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Biopolymers as Supports for Heterogeneous Catalysis: Focus on Chitosan, a Promising Aminopolysaccharide
Published in Arup K. SenGupta, Ion Exchange and Solvent Extraction, 2007
Eric Guibal, Thierry Vincent, Francisco Peirano Blondet
Chitosan has been used as a support for carbonylation reactions.365,396,397 Zhang and Xia studied the effect of hydroesterification of olefins in the presence of CO and alcohol for the synthesis of carboxylic esters.365 They prepared bimetallic catalysts supported on chitosan for the carbonylation of 6-methoxy-2-vinylnaphtalene to esters of naproxen (a nonsteroidal antiinflammatory drug). Palladium chloride is mixed with 4 M HCl:ethanol solution (1:19 v/v). The solution is mixed with a SiO2-chitosan support (prepared by the precipitation-drying procedure) under reflux. The carbonylation of 6-methoxy-2-vinylnaphtalene is operated under CO atmosphere, at fixed temperature, in the presence of triphenylphosphine (PPh3), HCl, methanol, dioxane, and biphenyl, and a second metal chloride salt. The reaction leads to the formation of three different products (Figure 4.46): the methyl ester of naproxen, its linear isomer [methyl 3-(6-methoxy-2-naphtyl] propanoate), and the product of the etherification reaction of methanol with α-(6-methoxy-2-naphtyl) ethanol. Compared to more conventional materials (PdCl2/NiCl2, alone or combined with polyvinylpyrrolidone, used as a stabilizer of Pd/Ni nanoparticles), the conversion yields remain comparable, while the selectivity for ester of naproxen is strongly increased for chitosan-supported material. The reaction is controlled by the temperature (optimum at 100°C), the pressure of CO (optimum at 40 bar), the presence of an acid promoter (0.8 M HCl), the solvent (methanol is preferred), and the type of second metal (Ni, with molar ratio Ni:Pd close to 2). The addition of triphenylphosphine to the reactive media contributes to palladium stabilization and to preventing the formation of inactive bulk Pd particles (the optimum molar ratio between PPh3 and Pd is close to 3). The production yield reaches 96% with regioselectivity greater than 95%. The same reaction is tested with styrene (and various derivatives). Zhang and Xia concluded that the catalyst is more efficient and more selective for styrene than for its derivatives.365 The selectivity and the stability of the catalyst are significantly improved by the addition of p-benzoquinone, due to its protective effect against aggregation of Pd particles. Hydroesterification of vinylnaphtalene derivative.
Electrodeposition of Pd from a deep eutectic solvent system: effect of additives and hydrodynamic conditions
Published in Transactions of the IMF, 2019
DES solutions were prepared by mixing of choline chloride (ChCl) (Sigma, 98%) with urea (UA) (AppliChem, 99%) in a molar ratio of 1:2. The mixtures (DES) were processed under partial vacuum at 80°C for 3 h to remove traces of ammonia/amines and to reduce the moiety of water in the solutions. Palladium (Pd) was introduced to the basic solutions by dissolution of palladium chloride (PdCl2-anhydrous, Alfa Aesar, 99.9%) at 70°C to result in orange-red coloured [PdCl4]2− solutions. To study the effect of additives on palladium deposition, 2.4 mmol L−1 of 2-formyl-benzenesulphonic acid salt (BFS) (C7H5NaO4S), saccharin (SAC) (C7H5NO3S), 5-sulphosalicylic acid dehydrate (SSS) (C7H6O6S), sodium benzene-1,3-disulphonate (NBDS) (C6H4Na2O6S2), naphthalene-1,3,6-trisulphonic acid (NTSA) (C10H7Na3O10S3) or nicotinic acid amide (NA) (C6H6N2O) was added to the basic Pd electrolyte. In Figure 1 a simplified molecular structure is given for the organic compounds used with their different functional groups (e.g. hydroxyl-, amide- or sulphonate group).