Floryan De Campo

8-Aminoquinoline: A Powerful Directing Group in Metal-Catalyzed Direct Functionalization of CH Bonds

Chelate me if you can: Over the last decade, strategies for the functionalization of both C(sp2)-H and C(sp3)-H bonds have witnessed an increasing use of a simple, yet powerful directing group, 8-aminoquinoline (in blue). This auxiliary is very efficient in a wide range of metal-mediated reactions, and can be readily removed to afford the desired carboxylic acids or corresponding derivatives.

Pickering Interfacial Catalysis for Biphasic Systems: From Emulsion Design to Green Reactions

Pickering emulsions are surfactant-free dispersions of two immiscible fluids that are kinetically stabilized by colloidal particles. For ecological reasons, these systems have undergone a resurgence of interest to mitigate the use of synthetic surfactants and solvents. Moreover, the use of colloidal particles as stabilizers provides emulsions with original properties compared to surfactant-stabilized emulsions, microemulsions, and micellar systems. Despite these specific advantages, the application of Pickering emulsions to catalysis has been rarely explored. This Minireview describes very recent examples of hybrid and composite amphiphilic materials for the design of interfacial catalysts in Pickering emulsions with special emphasis on their assets and challenges for industrially relevant biphasic reactions in fine chemistry, biofuel upgrading, and depollution.

Tunable Catalysts for Solvent-Free Biphasic Systems: Pickering Interfacial Catalysts over Amphiphilic Silica Nanoparticles

Stabilization of oil/oil Pickering emulsions using robust and recyclable catalytic amphiphilic silica nanoparticles bearing alkyl and propylsulfonic acid groups allows fast and efficient solvent-free acetalization of immiscible long-chain fatty aldehydes with ethylene glycol.

Combination of Pd/C and Amberlyst-15 in a single reactor for the acid/hydrogenating catalytic conversion of carbohydrates to 5-hydroxy-2,5-hexanedione

Here we show that combination of Pd/C and Amberlyst-15 in a single reactor allowed fructose and inulin to be converted to 5-hydroxy-2-5-hexanedione, a valuable chemical platform, in a one-pot process.

Palladium/Carbon Dioxide Cooperative Catalysis for the Production of Diketone Derivatives from Carbohydrates

The one-pot production of industrially valuable diketone derivatives from carbohydrates is achieved through a bifunctional catalytic process. In particular, Pd/C-catalyzed hydrogenation of HMF in water and under CO2 affords 1-hydroxypentane-2,5-dione with up to 77% yield. The process is also eligible starting from fructose and inulin, affording 1-hydroxyhexane-2,5-dione with 36% and 15% yield, respectively. The key of the process is reversible in situ formation of carbonic acid, which is capable of assisting Pd/C during the hydrogenation reaction by promoting the dehydration of carbohydrates and the ring-opening of furanic intermediates. Interestingly, by changing the reaction medium from H2 O to a H2 O/THF mixture (1:9), it is possible to switch the selectivity of the reaction and to produce 2,5-hexanadione with 83% yield. Within the framework of sustainable chemistry, reactions presented in this report show 100% carbon economy, involve CO2 to generate acidity, require water as a solvent, and are conducted under rather low hydrogen pressures (10 bar).

Selective oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran over intercalated vanadium phosphate oxides

The selective oxidation of 5-hydroxymethylfurfural (5-HMF) to 2,5-diformylfuran (DFF) was studied over vanadium phosphate oxide (VPO)-based heterogeneous catalysts in the liquid phase. The selectivity to DFF was highly increased when using intercalated vanadium phosphate oxides under mild conditions (1 atm of oxygen, 110 °C) in an aromatic solvent. We found that the length of the intercalated ammonium alkyl chain had no clear influence on the catalytic performances, and a maximum yield of 83% could be achieved over C14VOPO4 and C14VOHPO4 after 6 h of reaction. Recycling of the catalyst was successfully performed, and we further obtained some insights in the reaction pathway: while the desired oxidation reaction indeed proceeded over the catalyst, the formation of by-products was linked to the presence of free radicals in solution.

Selectivity enhancement in the aqueous acid-catalyzed conversion of glucose to 5-hydroxymethylfurfural induced by choline chloride

In this work we wish to show that choline chloride (ChCl), a cheap and safe quaternary ammonium salt industrially produced at a few thousand tons per year through a 100% atom economy process, is capable of enhancing the selectivity of metal chlorides such as AlCl3, FeCl3 and CuCl2 in the aqueous tandem isomerization/dehydration of glucose to HMF. Under optimized conditions, 70% yield of HMF was obtained in a water/methylisobutylketone (MIBK) biphasic system which is a competitive yield to those traditionally obtained in imidazolium-based ionic liquids in the presence of hazardous chromium salts. By means of counter experiments, we show that the selectivity enhancement is optimal for a ChCl content of 50 wt% in water. At higher loading of ChCl, strong molecular interaction occurs between ChCl and HMF making the extraction of HMF from the aqueous phase difficult with MIBK, thus enhancing side reactions of HMF with water and hexoses to unwanted products. Interestingly, this process can be transposed to the direct conversion of cellulose to HMF which is an even more challenging reaction. In this case, we show that combination of FeCl3 with AlCl3 allowed cellulose to be converted to HMF with 49% yield in a one pot reaction. From the viewpoint of sustainable chemistry, this work shows noticeable advantages such as the use of (1) water as a solvent, (2) ChCl as a cheap and safe additive, (3) cheap and naturally abundant metals (Al, Fe, and Cu) and (4) renewable raw materials.

Pickering Interfacial Catalysts for solvent-free biomass transformation: Physicochemical behavior of non-aqueous emulsions

A key challenge in biomass conversion is how to achieve valuable molecules with optimal reactivity in the presence of immiscible reactants. This issue is usually tackled using either organic solvents or surfactants to promote emulsification, making industrial processes expensive and not environmentally friendly. As an alternative, Pickering emulsions using solid particles with tailored designed surface properties can promote phase contact within intrinsically biphasic systems. Here we show that amphiphilic silica nanoparticles bearing a proper combination of alkyl and strong acidic surface groups can generate stable Pickering emulsions of the glycerol/dodecanol system in the temperature range of 35-130°C. We also show that such particles can perform as Pickering Interfacial Catalysts for the acid-catalyzed etherification of glycerol with dodecanol at 150°C. Our findings shed light on some key parameters governing emulsion stability and catalytic activity of Pickering interfacial catalytic systems. This understanding is critical to pave the way toward technological solutions for biomass upgrading able to promote eco-efficient reactions between immiscible organic reagents with neither use of solvents nor surfactants.

Silica-immobilized Aquivion PFSA superacid: application to heterogeneous direct etherification of glycerol with n-butanol

We report the effective heterogenization of polymeric perfluorosulfonic acid (PFSA) Aquivion® resin in a silica network for the direct etherification of glycerol with aliphatic n-butanol. The Aquivion-silica composites, prepared by a template-free sol–gel method, presented a large specific surface area, affording highly accessible acid sulfonic groups. The textural and bulk/surface properties of the hybrid composites were characterized in-depth using TGA, acid–base titration, N2 adsorption–desorption, XRD, TEM, FTIR, Raman, CP-MAS NMR and XPS. The Aquivion-silica composites exhibited a high catalytic activity (91% n-butanol conversion) and selectivity (45% butyl glyceryl monoether yield) while they lowered the formation of by-product (6% dibutyl ether yield) as compared to benchmark homogeneous and heterogeneous acid catalysts. The catalyst was reusable and maintained a stable performance after six consecutive cycles.

Preparation of bio-based surfactants from glycerol and dodecanol by direct etherification

In this paper, we studied an original synthetic strategy to prepare bio-based surfactants by direct solvent-free etherification of glycerol with dodecanol using heterogeneous interfacial acidic catalysts dubbed Pickering Interfacial Catalysis. The conversion of dodecanol could be achieved to 60–71% with limited production of didodecyl ether (DE) as the main side product. The selectivity of the final product, alkylpolyglycerylether (AGEM), could be pushed to >80% with a water removal process at 150 °C, as a mixture of monolauryl polyglyceryl ethers, multilauryl polyglyceryl ethers and multilauryl cyclicpolyglyceryl ethers. AGEM could be isolated with a suitable work-up and was fully characterized by GC (MS), HPLC, SFC/HRMS, etc. The physicochemical properties of these new surfactants were evaluated, as well as their laundry performances. This solvent-free direct etherification process paves the way towards new value-added applications of glycerol.