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

KEYWORDS:

• Second-year undergraduate
• laboratory instruction
• green synthesis
• organic chemistry
• reaction mechanisms
• catalysis
• NMR spectroscopy

Acknowledgements

We are grateful to the Department of Chemistry at the University of Toronto for their financial support through the Chemistry Teaching Fellowship Program, and to the University of Pittsburgh for a Mascaro Grant. Special thanks to Loise Perruchoud (UT), Bret Tantorno (UPJ) and Azariah Arthur (UPJ) who contributed to the preparation and execution of this laboratory experiment, and to the participating undergraduate students (UT and UPJ) and graduate student teaching assistants (UT) for their invaluable feedback.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by University of Toronto and University of Pittsburgh.