mL of 2-propanol were placed in a 4 mL glass vial (with a septum and glass capillary), which was then placed inside a 75 mL stainless steel reactor filled to 2/3 of its volume with quartz sand. The reactor was connected to the H 2 gas supply and placed in the test unit (Series 5000 Multiple Reactor System, Parr Instrument Co., USA) equipped with a Parr 4843 controller for the setup and control of reaction temperature and magnetic stirring speed.…”

“…It is worth to mention that the heterogenous catalyst can be recycled and reused, as demonstrated in the hydrogenation of benzaldehyde. 14…”

Design of gold catalysts for activation of H2 and H-donor molecules: transfer hydrogenation and CO2 hydrogenation

“…Therefore, a fully heterogeneous catalyst composed of gold embedded in N-doped carbon (Au@N-doped carbon/TiO 2 ) that mimics the ligand on the gold surface was developed for the hydrogenation of alkynes 51 and aldehydes. 62 In this case, the ligand cannot be washed out of the surface and the catalysts can be easily reused. The gold–N-doped carbon interface can be also understood as a surface FLP, with an active participation of the support basic nitrogen atoms in the heterolytic H 2 activation.…”

Reduction of Aldehydes with Formic acid in Ethanol using Immobilized Iridium Nanoparticles on a Triazine‐phosphanimine Polymeric Organic Support

“…isopropanol, 82 C, N 2 , 6 hr 93 465 [43] 6 (1.0) HCOONa/HCO 2 H, H 2 O, pH = 2.5, 80 C, 12 hr 96 96 [44] 7 (0.5) glucose, H 2 O, Na 2 CO 3 , 100 C, 20 h 86 172 [45] 8 Au-SiO 2 (1.0) 2,4,6-trimethylpyridine, iPrOH, H 2 (6 bar), 100 C, 24 hr 100 100 [46] 9 Ni-nanoparticles (10.0) HCOONH 4 , THF, 25 C, N 2 , 1.5 hr 85 8.5 [47] 10 Pd-nanoparticles (1.0) H 2 , H 2 O, rt, 6 hr 90 90 [48] stirred for 12 hr at 80 C. Then the reaction mixture was filtered and the filtrate was concentrated under vacuum to yield the crude product. The crude product was purified by column chromatography, eluting with hexane/EtOAc, to afford the desired product.…”