Microwave-assisted Cr2O3 nanoparticle-catalyzed synthesis of 2-amino-4H-chromenes: evaluation of antioxidant, corrosion inhibition, and molecular docking studies

In this study, chromium(III) oxide (Cr₂O₃) nanoparticles were prepared through a green synthesis route using Hamelia patens leaf extract. The naturally occurring phytochemicals in the extract acted both as reducing agents to convert the chromium precursor and as stabilizing agents to prevent agglomeration. The nanoparticles were examined using UV–Vis spectroscopy, FTIR, XRD, SEM–EDX, DLS, and zeta potential analysis. These techniques confirmed their crystalline nature on the nanoscale, spherical particle morphology, the presence of surface-bound biomolecules, and stable colloidal dispersion. The biosynthesized nanoparticles were then employed as catalysts in a one-pot multicomponent reaction to obtain 2-amino-4H-chromene derivatives. Reaction optimization showed that the catalyst produced consistently high yields under mild reaction conditions, surpassing the performance of conventional organocatalysts. The antioxidant properties of the chromene derivatives (5a–5e) were assessed by the DPPH assay in methanol, ethyl acetate, and acetone, revealing notable solvent-dependent variations in radical scavenging activity. Among the tested compounds, 5b, derived from 9-anthracenecarboxaldehyde, displayed more than 95% radical scavenging activity in acetone. In addition, electrochemical impedance spectroscopy (EIS) was used to study the corrosion-inhibition behaviour of the most active chromenes on mild steel in acidic medium. Compound 5a achieved the highest inhibition efficiency of 85.46% at a concentration of 200 ppm, as confirmed by Nyquist, Bode, and Tafel analyses.

Graphical abstract