Two-Step Experiment for Undergraduate Organic Chemistry Laboratory Using Green Techniques: Synthesis of Acetylferrocene and Its Reduction to (±)-1-Ferrocenylethanol

Abstract

Electrophilic aromatic substitution reactions and ketone reduction are fundamental reactions in sophomore-level organic chemistry courses. One commonly taught example of electrophilic aromatic substitution in undergraduate laboratories is the Friedel–Crafts acylation of ferrocene, often carried out using acetic anhydride in the presence of concentrated phosphoric acid. Similarly, the reduction of the ketone to alcohol is performed using sodium borohydride in the presence of protic solvents. These methods typically involve hazardous chemicals and tedious workup procedures. To address these limitations and incorporate green chemistry principles, we developed a two-day experiment. On the first day, acetylferrocene is synthesized via the acetylation of ferrocene using acetyl chloride and zinc oxide in dichloromethane. On the second day, the acetylferrocene is reduced to (±)-1-ferrocenylethanol under solventless reaction conditions by grinding it with NaBH₄ and silica gel, followed by intermittent heating using a household microwave. Both reaction yields are nearly quantitative after their aqueous workup. The products are characterized by melting point, IR spectroscopy, and NMR spectroscopy. Students complete prelab assignments on the structure of ferrocene and the mechanisms of electrophilic aromatic substitution and reduction and postlab reports focused on synthesis, purification, and product characterization. This experiment enhances student learning while minimizing chemical usage, improving safety, maximizing yields, and introducing the concept of nontraditional solid-phase reactions.