New Dihydroxyacetophenone‐Based Vanadyl(IV) Complex Anchored to Fe ₃ O ₄ as a Catalyst for Benzoxazole Production: Investigating the Kinetic Parameters

ABSTRACT The dihydroxyacetophenone (DHAP) ligand was anchored on Fe 3 O 4 NPs, and its vanadyl(IV) complex was synthesised. This catalyst was investigated by different techniques of FT‐IR, XRD, XPS, TEM, FESEM, TGA, ICP‐OES, EDX, DLS, BET and TGA. Benzoxazoles were synthesised in high yields using 3,5‐di‐ tert ‐butyl catechol (0.5 mmol), ammonium acetate (0.5 mmol), aldehydes (0.5 mmol), solvent (ethanol 5 mL) and heterogeneous homogeneous catalyst (0.18 mol%). Benzoxazoles were synthesised in mild conditions of ambient temperature in an ethanol solvent under air oxygen for 3 h. This efficient oxidative cyclisation reaction suggests that the catalyst is bi‐active system due to the presence of two active centres of redox‐active vanadyl(IV) group for oxidative transformation and uncoordinated free hydroxyl groups on the DHAP ligand. These last groups can affect the dispersibility of the catalyst in solvent via hydrogen bonding. Moreover, they gather catechol, aldehyde and acetate substrate on catalyst surface and help vanadyl(IV) centre in substrate activation via proton shuttling to faciliate reaction. The catalyst was reused for six consecutive cycles with no significant loss in performance. The product yield in the sixth cycle was 87%. A hot filtration test confirmed the catalyst's stability and heterogeneous nature. The kinetic analysis of benzoxazole production was conducted using the spectrofluorimetric technique. This catalysis in molecular liquid provides insight into molecular interactions at the solution/catalyst interphase. The activation parameters of enthalpy, entropy and rate constants at different temperatures were obtained. The activation parameters of enthalpy ∆H ≠ = 1.67 × 10 4 kJ mol −1 , entropy ∆S ≠ = −193.01 kJ mol −1 and rate constant of 0.7140 k (mol 3 L −3 min −1 ) at 30°C were also obtained.