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 / TiO2) 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.
Highlights
Valorization of biomass platform molecules, such as 5-hydroxymethylfurfural (5-HMF) and furfural (FA), has been explored via selective oxidation,[1] esterification,[2] amination[3] and hydrogenation.[4]
Bottari et al.[6] investigated the catalytic hydrogenation of 5-HMF with copper nanocatalysts of various compositions and found that the catalyst mostly led to a mixture of products in which dimethylfuran (DMF) and 2,5-dimethyltetrahydrofuran (DMTHF) were the major products, as well as etherification and ring opening products followed by hydrogenation as by-products
Considering the interest in the selective hydrogenation of bio-based chemical building blocks containing aldehydes that have many selectivity issues, here we explored their conversion on gold-ligand catalyst systems developed in our group for the hydrogenation of alkynes
Summary
Valorization of biomass platform molecules, such as 5-hydroxymethylfurfural (5-HMF) and furfural (FA), has been explored via selective oxidation,[1] esterification,[2] amination[3] and hydrogenation.[4]. Bottari et al.[6] investigated the catalytic hydrogenation of 5-HMF with copper nanocatalysts of various compositions and found that the catalyst mostly led to a mixture of products in which dimethylfuran (DMF) and 2,5-dimethyltetrahydrofuran (DMTHF) were the major products, as well as etherification and ring opening products followed by hydrogenation as by-products Chen et al.[7] reported the use of Pd nanoparticles (NPs) supported on mesoporous graphitic carbon nitride (Pd / mpg-C3N4) for the hydrogenation of 5-HMF leading to the formation of dihydromethyl tetrahydrofuran (DHMTF). The use of Ru NPs (Ru / mpg-C3N4) was reported, which led to the formation of a mixture of DHMTF and hexanediol (HD) (ring opening products) with selectivities of 60 and 40%, respectively
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