Microwave-Assisted, Solvent-Free Synthesis of Benzothiazoles Using a Bimetallic Fe–Al/Silica Heterogeneous Catalyst

Objective: Green chemistry emphasizes the development of efficient, sustainable, and environmentally friendly catalytic systems. The present study aimed to design and evaluate a bime-tallic Fe–Al/silica heterogeneous catalyst for the microwave-assisted, solvent-free synthesis of ben-zothiazoles, addressing the limitations of conventional homogeneous and monometallic catalytic systems. Methods: The Fe–Al/silica catalyst was prepared by co-impregnation of Fe and Al precursors onto silica, followed by calcination. Its structural and morphological characteristics were analyzed using XRD, FT-IR, SEM, and EDS. Catalytic performance was assessed by the condensation of 2-ami-nothiophenol with aldehydes under microwave irradiation. Reaction parameters, including temper-ature, catalyst loading, and microwave power, were optimized. Comparative studies were per-formed against bare silica, monometallic, bimetallic, and homogeneous catalysts. Catalyst recycla-bility was evaluated through repeated cycles and hot-filtration tests. Results: Under optimized conditions (560 W, 120℃, 1.18 mol% catalyst), the Fe–Al/silica catalyst achieved up to 95% yield of benzothiazoles within 5 minutes, significantly outperforming control catalysts. The synergistic interaction of Fe (redox activity) and Al (Lewis acidity), uniformly dis-persed on silica, was identified as the key factor for enhanced activity and selectivity. The catalyst maintained >90% activity over seven reuse cycles with negligible leaching (<0.5% by ICP analy-sis). Discussion: The study highlights the superiority of Fe–Al/silica over conventional homogeneous salts (FeCl₃, AlCl₃) and other supported systems, owing to its high surface area, dual functional sites, and efficient microwave absorption. The cooperative effect between Fe and Al enhances cat-alytic efficiency while ensuring recyclability, aligning with green chemistry principles. Conclusion: This work demonstrates, for the first time, the efficiency of a recyclable Fe–Al/silica heterogeneous catalyst for solvent-free, microwave-assisted synthesis of benzothiazoles. The method offers rapid reaction times, high yields, energy efficiency, and environmental safety, providing a promising green alternative for heterocyclic synthesis.