TEMPO Synthesis, Characterization and Catalysis: An Integrated Upper-Division Laboratory

Abstract

We report an undergraduate, upper-division laboratory based on the synthesis of a stable, persistent organic free radical, TEMPO (2,2,6,6 tetramethylpiperidine-1-oxyl), and its characterization by electron paramagnetic resonance (EPR) and cyclic voltammetry (CV). The synthesis involves a three-electron oxidation of 2,2,6,6-tetrametylpiperidine by tungstate-catalyzed activated hydrogen peroxide. Students characterized their TEMPO by CV in our department, and we visited the University of Denver for the EPR characterization. Additionally, the TEMPO-catalyzed oxidation of a primary alcohol to the carboxylic acid in the presence of co-oxidants sodium hypochlorite and sodium chlorite was also investigated. This lab uniquely integrates key concepts and principles from both organic and physical chemistry, providing a comprehensive learning experience in upper-division instructional laboratories. This undergraduate lab is particularly relevant now, as the TEMPO radical is being used for the determination of local oxygen concentration in tumors, changes in redox status and radiation damage in cells, and in new battery technology. The four-part laboratory allows the flexibility of offering it in sophomore organic chemistry, physical/analytical chemistry laboratories or as an independent project for junior/senior level students over a 4-week period. Additionally, the four-part laboratory allows the flexibility of offering it in second-semester organic, physical, and/or analytical chemistry laboratories. Ultimately, this should serve as exemplary model for collaboration and cooperation between faculty at different universities with limited instrumentation.