Modified Halloysite Nanotubes for the Efficient Synthesis of Spirooxindoles and 1,2,4‐Triazolidine‐3‐Thiones (Ones)

ABSTRACT A recoverable magnetic nanocatalyst based on halloysite nanotubes (HNTs) was synthesized by functionalizing them with L‐arginine, followed by immobilization of a heteropoly acid (HPA). The composite was characterized using various analytical techniques, including FT‐IR spectroscopy, thermogravimetric analysis (TGA), X‐ray diffraction (XRD), scanning electron microscopy with energy‐dispersive X‐ray spectroscopy (SEM‐EDS), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), CHN elemental analysis, inductively coupled plasma optical emission spectroscopy (ICP‐MS), Brunauer–Emmett–Teller (BET) surface area analyses, and dynamic light scattering (DLS). The catalytic efficiency of [HNTs‐Arg@Fe 3 O 4 @HPA] was evaluated in the synthesis of biologically active functionalized spirochromene and 1,2,4‐triazolidine‐3‐thione (one) derivatives. Compared to the unsupported HPA, the synthesized nanocatalyst exhibited superior catalytic activity in the studied reactions. These reactions displayed high product yields at room temperature using a water:ethanol solvent mixture (9:1 ratio). The nanocatalyst could be easily recovered and reused for at least five consecutive cycles without a significant loss in activity or selectivity. Phenyl‐1,2,4‐triazolidine‐3‐thione derivatives (7l–m and 7s–w) were synthesized and evaluated for their antibacterial activity as part of efforts to discover novel antibacterial agents. The results indicated that some of the newly synthesized 1,2,4‐triazolidine‐3‐thione derivatives are promising candidates for further investigation as antibacterial agents. The introduced nanocatalyst appears promising as a useful catalyst for organic transformations.