Preparation of a Ni–ascorbic acid MOF as a recyclable catalyst for the synthesis of sulfoxides and tetrazoles†

This study introduces a novel, cost-effective, and environmentally friendly approach for synthesizing a heterogeneous Ni–ascorbic acid metal–organic framework (Ni–ascorbic acid MOF) catalyst via a hydrothermal method. The catalyst was prepared by combining nickel nitrate (Ni(NO₃)₂·6H₂O) and ascorbic acid (C₆H₈O₆) in DMF. Comprehensive characterization of the synthesized Ni–ascorbic acid MOF was performed using FT-IR, XRD, EDX, BET, SEM, TGA/DSC, and AAS techniques. These analyses revealed that the catalyst exhibits a spherical microsphere morphology with high crystallinity, a specific surface area of 16.62 m² g⁻¹, a pore diameter of 19.52 nm, and excellent thermal stability. The catalytic performance of Ni–ascorbic acid MOF was investigated in two distinct reactions, including the selective oxidation of sulfides to sulfoxides and the synthesis of 5-substituted 1H-tetrazoles. Under optimized reaction conditions, the catalyst demonstrated high efficiency with product yields ranging from moderate to excellent across various substrates. Furthermore, the catalyst exhibited remarkable recyclability, maintaining its activity over five consecutive cycles without significant leaching of nickel species, as confirmed by hot filtration tests. These findings underscore the potential of a Ni–ascorbic acid MOF as a sustainable and robust catalyst for diverse organic transformations.