Sustainable synthesis of magnetically separable SiO^sub 2^/Co@Fe^sub 2^O^sub 4^ nanocomposite and its catalytic applications for the benzimidazole synthesis

The Co(II) and Fe(III) centres magnetically separable two new mesoporous nanocatalyst were synthesised via chemical synthesis method. The transmission electron microscopic studies (TEM) show that, the particles are spherical shape with mean size of 20 nm. The Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) reveals that SiO2 is coating on the surface of the cobalt ferrate nanoparticle (CoFe2O4). The SiO2 coating is efficiently preventing the aggregated collision of nanoparticles. Magnetic measurements show that diamagnetic character of the SiO2 is unaffected to the coercivity of SiO2 coated CoFe2O4 particles. In addition, these nanoparticles are used as nanocatalyst for high yielding, facile and expeditious synthesis of various functionalized 2-arylbenzimidazoles via one-pot condensation. The cascade including imine formation, cyclization, condensation, and aromatization occurs, without addition of any reducing or oxidizing agents. In all situations, the desired product was synthesised with excellent yield. The shorter reaction time, mild reaction condition, simplicity, non-toxicity, safe reaction and easy workup are the impotent merits of this protocol.Statement of SignificanceIn SiO2 coated CoFe2O4 particles SiO2 serves as an efficient capping agent and prevent the aggregation of nanoparticles hence reducing the particle size, this cascade open up with stoichiometric quantity of using SiO2 with unaffected ferromagnetism of CoFe2O4 particles along with reducing the particle size. In addition SiO2 coated CoFe2O4 particles act as a highly efficient nanocatalytic, this method can be extended to the development of other catalytic system used in the synthesis of important pharmacological drungs. Moreover this catalyst employed economic large scale synthesis of cyclization reaction with recoverable and reusable properties without loss of catalytic activity for several cycles.