Silica coated magnetic Fe3O4 nanoparticles supported phosphotungstic acid: a novel environmentally friendly catalyst for the synthesis of 5-ethoxymethylfurfural from 5-hydroxymethylfurfural and fructose

In this study, a magnetically-recoverable catalyst (Fe3O4@SiO2-HPW) was prepared by the application of phosphotungstic acid (HPW) supported on silica-coated Fe3O4 nanoparticles. The prepared samples were characterized by XRD, TEM, FT-IR, and N-2-adsorption-desorption isotherms. The content of W in Fe3O4@SiO2-HPW was measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and its surface acidity was determined by a potentiometric titration with n-butylamine. Fe3O4@SiO2-HPW showed an excellent catalytic activity for the synthesis of EMF from HMF and fructose. Under optimal reaction conditions, EMF was obtained in a high yield of 83.6% by the etherification of 5-hydroxymethylfurfural. EMF could also be synthesized directly from fructose in a yield of 54.8% via a one-pot reaction strategy. After reaction, the catalyst Fe3O4@SiO2-HPW could be easily separated from the reaction mixture with an external magnetic field, and it could be reused at least five times without any loss of its catalytic activity.