Mechanistic Study of the Electrocatalytic Oxidation of Alcohols by TEMPO and NHPI

Abstract

Kinetic studies and optimization are of interest as essential steps in the field of catalysis. We performed a complementary study of the electrocatalytic performances of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) and N-hydroxyphthalimide (NHPI) towards alcohol oxidation by using voltammetry as a versatile and informative technique. Both organocatalysts exhibited a good and well-defined electrocatalytic activity in aqueous solution. Investigations of the efficacy of the reaction conditions revealed that the catalytic performance is greatly affected by the pH of the solution-and that there is a fundamental difference in reactivity between these apparently similar systems. TEMPO is an efficient catalyst in mild basic carbonate buffer, whereas NHPI acts efficiently in diluted acetic acid solution. Moreover, the effects of the alcohol type and the substituents were evaluated for a complete series of alcohols, and new kinetic data were obtained by means of voltammetric analyses and digital simulations of the cyclic voltammograms. Preparative electrocatalytic conversions of some alcohols were also examined under optimum conditions, and the results were encouraging. Voltammetry is applied as a versatile and informative technique to study the electrocatalytic performances of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) and N-hydroxyphthalimide (NHPI) towards alcohol oxidation in aqueous solutions. Voltammetric analyses confirm that both compounds act as powerful electrocatalysts for this type of reaction without the need of co-catalysts.