Deriving the Turnover Frequency of Aminoxyl-Catalyzed Alcohol Oxidation by Chronoamperometry: An Introduction to Organic Electrocatalysis

Abstract

Organic electrosynthesis is an increasingly popular tool for driving and probing redox reactions. Recent advances in this field often employ an electrocatalyst to enhance the selectivity and efficiency of electrochemical reactions. A laboratory experiment was developed to introduce students to relevant mechanistic techniques in electrochemistry for analysis of electrocatalytic reactions using aminoxyl-catalyzed alcohol oxidation as a case study. This lab activity employs cyclic voltammetry for qualitative assessment of catalytic turnover prior to introducing students to chronoamperometry, an underutilized technique that facilitates quantitative determination of the rate of catalysis. Students identify and rationalize the important features of a reversible electron transfer and a catalytic reaction in a cyclic voltammogram, probe the origin of scan rate effects on these traces, and calculate turnover frequency using a series of chronoamperograms. The method employs safe and readily available reagents: basic aqueous buffer solution, alcohol substrate, and an inexpensive organic aminoxyl catalyst. Student data presented herein were obtained from a course attended by undergraduate students, graduate students, and pharmaceutical chemists.

A Practical Oxidation Experiment for Undergraduate Students: Bobbitt’s Salt as a “Green” Alternative

“…In considering this disconnect, oxoammonium cations are uniquely poised to serve as modern oxidizing agents in the undergraduate laboratory, possessing significant advantages with regard to green chemistry, practicality, and modularity with respect to didactic aim. Realizing the suitability of related nitroxides for the undergraduate instructional laboratory setting, Hill, Hoover, and Stahl reported a copper-catalyzed oxidation of benzylic alcohols mediated by TEMPO and, more recently, an electrochemical variant of the experiment . The introduction of this chemistry to undergraduates was, and continues to be, a significant advance in educating students about aspects of green chemistry.…”

“…In addition to being advantageous pedagogically, Bobbitt’s salt has many of the desirable attributes discussed by prior “green” undergraduate experiments. − The reagent itself is derived from 4-amino-2,2,6,6-tetramethyl­piperidine (a cheap tetramethyl­piperidinyl variant produced from acetone and ammonia) and can be prepared in aqueous media. , It has been commercialized and can be purchased from an array of vendors (at ∼$6 per gram) or prepared in house (∼$0.50 per gram) . The physical properties of the oxidant make it an ideal reagent for the undergraduate laboratory setting.…”

Why Is Voltammetric Current Scan Rate Dependent? Representation of a Mathematically Dense Concept Using Conceptual Thinking

“…This 3 h activity/workshop was introduced to 28 students: upper-level undergraduate students in a physical chemistry laboratory course, undergraduate research students, and first year graduate students. For the physical chemistry laboratory, the students had basic knowledge of electrochemistry by doing a voltammetric study of TEMPO redox and catalysis reactions, or by analyzing the previously collected results when they had no access to a laboratory . The graduate and undergraduate research students had interest in electrochemistry and cyclic voltammetry for their research projects and had basic knowledge of CV by reading through refs and .…”

Constant Potential and Constant Current Electrolysis: An Introduction and Comparison of Different Techniques for Organic Electrosynthesis

“…The oxidation potential of 1 was measured as 0.55 V (vs Fc/Fc + ) by CV. To perform the 3-electrode CPE, the potential of the working electrode (a Pt mesh) was set at 0.7 V (vs Fc/Fc + ) for bulk electrolysis, slightly more positive than the oxidation peak potential measured by CV. , As shown in Figure b (black trace), the current decays during the consumption of 1 , the only electroactive species at this applied potential. The accumulated charge is also displayed as Faraday/mol (red trace in Figure b) and reflects the consumption of 2e – per molecule .…”