Putting the squeeze on imine synthesis: citrus juice as a reaction medium in the introductory organic laboratory

ABSTRACT A less hazardous and energy efficient reaction performed using freshly squeezed citrus juice as solvent has been designed and implemented within a sophomore level organic chemistry laboratory. The primary learning objectives are to enable students to (i) identify and reflect upon various green chemistry principles such as waste prevention, atom economy, less hazardous synthesis, use of safer chemicals, catalysis, design for energy efficiency, and inherently safer chemistry for accident prevention; (ii) use proton NMR spectroscopic data to characterize a synthesized Schiff base (imine); and (iii) describe the reaction mechanism for imine formation, including the reasoning for why citrus juice is an excellent reaction medium. Specifically, 4-nitrobenzaldehyde is combined with 4-methoxyaniline at room temperature in the presence of four different fruit juices as reaction media to successfully synthesize an imine that is expensive to procure commercially. This is followed by students undertaking reduction of the imine to form a secondary amine which has a dramatically distinct color due to the disruption in conjugation. In performing this overall reductive amination, students expand their knowledge on acid-catalyzed imine synthesis and its mechanism, strengthen their practical skills in the laboratory, and reflect on green chemistry principles within the context of fundamental organic reactivity. GRAPHICAL ABSTRACT