SO3H@carbon powder derived from waste orange peel: An efficient, nano-sized greener catalyst for the synthesis of dihydropyrano[2,3-c]pyrazole derivatives.

• OPC-SO 3 H powder was prepared via pyrolysis and sulfonation of waste orange peels. • Characterization of OPC-SO 3 H exhibits the powder as nano-sized amorphous material. • OPC-SO 3 H acts as effective greener catalyst for dihydropyranopyrazoles synthesis. • Recyclability of OPC-SO 3 H catalyst offers 7 runs without loss of efficiency. • OPC-SO 3 H affords easy separation, metal-free, non-toxic, eco-friendlier route. Carbon nano/micro powder provides an innovative approach in the field of green catalysis by enhancing its efficiency and reusability for several chemical transformations. In this present work, we have developed an improved, forthright, highly efficient waste orange peel derived carbon (OPC) powder incorporated with sulfonic acid (OPC-SO 3 H) as a greener, highly efficient and reusable catalyst for the facile synthesis of dihydropyrano[2,3- c pyrazole derivatives via one pot four component strategy. The prepared OPC-SO 3 H powder was characterized by FT-IR, XRD, SEM, EDX, DLS-particle size, Zeta potential, TGA-DTA, BET and XPS binding studies, all the analytical techniques revealed the structural properties of prepared OPC-SO 3 H carbon powder. Especially, DLS analysis showed the OPC-SO 3 H particle size between 300 to 400 nm. A Zeta potential of −21.1 mV indicated its moderate stability and TGA/DTA studies exemplifies the thermal decomposition pattern of OPC-SO 3 H. BET studies indicate the surface textural properties of OPC & OPC-SO 3 H and the decrease in specific surface area, porous structure of OPC-SO 3 H which clearly reveals the permeability of the sulfonic acid moieties into it. XPS studies demonstrated that the binding energies of Carbon = 283.6 eV, Sulfur = 168.5 eV and Oxygen = 581.15 eV atoms confirms the presence of -SO 3 H groups along with carbon powder. The prepared OPC-SO 3 H powder act as an efficient catalyst for the synthesis of dihydropyrano[2,3- c pyrazole derivatives via multicomponent reactions. The catalytically synthesized compounds were characterized by FT-IR, 1H NMR and 13C NMR techniques. Use of recyclable OPC-SO 3 H powder catalyst for the excellent yields with rapid conversion of the targeted dihydropyrano[2,3- c pyrazole derivatives with simple work-up procedure is the notable advantage of this protocol. [ABSTRACT FROM AUTHOR]