# 4-Hydroxy-TEMPO

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> Source revision: 1309974924
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{{Short description|Heterocyclic compound bearing a stable aminoxyl radical}}
{{Chembox
|Watchedfields = changed
|verifiedrevid = 456502836
|ImageFile = 4-Hydroxy-TEMPO.svg
|ImageSize = 175
|ImageAlt = Skeletal formula of 4-hydroxy-TEMPO
|ImageFile1 = 4-Hydroxy-TEMPO radical ball.png
|ImageSize1 = 175
|ImageAlt1 = Ball-and-stick model of the 4-hydroxy-TEMPO molecule
|PIN = (4-Hydroxy-2,2,6,6-tetramethylpiperidin-1-yl)oxyl
|OtherNames = tempol; tanol; TMPN; 4-Oxypiperidol; nitroxyl 2; HyTEMPO
|Section1={{Chembox Identifiers
|CASNo_Ref = {{cascite|correct|CAS}}
|CASNo = 2226-96-2
|UNII_Ref = {{fdacite|correct|FDA}}
|UNII = U78ZX2F65X
|ChEMBL_Ref = {{ebicite|correct|EBI}}
|ChEMBL = 607023
|PubChem = 137994
|ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
|ChemSpiderID = 121639
|ChEBI = 180664
|SMILES = CC1(C)CC(O)CC(C)(C)N1[O]
|InChI = 1S/C9H18NO2/c1-8(2)5-7(11)6-9(3,4)10(8)12/h7,11H,5-6H2,1-4H3
|InChIKey = UZFMOKQJFYMBGY-UHFFFAOYSA-N
|StdInChI_Ref = {{stdinchicite|correct|chemspider}}
|StdInChI = 1S/C9H18NO2/c1-8(2)5-7(11)6-9(3,4)10(8)12/h7,11H,5-6H2,1-4H3
|StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
|StdInChIKey = UZFMOKQJFYMBGY-UHFFFAOYSA-N
}}
|Section2={{Chembox Properties
|C=9|H=18|N=1|O=2
|Appearance = Orange crystals
|MeltingPtC = 71–73
|MeltingPt_ref = <ref>{{cite journal|last1=Zakrzewski|first1=Jerzy|last2=Krawczyk|first2=Maria|title=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|journal=Zeitschrift für Naturforschung B|date=1 January 2011|volume=66|issue=5|pages=493–498 |doi=10.1515/znb-2011-0509|s2cid=51802316 |doi-access=free}}</ref>
|Solubility = 629.3 g/L (20 °C)}}
|Section3={{Chembox Hazards
|GHSPictograms = {{GHS07}}<ref name="sigma">{{Sigma-Aldrich|id=176141|name=4-Hydroxy-TEMPO|accessdate=2015-08-24}}</ref>
|GHSSignalWord = Warning<ref name="sigma" />
|HPhrases = {{H-phrases|302|315|319|335}}<ref name="sigma" />
|PPhrases = {{P-phrases|261|305+351+338}}<ref name="sigma" />
}}
}}

'''4-Hydroxy-TEMPO''' or '''TEMPOL''', formally 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, is a [heterocyclic compound](/source/heterocyclic_compound). Like the related [TEMPO](/source/TEMPO), it is used as a [catalyst](/source/catalyst) and chemical [oxidant](/source/oxidant) by virtue of being a stable [aminoxyl radical](/source/aminoxyl_radical). Its major appeal over TEMPO is that it is less expensive, being produced from [triacetone amine](/source/triacetone_amine), which is itself made via the condensation of [acetone](/source/acetone) and [ammonia](/source/ammonia). This makes it economically viable on an industrial scale.<ref>{{cite journal|last1=Ciriminna|first1=Rosaria|last2=Pagliaro|first2=Mario|title=Industrial Oxidations with Organocatalyst TEMPO and Its Derivatives|journal=Organic Process Research & Development|date=15 January 2010|volume=14|issue=1|pages=245–251|doi=10.1021/op900059x}}</ref>

[[File:4-Hydroxy-TEMPO synthesis01.svg|thumb|center|350px|Example synthesis of 4-Hydroxy-TEMPO from [phorone](/source/phorone), which is itself made from acetone and ammonia]]

In biochemical research, 4-hydroxy-TEMPO has been investigated as an agent for limiting [reactive oxygen species](/source/reactive_oxygen_species).  It catalyzes the [disproportionation](/source/disproportionation) of [superoxide](/source/superoxide), facilitates [hydrogen peroxide](/source/hydrogen_peroxide) metabolism, and inhibits [Fenton](/source/Fenton's_reagent) chemistry.<ref>{{cite journal | doi = 10.1124/pr.108.000240 | title = Chemistry and Antihypertensive Effects of Tempol and Other Nitroxides | year = 2008 | last1 = Wilcox | first1 = C. S. | last2 = Pearlman | first2 = A. | journal = Pharmacological Reviews | volume = 60 | issue = 4 | pages = 418–69 | pmid = 19112152 | pmc = 2739999}}</ref> 4-Hydroxy-TEMPO, along with related [nitroxide](/source/nitroxide)s, are being studied for their potential antioxidant properties.<ref>{{cite journal | doi = 10.3390/ijms18112490 | title = Nitroxides as Antioxidants and Anticancer Drugs | year = 2017 | last1 = Lewandowski | first1 = M | last2 = Gwozdzinski  | first2 = K. | journal = International Journal of Molecular Sciences | volume = 18 | issue = 11 | pages = 2490 | pmid = 29165366 | pmc = 5713456| doi-access = free }}</ref>

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

It is a promising model substance to inhibit SARS-CoV-2 RNA-dependent RNA polymerase.<ref>{{cite journal | doi = 10.1126/science.abi5224 | title = Fe-S cofactors in the SARS-CoV-2 RNA-dependent RNA polymerase are potential antiviral targets | year = 2021 | last1 = Maio| first1 = N. | last2 = Lafont| first2 = B.A.P. | last3 = Sil| first3 = D. | last4 = Li| first4 = Y. | last5 = Bollinger | first5 = M. | last6 = Krebs | first6 = C. | journal = Science | volume = 373 | issue = 6551 | pages = 236–241 | pmid = 34083449 | pmc = 8892629 | bibcode = 2021Sci...373..236M | doi-access = free }}</ref>

==See also==
* [Bobbitt's salt](/source/Bobbitt's_salt)
* [pH neutral aqueous organic flow batteries](/source/Flow_battery)

==References==
{{Reflist}}

{{DEFAULTSORT:Hydroxy-TEMPO, 4-}}
Category:Free radicals
Category:Amine oxides
Category:Piperidines

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Adapted from the Wikipedia article [4-Hydroxy-TEMPO](https://en.wikipedia.org/wiki/4-Hydroxy-TEMPO) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/4-Hydroxy-TEMPO?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.