An interchangeable homogeneous ⇔ heterogeneous catalyst system for furfural upgrading

Abstract

Intercalation of benzimidazolium cations [BI]+ into the nanogalleries of Na+/montmorillonite (MMT) clay leads to generation of recyclable supported precatalysts [BI]+/MMT, which, upon treatment with a base, catalyze furfural self-condensation coupling reaction into furoin in almost constant yields of >96% over the three cycles investigated.

Carbon-Increasing Catalytic Strategies for Upgrading Biomass into Energy-Intensive Fuels and Chemicals

“…5,5′-Dihydroxymethyl furoin (DHMF), 5,5′-bihydroxymethyl furil (BHMF), and 5,5′-bihydroxymethyl hydrofuroin (BHMH) have been developed as HMF-derived monomers for producing polymeric materials (Scheme ), just as 2,5-furandicarboxylic acid and 2,5-bis­(hydroxymethyl)­furan. , Donnelly et al showed that benzaldehyde lyase was active for the self-carboligation of HMF to DHMF (28–42% yield) at room temperature after 18 h, and BHMF (22–45% yield) was also formed via spontaneous oxidation . On the other hand, Huang et al illustrated that BHMH (>90% selectivity) was synthesized from HMF (>90% conversion) via reductive self-coupling with metal powders (e.g., Al, Mg, or Zn) and 10% NaOH at room temperature after 6 h, and long-chain alkane (C 12 ) was obtained via subsequent dehydration/hydrogenation in water at 300 °C under 4.0 MPa H 2 after 3 h catalyzed by a metal catalyst (e.g., Pt/C or Pd/C) and a solid acid (e.g., NbOPO 4 , TaOPO 4 or ZnCl 2 ). − By using either homogeneous or immobilized N-heterocyclic carbenes (NHCs) as catalysts, Liu and Chen with co-workers conducted a series of studies on the self- and cross-coupling of HMF and FUR for the synthesis of C 10 -C 12 furoins (>90% yields). − This simple, metal-free in-air oxidation reaction process is highly promising for practical applications.…”

Thermally Regulated Recyclable Carbene Catalysts for Upgrading of Biomass Furaldehydes

“…This likely explains the lower activity toward HMF in general. In previous work when NHC was generated with a base (e.g., DBU), 20,38,39,59 acid−base chemistry between the NHC and HMF hydroxy group did not impede reactivity, suggesting that in these coupling systems, the active NHC is indeed more nucleophilic than Brønsted basic, and that the acetate must be the promiscuous species. Our initial report, which employed stoichiometric amounts of the ionic liquid [EMIM]OAc, 25 gave good yield (72%) in the presence of HMF's hydroxy proton, but this very interaction can also explain the increase in yield from 72 to 98% when a catalytic amount of Enders TPT (3,4,5-triphenyl-1,2,4-triazole) was used rather than stoichiometric [EMIM]OAc.…”

“…For instance, an NHC derived from the acetate substituted thiazolium, in combination with triethylamine base, catalyzes the self-coupling reaction of FF into C 10 furoin in quantitative selectivity and yield . NHCs derived from benzimidazolium ([BI]) salts with one or two long-chain alkyl substituents on the nitrogen atoms in the imidazole ring can even catalyze the self-coupling reaction of benzaldehyde in water. , Highly efficient and recyclable supported NHC catalyst systems based on long-chain alkyl substituted [BI] salts were also successfully developed for the self-coupling reactions of FF and HMF. − The catalyst recycling procedure involves activation of the [BI] salt (precatalyst) with a base to generate the NHC catalyst, catalysis in conversion of FF and HMF into C 10 and C 12 furoins, and recycling of the catalyst by quenching the reaction with HCl to reform the precatalyst, followed by filtration before use in the next cycle . However, for every catalysis cycle, stoichiometric amounts of base and acid are required, which not only added to the cost but also generated more waste and complicated the product separation.…”

Biocatalytic Transformation of 5-Hydroxymethylfurfural into High-Value Derivatives: Recent Advances and Future Aspects

“…BHMF, possessing one carbonyl group, two furan rings and three hydroxyl groups, is a multifunctional compound, which can be employed for the production of oxygen-containing diesels, long-chain alkanes and linear or branched polyurethanes . In terms of theory, BHMF can not be directly formed by the self-aldol condensation of HMF due to the absence of α-hydrogen atom. − However, Chen and co-workers in 2012–2016 found that two molecules of HMF could readily connect together to produce BHMF over 1-ethyl-3-methylimidazolin-2-ylidene, 1,3-dimesitylbutyl-imidazolin-2-ylidene, 3-benzyl-5-(2-hydroxyethyl)-4-methylthiazolin-5-ylidene or 1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene, a kind of N -heterocyclic carbenes that are present in the corresponding ionic liquids, via the umpolung carboligation, − which was verified to be related to the change of electrophilic carbonyl carbon into the nucleophilic center as an acyl anion equivalent (Figure ). Gratifyingly, Donnelly et al in 2015 confirmed that the umpolung carboligation of HMF could also be accomplished by means of an enzymatic system, in which thiamine-diphosphate dependent benzaldehyde lyase (BAL) from Pseudomonas fluorescens was used as a catalyst in phosphate buffer, leading to 70% yield of BHMF at RT for 18 h .…”