Sulfochitosan encapsulated nano-Fe3O4 as an efficient and reusable magnetic catalyst for green synthesis of 2-amino-4H-chromen-4-yl phosphonates

Highly dispersed chitosan-coated nano Fe3O4 core-shell structures (Fe3O4@CS NPs) are prepared simply through in situ co-precipitation of Fe3+ and Fe2+ ions via NH4OH in an aqueous solution of chitosan. Treatment of Fe3O4@CS NPs with chlorosulfonic acid leads to the formation of Fe3O4@CS-SO3H NPs which exerts excellent catalytic activity toward one-pot, three-component synthesis of 2-amino-4H-chromen-4-yl phosphonate derivatives. The core-shell structure and the composition of produced magnetic nanocatalyst are analyzed using FT-IR, XRD, TGA, VSM, ICP, SEM, TEM and BET. The results reveal that the unique heterogeneous Fe3O4@CS-SO3H NPs appears as an excellent acid catalyst which produces high yields, impressive turnover number (TON) and turnover frequency (TOF) values with good recyclability without significant loss of the activity. Moreover, the proposed green synthetic method takes advantage of nontoxic reagents in an aqueous media through a simple procedure. (C) 2013 Elsevier B.V. All rights reserved.