A new and green synthesis of formamidines by γ-Fe2O3@SiO2–HBF4 nanoparticles as a robust and magnetically recoverable catalyst

A series of Brønsted acids (HA) were immobilized on superparamagnetic γ-Fe2O3@SiO2. The synthesized [γ-Fe2O3@SiO2–HA] nanocrystallites were fully characterized by spectroscopic techniques (FT-IR, XRD, SEM, EDX) and used as solid acid catalysts in the synthesis of biologically important formamidines. The results were excellent in yield and time of reaction. Activity of various Brønsted acids on superparamagnetic support as catalyst were also evaluated and among them immobilized HBF4 showed the best catalytic properties.