Synthesis of phosphoric acid supported on magnetic core-shell nanoparticles: a novel recyclable heterogeneous catalyst for Kabachnik-Fields reaction in water

In this paper, supported phosphoric acid on silica coated magnetic nanoparticles (gamma-Fe2O3@SiO2-PA) was synthesized as a new solid acid via the reaction of chloro-functionalized gamma-Fe2O3@SiO2 with triethyl phosphite followed by hydrolysis. The synthesized gamma-Fe2O3@SiO2-PA was characterized by SEM, HRTEM, BET, FT-IR, TGA, ICP and VSM. It was used as a magnetically recyclable heterogeneous catalyst for the efficient one-pot synthesis of alpha-aminophosphonates through Kabachnik-Fields reaction in water. Good to high yields of alpha-aminophosphonates showed that gamma-Fe2O3@SiO2-PA had strong and sufficient acidic sites, which were responsible for its catalytic performance. More importantly, the catalyst was easily isolated from the reaction mixture by a magnetic bar and reused at least five times without significant degradation in the activity.