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.
Polystyrene-grafted silica nanoparticles bearings ulfonic acid centers and with tunable amphiphilic properties were designed to perform the biphasic etherification reaction of glycerol with dodecanola tt he interface of Pickering emulsions. By optimizing the hydrophobic properties of the particles, double Pickeringe mulsions could be generated allowing af acilitated diffusion of glycerol and dodecanol into the microenvironment near the acidc enters.One of the key challenges in the design of biorefineries is how to devise green and sustainable technologiesf or the conversion of biomass into valuable chemicals in the presenceo fi mmiscible reagents.[1] In addition to solvents, external agents such as surfactants, phase-transfer agents, [2] and even surfactant-combined catalysts [3] can be used to boost the contact and transfer between reagents. However,t hese additives are difficult to recycle, hampering the green footprint of the process.Pickeringe mulsions relyingo na mphiphilic nanoparticles can be used as ap latform to perform biphasic reactions.[4] Two concepts emerge depending on the relative positionb etween the catalyst and the liquid/liquid (L/L) interface:o ne, Pickeringassistedc atalysis, which combinesn anoparticles (or polymersomes)f or emulsification with ah omogeneousc atalysto r enzymeh osted inside the emulsion droplets; [5] two, Pickeringinterfacial catalysis, where the nanoparticles behave concomitantly as solid emulsifiers and interfacial catalysts. [6] In the latter case, the particlea ssembly at the L/L interface increases not only the interfacial area between the reagents, but also alleviates external mass-transfer limitations.Recently,w es howed that organosilicas (SiNPs,N P = nanoparticle) bearing sulfonica cidg roups can behavea sa ctive and recyclable catalysts in the biphasic etherification reaction of fatty alcoholsw ith polyols, paving the way to novel biobased surfactants.[7] Nonetheless, in these industrially relevant reactions, the catalytic activity is suppressed owing to resilient diffusionalb arriers ascribed to the high viscosity of polyols (h glycerol = 815 mPa sa t3 5 8C) and to the large density difference between the phases. Herein, we show how as ubtle interplay between the amphiphilic andc atalytic properties of SiNPs can enhancet he reactivity of the glycerol/dodecanol system towardsd odecyl glyceryl ethers( DGE, h DGE = 820 MPa sa t 70 8C; Figure 1A). To this aim, we prepared as ystematic series of randomly sulfonated polystyrene-modified SiNPs (PSS@SiO 2 ) with finely tunable surface and acid properties that are able to stabilizeg lycerol/dodecanol emulsions even at high temperatures (150 8C).The PSS@SiO 2 nanoparticles were prepared over Aerosil 200 silica using af our-step protocol (see the Supporting Information for furtherd etails): one, silica hydroxylation;t wo, reaction of dry silica with [(chloromethyl)phenylethyl]trimethoxysilane (CPMS) in acetoneu nder an inert atmosphere;t hree, styrene polymerization on CPMS-grafted silicas by atom-transfer radical polym...
New rare earth perfluorooctanoates [RE(PFO) 3 ] were developed and applied to the condensation reactions of indole with carbonyl compounds at ambient temperature. It was found that these catalysts could be completely recovered and reused without loss of catalytic activities.
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