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

In 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 Fe 3 O 4 with a particle size of about 10 nm was performed with the silane coupling agent of vinyl triethoxysilane (SG-151) to obtain Fe 3 O 4 with carbon–carbon double bonds on the surface (SG-Fe 3 O 4 ). Subsequently, SG-Fe 3 O 4 , styrene (St) and chloromethyl styrene (CMSt) were polymerized to obtain the magnetic chloromethylated polystyrene sphere (SG-Fe 3 O 4 @PS-Cl) with core-shell structure by solution copolymerization. Using St as monomer and SG-Fe 3 O 4 @PS-Cl as macromolecular initiator, the magnetic polystyrene brush of SG-Fe 3 O 4 @PS-PSt was obtained by activated regenerated electron transfer catalyst atom transfer radical polymerization. Finally, SG-Fe 3 O 4 @PS-PSt was sulfonated with sulfuric acid to form a magnetic sulfonated polystyrene brush of SG-Fe 3 O 4 @PS-PSH. SG-Fe 3 O 4 @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-Fe 3 O 4 @PS-PSH was better than p-toluenesulfonic acid and commercial macroporous sulfonic acid resin. The external magnetic field can directly recover SG-Fe 3 O 4 @PS-PSH, simplifying the recovery of catalyst and reducing the catalyst loss. After recycling, the yield of ethyl N-phenylformimidate was not significantly decreased.