Sulfonated polystyrene brushes grafted onto magnetic nanoparticles as recoverable catalysts for efficient synthesis of ethyl N‐phenylformimidate

Abstract

AbstractIn this work, the sulfonated polystyrene brushes were grafted onto magnetic nanoparticles to obtain recoverable catalysts for efficient synthesis of ethyl N‐phenylformimidate. First, the surface modification of Fe3O4 with a particle size of about 10 nm was performed with the silane coupling agent of vinyl triethoxysilane (SG‐151) to obtain Fe3O4 with carbon–carbon double bonds on the surface (SG‐Fe3O4). Subsequently, SG‐Fe3O4, styrene (St) and chloromethyl styrene (CMSt) were polymerized to obtain the magnetic chloromethylated polystyrene sphere (SG‐Fe3O4@PS‐Cl) with core‐shell structure by solution copolymerization. Using St as monomer and SG‐Fe3O4@PS‐Cl as macromolecular initiator, the magnetic polystyrene brush of SG‐Fe3O4@PS‐PSt was obtained by activated regenerated electron transfer catalyst atom transfer radical polymerization. Finally, SG‐Fe3O4@PS‐PSt was sulfonated with sulfuric acid to form a magnetic sulfonated polystyrene brush of SG‐Fe3O4@PS‐PSH. SG‐Fe3O4@PS‐PSH was used as a recoverable acid catalyst to synthesize ethyl N‐phenylformimidate. Due to the high loading of the sulfonic acid group of this catalyst, its added amount was lower than other solid acids such as p‐toluenesulfonic acid. The results showed that the catalytic performance of SG‐Fe3O4@PS‐PSH was better than p‐toluenesulfonic acid and commercial macroporous sulfonic acid resin. The external magnetic field can directly recover SG‐Fe3O4@PS‐PSH, simplifying the recovery of catalyst and reducing the catalyst loss. After recycling, the yield of ethyl N‐phenylformimidate was not significantly decreased.