4-Hydroxy-TEMPO

4-Hydroxy-TEMPO or TEMPOL, formally 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, is a heterocyclic compound. Like the related TEMPO, it is used as a catalyst and chemical oxidant by virtue of being a stable radical. It's major appeal over TEMPO is that is significantly cheaper, being produced from triacetone amine, which is itself made via the condensation of acetone and ammonia. This makes it economically viable on an industrial scale.