Preparation of chitosan/poly(methacrylic acid) supported palladium nanofibers as an efficient and stable catalyst for He
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Ó Indian Academy of Sciences Sadhana (0123456789().,-volV)FT3](0123456 789().,-volV)
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Preparation of chitosan/poly(methacrylic acid) supported palladium nanofibers as an efficient and stable catalyst for Heck reaction SHAOFENG ZHONG Department of Jianhu, Zhejiang Industry Polytechnic College, Shaoxing 312000, People’s Republic of China E-mail: [email protected] MS received 14 February 2020; revised 14 April 2020; accepted 27 April 2020
Abstract. Homogeneous chitosan/poly(methacrylic acid) solution containing Pd2? cations was successfully prepared by addition of pyridine-2-carboxaldehyde. Then, this homogeneous solution was smoothly electrospun into uniform composite nanofibers with mean diameter of 442 ± 163 nm, followed by annealing at elevated temperature to improve the solvent resistance. Scanning electron microscopy (SEM) analysis shows that the solvent resistance of the composite nanofibers was improved with the increment of annealing temperature. FT-IR spectra demonstrate that the chemical structure of the composite nanofibers was not oxidized after annealing process. Moreover, the palladium species were homogeneously incorporated inside the composite nanofibers. The catalytic performance of these novel composite nanofibers was evaluated by Heck reaction. The catalysis result shows that these composite nanofibers were very efficient to catalyze the Heck reaction of aromatic iodides with acrylates with yields over 86%. Moreover, these composite nanofibers can be reused for 10 times with little decrement of yield. Keywords. Chitosan; palladium; Heck reaction; nanofiber; embed.
1. Introduction Palladium-catalyzed reactions have played an important role in the preparation of fine chemicals and pharmaceutically active compounds.1,2 Homogeneous palladium catalysts have attracted much attention for their high catalytic activity and selectivity, but the separation and recovery of the expensive palladium metal and ligands after reaction were comparably costly and difficult, especially for the commercial scale productions of pharmaceuticals, cosmetics and food industries.3,4 The residue of palladium in the reaction products commonly limits their further applications. Immobilization of homogeneous palladium catalyst on suitable solid matrices can greatly solve or mitigate these drawbacks.5,6 The immobilized palladium catalysts can be readily separated and recovered from the reaction mixture, which not only can reduce the cost of product, but also can minimize the waste production, resulting in a green and sustainable chemical transformation process. Generally, solid matrices with larger specific surface area were used as the supporting materials to improve the dispersion of the palladium species.7,8 *For correspondence
However, the highly porous supporting matrices are easily collapsed in the harsh reaction conditions, leading to the aggregation and leaching of palladium species. Besides the collapse of porous structure, the reduction of Pd2? cations into Pd0 species and harsh reaction conditions (e.
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