TEMPOmediated

TEMPO-mediated oxidation refers to catalytic oxidation reactions in which the nitroxyl radical TEMPO acts as a redox mediator to convert alcohols into aldehydes or ketones. In these systems TEMPO cycles between its radical form and the oxoammonium ion TEMPO+, enabling hydrogen abstraction and carbonyl formation under relatively mild conditions.

The catalytic cycle typically involves oxidation of TEMPO to TEMPO+ by a co-oxidant, such as aqueous sodium hypochlorite (bleach), Oxone, or other oxidants. TEMPO+ then abstracts a hydrogen from an alcohol, forming the carbonyl product and a reduced TEMPO species. This reduced form is reoxidized by the same co-oxidant to regenerate TEMPO+, closing the cycle. The choice of co-oxidant, solvent, pH, and temperature determines whether primary alcohols are selectively oxidized to aldehydes or allowed to progress to carboxylic acids, and whether secondary alcohols are converted to ketones.

Variants of TEMPO-mediated oxidation include copper-catalyzed or copper-free systems that enable aerobic oxidation with molecular oxygen or air as the terminal oxidant. Such Cu/TEMPO protocols can operate under milder, more eco-friendly conditions and are useful for late-stage oxidation in complex molecules. Other approaches employ catalytic TEMPO with periodic oxidants or enzymatic co-factors to expand scope.

Applications of TEMPO-mediated oxidation span organic synthesis, medicinal chemistry, and carbohydrate chemistry, where chemoselective and mild oxidation of alcohols is advantageous. Limitations include dependence on the oxidant system, potential over-oxidation, and the cost or scalability of TEMPO catalysts in some processes.