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 aminoxyl radical. Its major appeal over TEMPO is that it 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 made from acetone and ammonia

4-Hydroxy-TEMPO

Names
Preferred IUPAC name (4-Hydroxy-2,2,6,6-tetramethylpiperidin-1-yl)oxyl
Other names tempol; tanol; TMPN; 4-Oxypiperidol; nitroxyl 2; HyTEMPO
Identifiers
CAS Number	2226-96-2 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:180664
ChEMBL	ChEMBL607023 Y
ChemSpider	121639 Y
ECHA InfoCard	100.017.056
PubChem CID	137994
UNII	U78ZX2F65X Y
CompTox Dashboard (EPA)	DTXSID4041280
InChI InChI=1S/C9H18NO2/c1-8(2)5-7(11)6-9(3,4)10(8)12/h7,11H,5-6H2,1-4H3 Y Key: UZFMOKQJFYMBGY-UHFFFAOYSA-N Y InChI=1S/C9H18NO2/c1-8(2)5-7(11)6-9(3,4)10(8)12/h7,11H,5-6H2,1-4H3 Key: UZFMOKQJFYMBGY-UHFFFAOYSA-N
SMILES CC1(C)CC(O)CC(C)(C)N1[O]
Properties
Chemical formula	C9H18NO2
Molar mass	172.248 g·mol−1
Appearance	Orange crystals
Melting point	71–73 °C (160–163 °F; 344–346 K)[1]
Solubility in water	629.3 g/L (20 °C)
Hazards
GHS labelling:
Pictograms	[2]
Signal word	Warning[2]
Hazard statements	H302, H315, H319, H335[2]
Precautionary statements	P261, P305+P351+P338[2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

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, along with related nitroxides, are being studied for their potential antioxidant properties.^[5]

On an industrial-scale 4-hydroxy-TEMPO is often present as a structural element in hindered amine light stabilizers, which are commonly used stabilizers in plastics, it is also used as a polymerisation inhibitor, particularly during the purification of styrene.

It is a promising model substance to inhibit SARS-CoV-2 RNA-dependent RNA polymerase.^[6]

See also

• pH neutral aqueous organic flow batteries

References

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): 493–498. doi:10.1515/znb-2011-0509. S2CID 51802316.
2. 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. PMC 5713456. PMID 29165366.
6. Maio, N.; Lafont, B.A.P.; Sil, D.; Li, Y.; Bollinger, M.; Krebs, C. (2021). "Fe-S cofactors in the SARS-CoV-2 RNA-dependent RNA polymerase are potential antiviral targets". Science. 373 (6551): 236–241. doi:10.1126/science.abi5224. PMC 8892629. PMID 34083449.