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Skeletal formula of 4-hydroxy-TEMPO
Ball-and-stick model of the 4-hydroxy-TEMPO molecule
IUPAC name
Other names
tempol; tanol; TMPN; 4-Oxypiperidol; nitroxyl 2; HyTEMPO
3D model (JSmol)
ECHA InfoCard 100.017.056
Molar mass 172.248 g·mol−1
Appearance Orange crystals
Melting point 71–73 °C (160–163 °F; 344–346 K)[1]
GHS pictograms GHS-pictogram-exclam.svg[2]
GHS signal word Warning[2]
H302, H315, H319, H335[2]
P261, P305+351+338[2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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, its major appeal over TEMPO is that is less expensive, 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.[3]

Example synthesis of 4-Hydroxy-TEMPO from phorone, which is itself make from acetone and ammonia

In biochemical research, 4-hydroxy-TEMPO has been investigated as an agent for limiting reactive oxygen species, it catalyzes the disproportionation of superoxide, facilitates hydrogen peroxide metabolism, and inhibits Fenton chemistry.[4]

4-Hydroxy-TEMPO is often present as a structural element in hindered amine light stabilizers, which are commonly used stabilizers in plastics. 4-Hydroxy-TEMPO, along with related nitroxides, are being studied for their potential antioxidant properties.[5]


  1. ^ Zakrzewski, Jerzy; Krawczyk, Maria (1 January 2011). "Reactions of Nitroxides. Part XII [1]. – 2,2,6,6-Tetramethyl-1-oxyl- 4-piperidyl Chloroformate – A New Reactive Nitroxyl Radical. A One-pot Synthesis of 2,2,6,6-Tetramethyl-1-oxyl-4-piperidyl N,N-Dialkyl-carbamates". Zeitschrift für Naturforschung B. 66 (5). doi:10.1515/znb-2011-0509.
  2. ^ a b c d Sigma-Aldrich Co., 4-Hydroxy-TEMPO. Retrieved on 2015-08-24.
  3. ^ Ciriminna, Rosaria; Pagliaro, Mario (15 January 2010). "Industrial Oxidations with Organocatalyst TEMPO and Its Derivatives". Organic Process Research & Development. 14 (1): 245–251. doi:10.1021/op900059x.
  4. ^ Wilcox, C. S.; Pearlman, A. (2008). "Chemistry and Antihypertensive Effects of Tempol and Other Nitroxides". Pharmacological Reviews. 60 (4): 418–69. doi:10.1124/pr.108.000240. PMC 2739999. PMID 19112152.
  5. ^ Lewandowski, M; Gwozdzinski, K. (2017). "Nitroxides as Antioxidants and Anticancer Drugs". International Journal of Molecular Sciences. 18 (11): 2490. doi:10.3390/ijms18112490.